Engine Hunts at Start and Then Rough Idle When Warm

[lazabby]

My problems started a few weeks ago. The engine was running very well except for a minor hot start issue. I had the injectors cleaned. Now the
engine hunts when first starting for about a minute. I assume it does this while the cold start injectors is active. Here is a video of it hunting and then suddenly stopping:
https://youtu.be/4FEjgP0si2U

The idle once warmed up is rough. I've been trying to put a dwell meter and check the idle but no matter which way I adjust the screw the dwell reading does not change. Could the CO plug be bad? Here is a video after the engine has warmed up.

https://youtu.be/6QxHJeUyQsE

What do I need to fix?

[Bitsyncmaster]

Cold start injector only fires when the starter is turning.

You probably need a mixture adjustment after your injectors were cleaned. But if you don't get any dwell reading you may have a component failure. Is your FV buzzing?

[Elvis]

Hi Shannon - what dwell are you reading ? from the ignition ???



Didn't you install an EFI some years ago when you asked people how the idle works ?

[lazabby]

Cold start injector only fires when the starter is turning.

You probably need a mixture adjustment after your injectors were cleaned. But if you don't get any dwell reading you may have a component failure. Is your FV buzzing?

It seems to be buzzing as it feels like it when I place my hand on it.

[lazabby]

Hi Shannon - what dwell are you reading ? from the ignition ???



Didn't you install an EFI some years ago when you asked people how the idle works ?

I don't have the EFI anymore. I have the stock engine now. The dwell meter is hooked to the diagnostic plug by the firewall. You can see it in the video.

[Bitsyncmaster]

I don't have the EFI anymore. I have the stock engine now. The dwell meter is hooked to the diagnostic plug by the firewall. You can see it in the video.

If the FV is buzzing you should be reading some dwell. There is a two pin connector with an orange wire and purple wire on your engine harness. The orange wire is what connects to the diagnostic port. You can also read dwell right off the FV wire.

[Elvis]

My diagnostic plug is further down ond the left and black and not visible on the video !?!?!?!


BTW - I only use an oscilloscope for these adjustments, just in case you know someone...


Didn't you say that EFI is much easier, more fuel efficient and gets you more power ?
What was the reason to go back to stock ?

[David T]

My diagnostic plug is further down ond the left and black and not visible on the video !?!?!?!


BTW - I only use an oscilloscope for these adjustments, just in case you know someone...


Didn't you say that EFI is much easier, more fuel efficient and gets you more power ?
What was the reason to go back to stock ?


If you get a dwell reading, any reading, and it doesn't change, it means you are in "open loop" where the ECU is outputting a fixed dwell. You need to get the ECU into "Closed Loop", that is where it responds to changes from the O2 sensor and adjusts the frequency valve accordingly. If you are stuck in open loop the motor hasn't warmed up, or a senor is bad or disconnected.

[Farrar]

I would check the oxygen sensor for proper function.

[NckT]

Disconnect the oxygen sensor electrical connection at the rear firewall on the drivers side under the wooden board (follow the 4mm ish thick blue cable from the fuel computer). Once done, the frequency valve should then buzz and the dwell should be 45deg / 50%

If it is then the oxygen sensor is not working or you simply haven't adjustex the mixture far enough and the dwell is at saturation resulting in the frequency valve not buzzing (most likely)

If it isn't then there's a problem with the operation of the fuel computer so check fuse no.7 and the lambda relay for correct type

Good luck

[David T]

If he is getting dwell readings the Lambda ECU is getting power and it is working, it just isn't in closed loop. There are tests you can do (grounding the O2 lead or putting 1.5 DC volts on it) to make sure the Lambda ECU is working. Once you prove out the ECU then the O2 sensor is probably bad or the mixture screw is WAY out of adjustment. Refer to D:04:15 for the specific tests. Also read the system notes on the previous page.

[lazabby]

This has me puzzled. I replaced the fuel injectors and the engine is running better. When I start the engine, it hunts fr about three minutes and then it settles down and idles fairly decently. Occasionally it will suddenly start hunting again briefly and settle down. After it warmed up and the fans came on and off several times, I put a dwell meter on it to check it. It consistently stays between 10-11. The other day it seemed to be fluctuating in the 30-50 range so I don't know what has happened.
https://youtu.be/8Ca4UV654cE

What's going on? Bad O2 sensor?

[Bitsyncmaster]

Did you readjust the mixture when you installed the new injectors?

[lazabby]

Did you readjust the mixture when you installed the new injectors?

Yes, I've tried to but I've had to do it by ear since I can't seem to get the reading off the meter.

I actually drove the car yesterday down to the street and back. It actually drove well. But I know that the tune is not dialed in. I plan to start the car this morning o see if it still hunts when cold but my bet is that it still does.

[Bitsyncmaster]

Yes, I've tried to but I've had to do it by ear since I can't seem to get the reading off the meter.

I actually drove the car yesterday down to the street and back. It actually drove well. But I know that the tune is not dialed in. I plan to start the car this morning o see if it still hunts when cold but my bet is that it still does.

If you make adjustments to the mixture for best idle (by ear) it will cause other more important problems.

[lazabby]

If you make adjustments to the mixture for best idle (by ear) it will cause other more important problems.

Yes, I've adjusted it so that it doesn't hunt when warm. Did yo use my video? I'm trying to figure out why the meter reading is between and not in the 30-50 range.

[opethmike]

Yes, I've adjusted it so that it doesn't hunt when warm. Did yo use my video? I'm trying to figure out why the meter reading is between and not in the 30-50 range.

Is it set to 4 cylinder mode?

[Jonathan]

This has me puzzled. I replaced the fuel injectors and the engine is running better. When I start the engine, it hunts fr about three minutes and then it settles down and idles fairly decently. Occasionally it will suddenly start hunting again briefly and settle down. After it warmed up and the fans came on and off several times, I put a dwell meter on it to check it. It consistently stays between 10-11. The other day it seemed to be fluctuating in the 30-50 range so I don't know what has happened.
https://youtu.be/8Ca4UV654cE

What's going on? Bad O2 sensor?

Hey Shannon, when I was doing some dwell meter/mixture setting troubleshooting and fine tuning, it did the same thing where it stayed at one reading instead of fluctuating and also tended to settle in after running for a few minutes. In my case, it turned out to be a bad O2 sensor.

I didn't manage to get my own O2 sensor out and replaced, so I took it to a shop I've used in the past and he got it out, replaced it and then set the dwell properly. Idle and fuel mileage has been good ever since.

I'm sure there is a more technical or scientific explanation as to what happens with that circuit when the O2 sensor fails to cause it to stay steady or not fluctuate or whatever. I don't have that explanation, but also figured I didn't need it after a new O2 sensor in my car fixed it all up anyway.

I couldn't get your youtube video to play by the way. It was marked as private.

[Bitsyncmaster]

If the mixture is to far off, the dwell will read solid low about 10 deg. or high about 85 deg.

[Chris 16409]

When my oxygen sensor went bad I had a pronounced hunting. Oscillation of the dwell meter needle is normal. Remember the lambda computer tries to maintain the correct dwell. If the mixture is set mecanically too lean, the computer attempts to richen the mixture and vice versa. If the mechanical adjustment is too far out of whack, the computer defaults to like a 40 to 50 percent duty cycle.

[lazabby]

Is it set to 4 cylinder mode?

Yes.

https://youtu.be/8Ca4UV654cE

[lazabby]

Hey Shannon, when I was doing some dwell meter/mixture setting troubleshooting and fine tuning, it did the same thing where it stayed at one reading instead of fluctuating and also tended to settle in after running for a few minutes. In my case, it turned out to be a bad O2 sensor.

I didn't manage to get my own O2 sensor out and replaced, so I took it to a shop I've used in the past and he got it out, replaced it and then set the dwell properly. Idle and fuel mileage has been good ever since.

I'm sure there is a more technical or scientific explanation as to what happens with that circuit when the O2 sensor fails to cause it to stay steady or not fluctuate or whatever. I don't have that explanation, but also figured I didn't need it after a new O2 sensor in my car fixed it all up anyway.

I couldn't get your youtube video to play by the way. It was marked as private.

Jonathan thanks. That's what I'm suspecting. I'll probably replace it.

Thanks for letting me know the setting on the video. Didn't know it was marked private.

[Jonathan]

You can also double check the O2 sensor reference ground wire is still connected properly. It is the one which grounds to the block under the air filter housing, pretty much in the far corner passenger side and towards the front of the car. You can identify it fairly easily because a couple inches of the ground wire has a red wrap on it. The wire is only six inches or so long and the free end has a black quick connector (very similar to the ones used on the ballast resistor connections). The other end of that wire ultimately connects with the ECU behind the driver's seat. It could be another wiring connection that's not making good contact or not connected at all perhaps. And easy enough to check.

52472

My photo is slightly misleading as I had to relocate mine since the hole it's meant to go into had a broken off screw in it. The red arrow points to the hole your red ground wire is probably screwed into.

[lazabby]

You can also double check the O2 sensor reference ground wire is still connected properly. It is the one which grounds to the block under the air filter housing, pretty much in the far corner passenger side and towards the front of the car. You can identify it fairly easily because a couple inches of the ground wire has a red wrap on it. The wire is only six inches or so long and the free end has a black quick connector (very similar to the ones used on the ballast resistor connections). The other end of that wire ultimately connects with the ECU behind the driver's seat. It could be another wiring connection that's not making good contact or not connected at all perhaps. And easy enough to check.

52472

My photo is slightly misleading as I had to relocate mine since the hole it's meant to go into had a broken off screw in it. The red arrow points to the hole your red ground wire is probably screwed into.

The ground is there. I replaced the O2 sensor but I'm still getting a reading between 10.5 and 11 on the dwell meter at 4 cylinder. You can see it on the video. What's going on? The car still hunts a little when starting but smooths out when warm.

[opethmike]

The ground is there. I replaced the O2 sensor but I'm still getting a reading between 10.5 and 11 on the dwell meter at 4 cylinder. You can see it on the video. What's going on? The car still hunts a little when starting but smooths out when warm.

What do you get with the sensor unplugged?

[Jonathan]

What do you get with the sensor unplugged?

Mike's thinking the same thing I was... to confirm what you get for each of the troubleshooting steps:

52526

[lazabby]

Mike's thinking the same thing I was... to confirm what you get for each of the troubleshooting steps:

52526

I'll try it with the sensor unplugged. Might take a day or two to get back with a response.

[Bitsyncmaster]

What do you get with the sensor unplugged?

That number is saying your mixture is pretty far off. The ECU has maxed out it's adjustment range. Move your mixture screw a little bit one way or the other and see if that number changes.

[opethmike]

That number is saying your mixture is pretty far off. The ECU has maxed out it's adjustment range. Move your mixture screw a little bit one way or the other and see if that number changes.

I am thinking the same thing.

Shannon, any chance you can get a hold of a wideband O2? That could aid quite a bit.

[Morpheus]

Lean it out a bit and see if it changes.

[Jonathan]

Lean it out a bit and see if it changes.

And for the sake of clarity, the lean direction for that adjustment screw is clockwise or counterclockwise?

Also, "a little bit" is not very much. I recall when I was looking over my mechanic's shoulder while we were adjusting things, the full range from a lean stall to a rich stall was a half turn. Meaning, if you put your screw driver in that hole and it is lining up with say the 12 o'clock on a clock face, you are only going to want to go a few MINUTES of equivalent turn as the entire span would only be about from the 9 o'clock position to the 3 o'clock position. Less is more with these adjustments. Make a tiny change, then give it a chance to make an impact. Then make another small change. And don't forget where your starting reference point was.

[Morpheus]

And for the sake of clarity, the lean direction for that adjustment screw is clockwise or counterclockwise?


CCW = lean, CW = enrich

"A little bit" is a relative turn, but I would say if you are using a long "T" handle allen wrench, you would equate it to a 1/16th of a turn or less. A minuscule adjustment makes a big difference when dialing in the CO.

[Bitsyncmaster]

And for the sake of clarity, the lean direction for that adjustment screw is clockwise or counterclockwise?

Also, "a little bit" is not very much. I recall when I was looking over my mechanic's shoulder while we were adjusting things, the full range from a lean stall to a rich stall was a half turn. Meaning, if you put your screw driver in that hole and it is lining up with say the 12 o'clock on a clock face, you are only going to want to go a few MINUTES of equivalent turn as the entire span would only be about from the 9 o'clock position to the 3 o'clock position. Less is more with these adjustments. Make a tiny change, then give it a chance to make an impact. Then make another small change. And don't forget where your starting reference point was.

It's more like a 1/4 turn to go from one extreme dwell reading (10 deg) to the other (85 deg.). I have not test it to engine stall.

[lazabby]

Here is an update and mostly the news is good. Per the suggestion in the thread, I unplugged my CO2 sensor. The car was running and up to operating temperature with fans cycling. I plugged in the dwell meter. As before, the reading was between 10.5 and 11. I then unplugged the CO2 sensor and the dwell meter reading went up to about 44.7 with little variation. Here is the video of that:
https://youtu.be/clMgiVDDjhQ
Whatever adjustment I did on the idle mixture screw did not budge the reading.

I then plugged the CO2 sensor back in and the dwell meter began fluctuating as it should. I then worked on the tune and here is what I believe is the last video I took:
https://youtu.be/CMB0WZUy0ao

The engine actually ran a little bit smoother a couple of days ago when I was unable to get a good reading. If you listen carefully to the video the engine isn't quite smooth but it runs well enough now to drive around. This morning I started the car with a cold engine and it fired up almost immediately. The idle wasn't fluctuating but I would like to smooth it out a little more. I'm not sure if I need to barely tweak the mixture screw or if it's something else.

Bottom line is that I have a driveable car. I''l probably get a few miles on it and put the meter on it again and make a very slight adjustment.

Any other tips?

[Bitsyncmaster]

You will get a smoother idle running the mixture rich. But then you get bad MPG, smelly exhaust, damaged CAT. Is that smooth idle really that important?

[lazabby]

I took it out for a longer drive yesterday. It hunted a bit when first started. I turned on the AC after a few minutes after it was warm and noticed that the RPM was surging erratically. What's going on? Turned off, the idle was fairly stable.

[lazabby]

I'm still having an issue where my car hunts when cold. I can drive the car around and get it warm and put a dwell meter on it but the dwell meter is not getting a good reading whether in the "unused" plug or at the bulkhead. Instead of fluctuating it hangs about 54.8 (at 4 cylinders). I can't understand why it's doing that. the CO2 is new. The car runs fine when warm. I really want to get rid of the hunting when cold.

[Elvis]

Read the manual, there is no closed loop control when cold.


repetition: PID controller can't handle dead times. cold engine - richt mixture - slow reaction - dead time !


10 years ago I suggested to modify the idle ECU to improve the reaction time, but I was called stupid
for doing that...delorean has to hunt...

[Bitsyncmaster]

I'm still having an issue where my car hunts when cold. I can drive the car around and get it warm and put a dwell meter on it but the dwell meter is not getting a good reading whether in the "unused" plug or at the bulkhead. Instead of fluctuating it hangs about 54.8 (at 4 cylinders). I can't understand why it's doing that. the CO2 is new. The car runs fine when warm. I really want to get rid of the hunting when cold.

Your wide open throttle switch is stuck on or less likely your "idle speed regulator switch" is shorted. Just pull one wire off the wide open throttle switch.

[David T]

There is no getting around the PRV hunting when cold. You can reduce it but not eliminate it. To reduce it to a minimum you must get each cylinder set up as close to each other as possible in terms of adjustments. That means checking (and if necessary adjusting) the valve clearances, spark plug etc. The cylinder pressures must be within 5% of each other too. Even in closed loop it will "hunt" a little as the frequency valve modulates.

[MikeWard]

There is no getting around the PRV hunting when cold.
With respect David, that is total bollocks

[David T]

With respect David, that is total bollocks

I am guessing here but I think "total bollocks" loosely translates to "total bullsh-t" in American English. Must be a British saying I assume. Anyway addressing your point, if you disable the idle motor and the Lambda system you can get the PRV to run pretty smoothly, even cold. My point in saying the PRV hunts is that with all of the stock engine systems in place and operating as intended, hunting is normal. The more you open the air screws and bypass the idle motor, the smoother it may run but the idle motor will have less and less control. It needs that control so that when you are running the A/C it can keep the motor from slowing down as the compressor clutch engages. It also helps to prevent stalling as you release the clutch going into first from a stop. Hunting is to be considered "normal" even by the specifications. If you refer to the Workshop Manual, in several places you will find the idle spec to be plus or minus 50 RPM's in recognition of the fact that the motor will hunt normally. It is not that the speed is supposed to be 775 plus-minus, it is that the speed will vary above and below 775 RPM's and still be within spec. I refer you to D:05:02 System Notes #5.

[Bitsyncmaster]

The stock idle ECU has no fancy crystal controlled clock and fancy digital logic. The idle speed tolerance would be the tolerance of the idle ECU components and the variable of aging and heat changing those component values.

[Elvis]

... It is not that the speed is supposed to be 775 plus-minus, it is that the speed will vary above and below 775 RPM's and still be within spec. I refer you to D:05:02 System Notes #5.

That's just your interpretation David.




Funny that nobody seems to understand what a PID controller does with a dead time.

I learned this an a college in California...any my friend Jordan recognized the dead-time / slow
reaction...

[NckT]

That's just your interpretation David.




Funny that nobody seems to understand what a PID controller does with a dead time.

I learned this an a college in California...any my friend Jordan recognized the dead-time / slow
reaction...

I understand PID control. I tried to explain the control function of the engine control in post no.19 in:

http://dmctalk.org/showthread.php?15633-Attempting-to-destroy-my-idle-lumpiness/page2

[lazabby]

It appears I cannot get to closed loop. I unplugged the WOT and I'm still getting a dwell reading of about 53.8 on the dwell meter (4 cylinder). The RPM ran about 1200 but once I plugged the WOT back in the RPM settled back down to about 800. I unplugged the CO2 and got the same reading. Plugged it back in and got the same reading. The CO2 is new. Perhaps the wire on the CO2 is bad?

[NckT]

It appears I cannot get to closed loop. I unplugged the WOT and I'm still getting a dwell reading of about 53.8 on the dwell meter (4 cylinder). The RPM ran about 1200 but once I plugged the WOT back in the RPM settled back down to about 800. I unplugged the CO2 and got the same reading. Plugged it back in and got the same reading. The CO2 is new. Perhaps the wire on the CO2 is bad?

You'll get the figure of approx 54 deg if the switch on the wide open throttle is closed OR the lambda temp switch is closed.

When the coolant temp is above 80 c, the lambda switch will then open (with the wide open switch is open), before the ecu will operate in closed loop mode using the oxygen sensor voltage input as reference, or it will default to 45 deg. The design is that the fuel computer will only operate in closed loop mode once the engine is at this temperature.

You could remove the fuel computer electrical plug and remove pin 7 that will remove the lambda and wot switch inputs to the ecu and then see if you get a varying dwell with a hot engine. OR on a hot engine, disconnect the wot and check to see if you get continuity between pin 7 and pin 5. This will determine if the lambda switch is open or closed. It should be open circuit on a hot engine.

I hope I've explained this ok so far.

Good luck Shannon

[Bitsyncmaster]

I agree you should get the wire disconnected to trouble shoot if it's the temp switch or the lambda ECU bad. Most owners probably won't attempt to remove a pin from the lambda ECU connector (although it's not hard to do with experience). You could also disconnect the wire at the bulkhead connector but those female pins are hard to pull from the connector. Another option is to cut the wire and then join it back when your testing is done.

Since your holding that 54 degree dwell it must be the temp switch or lambda ECU bad.

[Elvis]

You'll get the figure of approx 54 deg if the switch on the wide open throttle is closed OR the lambda temp switch is closed.

When the coolant temp is above 80 c, the lambda switch will then open (with the wide open switch is open), before the ecu will operate in closed loop mode using the oxygen sensor voltage input as reference, or it will default to 45 deg. The design is that the fuel computer will only operate in closed loop mode once the engine is at this temperature.

...

Nick, please explain - 80°C ?

the manual says 15°C ?!? D:04:10

before 80°C the ecu operates in closed loop mode ?

Sorry I'm confused. What am I gettting wrong ?


@ Shannon - for the O2 sensor to operate it needs 300°C. It then will generate a "high" voltage (1V ?!?) that
will activate the ECU into closed loop mode. Before that - it will stay at the cold / enrich PWM.
This can take a while and sitting in the garage at idle in cold weather - will take a long time.
I've seen that some weeks ago when I measured my lambda ECU and O2 sensor. I was close to replace the
sensor but before that I talked to a friend who is a car genious and runs his own shop. He told me to wait
or drive the car to heat the sensor up above 300°C.

[NckT]

I made a mistake, it is 15 c not 80 c as I said. (That's the last time I try and convert c to Fahrenheit in my head as I got that completely wrong too as it's 59 not 80 ! :)

The o2 sensor will give a sinusoidal voltage signal between 0.2 to 0.8 volts.

[lazabby]

I agree you should get the wire disconnected to trouble shoot if it's the temp switch or the lambda ECU bad. Most owners probably won't attempt to remove a pin from the lambda ECU connector (although it's not hard to do with experience). You could also disconnect the wire at the bulkhead connector but those female pins are hard to pull from the connector. Another option is to cut the wire and then join it back when your testing is done.

Since your holding that 54 degree dwell it must be the temp switch or lambda ECU bad.

I'm working on getting back to this issue. I still have some hunting when I start that smooths out in about a minute or two. I'm still getting a dwell reading of around 54 with little fluctuation. I'm about to borrow someone else's lambda ECU to see it the reading changes.

Is the wire from the CO2 to the lambda ECU suppose to show a voltage? I put a multimeter on the wire where it connects to the wire going directly to the ECU. I didn't read any voltage. I will say that I may not have set the multimeter to the right setting (200ma) or perhaps it was not grounded properly. I also found a small cut in the wire. It looks like a few strands may have been cut. The CO2 sensor is fairly new, replaced last year.

[NckT]

If the lambda switch is closed, the ecu will always default the frequency valve to dwell of 54, regardless of what the O2 sensor signal is, so replacing the ecu with another one is very likely to give you the same result. So try the following test:

.....on a hot engine, disconnect the wot and check to see if you get continuity between pin 7 and pin 5. This will determine if the lambda switch is open or closed. It should be open circuit on a hot engine........

[lazabby]

If the lambda switch is closed, the ecu will always default the frequency valve to dwell of 54, regardless of what the O2 sensor signal is, so replacing the ecu with another one is very likely to give you the same result. So try the following test:

.....on a hot engine, disconnect the wot and check to see if you get continuity between pin 7 and pin 5. This will determine if the lambda switch is open or closed. It should be open circuit on a hot engine........

I was looking at the wide open throttle (WOT) microswitch. It has two "plungers" in it. I believe the top one if for the automatic transmission kickdown (my car is auto). The lower one is for the lambda. The lower plunger is pushed in and will not move while the upper one freely moves when depressed. Can the lower one be the problem and is there a way to lubricate it or fix it so that it freely moves?

[NckT]

I was looking at the wide open throttle (WOT) microswitch. It has two "plungers" in it. I believe the top one if for the automatic transmission kickdown (my car is auto). The lower one is for the lambda. The lower plunger is pushed in and will not move while the upper one freely moves when depressed. Can the lower one be the problem and is there a way to lubricate it or fix it so that it freely moves?

Possibly. Try the following test:

.....on a hot engine, disconnect the wot and check to see if you get continuity between pin 7 and pin 5. This will determine if the lambda switch is open or closed. It should be open circuit on a hot engine.....

If you disconnect the wot switch and the dwell operates as normal, you've narrowed it down to the stuck-on wot microswitch. Electrical switch cleaner should help unstick it and clean the contacts.

Trust me ;)

Good luck

[David T]

If a micro switch is stuck it will stick again. They are not expensive so just replace it. In the meantime just disconnect it and see if you can get into "closed loop" ie, the dwell fluctuates.

[lazabby]

If a micro switch is stuck it will stick again. They are not expensive so just replace it. In the meantime just disconnect it and see if you can get into "closed loop" ie, the dwell fluctuates.

I unplugged the microswitch, took the car for a drive to get it warm. When I got back I put a dwell meter on it and it fluctuated normally. It was within normal range so now I know the microswitch needs to be replaced. I still have the hunting when I first start that disappears suddenly in about a minute. Could this be the lambda ECU? I borrowed one to switch out if I need to test this.

[Jonathan]

Shannon, more info, photos and links for those microswitches here: http://dmctalk.org/showthread.php?13810-Idle-Switch-Wiring

[David T]

It is normal for the motor to hunt for a moment when first started and cold.

[lazabby]

If the lambda switch is closed, the ecu will always default the frequency valve to dwell of 54, regardless of what the O2 sensor signal is, so replacing the ecu with another one is very likely to give you the same result. So try the following test:

.....on a hot engine, disconnect the wot and check to see if you get continuity between pin 7 and pin 5. This will determine if the lambda switch is open or closed. It should be open circuit on a hot engine........

Nick, You were right. It turned out to be the wide open throttle switch. I unplugged it and go the normal swing on the dwell meter. Turned out it was within normal range. I need to replace the WOT.

I started the car this morning and it still hunts when cold. Need ideas of what to look for.

[lazabby]

It is normal for the motor to hunt for a moment when first started and cold.

A few monts ago before I had to replace my injectors the engine did not hunt when cold. The car started right up and had a steady idle.

[NckT]

What reading do you get on the dwell on a warm engine now?

[NckT]

You could look into what I put in post No.23 (#23) in:

http://dmctalk.org/showthread.php?15633-Attempting-to-destroy-my-idle-lumpiness/page3

Good luck

[lazabby]

What reading do you get on the dwell on a warm engine now?


THe dwell is between 35-45.

[David T]

When the motor first starts, cold, it starts on the cold start valve. It is not exactly metered and is overly rich. Kind of like a choke on a carbureated car. It only squirts while cranking so it stops shooting in fuel quickly but it takes a moment for all of that fuel to be vaporized and consumed. Once consumed the motor has to "get used to" the leaner mixture so it slows down, overshoots, the idle motor overcompensates, the idle shoots up and the idle motor has to again compensate. The pulses dampen out but it takes a few cycles. The idle ECU does not communicate with the Ignition ECU or the Lambda ECU so they all act simultaneously sometimes against each other. Each ECU operates independently but are connected because they all control the same motor but each has it's own function so some functions overlap and some don't. The quality of the idle is very dependent on all of the cylinders working exactly equally. Especially till the motor warms up and the Lambda ECU can get into "Closed Loop".
Bottom line, some hunting when cold is to be considered normal and you do not try to "fix" it.

[NckT]

You could look into what I put in post No.23 (#23) in:

http://dmctalk.org/showthread.php?15633-Attempting-to-destroy-my-idle-lumpiness/page3

Good luck

Video evidence of non hunting when cold is in post No.30

http://dmctalk.org/showthread.php?15633-Attempting-to-destroy-my-idle-lumpiness/page3

[lazabby]

Video evidence of non hunting when cold is in post No.30

http://dmctalk.org/showthread.php?15633-Attempting-to-destroy-my-idle-lumpiness/page3

Are you absolutely sure you're not making a trip to Houston Texas any time soon? We have nice hot weather, great BBQ, great beer and NASA is not too far away plus Delorean Motor company is in the area. I'm sure we can round up a few cars for you to tinker with. :)

[NckT]

I would love to come over to visit, when I get some time/ funds. I'm definitely sold on Beer and BBQ ;)

[lazabby]

I have dwell meter and multimeter. What setting does one use to check the RPM of the engine and where are the probes placed in the engine?

[Bitsyncmaster]

Most RPM meters use the ignition coil (negative side). There are some optical RPM meters but you usually need to add a foil reflector on the pulley.