idle air control test procedure

[m_w]

I'm trying to diagnose an idle problem and am suspecting the iac valve could be bad. I can't find a testing procedure in the manual, and I can't find the procedures on the forums either. I thought dave from dmcmw posted a fairly detailed test at one point, but I can't find it. Can anyone help me out?

[sdg3205]

With the car running, unplug the outer idle ecu plug. RPM should spike to 2200 to 2500 if ISM and ecu are doing their job

[DMCVegas]

I ended up with a bad wire on mine for some reason. A solid check would be to check the resistance across all three wires, and ensure that there is none.

[m_w]

sdg3250 got most of the answer I was looking for. I eventually found the thread I was thinking of: http://dmctalk.org/showthread.php?9680-How-much-air-does-the-idle-speed-motor-move&highlight=idle+regulator

Two fast idle motor tests.

1 - Open up the driver side electrical compartment and locate the idle ECU (the black one on top). Start the engine. Pull out the plug closest to the center of the car. The idle should take off to about 2200RPM. Plug it back in and it should settle down. If this works, the ECU and the idle motor are good.

2 - Remove the hose between the idle motor and the cold start injector. Look down the throat of the idle valve. Have an assistant turn the key to the run position but do not start the car. The valve should immediately open up all the way, and then over about a 30-second period gradually close all the way. This shows that the valve is good, not sticky, and the electronics are working.

I also see I was in Chevy world when I named this thread. I meant Idle Speed Regulator, not Idle Air Control Valve.

Thanks for the help!

[Rich]

I'm trying to diagnose an idle problem and am suspecting the iac valve could be bad. I can't find a testing procedure in the manual, and I can't find the procedures on the forums either.

For testing see info. below in italics. It's taken from K-Jet.org. It first tells you how to check the motor condition via a resistance check on the IAC connector pins. It then goes on to explain how to go after the mechanical end of it.

Dave did mention something about the connectors themselves sometime going bad as I recall. Check the wiring close to the IAC motor to be sure it's OK.



Another way to test the idle air motor is to measure the resistance with your multimeter. A good motor should read +/-20 ohms resistance between any two pins that are next to eachother and +/-40 ohms resistance between the two outside pins.

The idle air motor can be cleaned out if it is not too damaged. The most common way to do this is to detach the motor from the car and spray it out with carb cleaner. Fill the motor with carb cleaner and plug both openings in it. Shake it up and roll it back and forth in between your hands like you are making a ‘snake’ out of clay. You should hear it clicking back and forth. Repeat the cleaning process several times, drain the motor, and then allow it to dry for an hour or so.

source page: LINK: http://www.k-jet.org/articles/information/k-jet-debugging-guide/#41 (http://www.k-jet.org/articles/information/k-jet-debugging-guide/#41)

[m_w]

The Wiring is new (NOS 1983 harnesses in the engine bay). I did the second test in my previous post, these were my results.
- 1st attempt - valve opened slowly and part of the way. Then closed slowly.
- 2nd attempt - valve opened quickly, did not close at all.

Through both attempts (and previously) the regulator was humming loudly and vibrating.

I might try to clean it, but more likely (because of the noise it was making), I'll just order a new one.

Thanks

[Farrar]

Not sure if this is 100% applicable, but I got this from a generic CIS tech book:


Start the engine and make sure the valve is vibrating and humming slightly. If not, check for a voltage signal reaching the valve and check the valve's resistance. With ignition on, the voltage at the harness connector should be approximately 12 volts (battery voltage) between the center terminal and ground, and 10 volts between the center terminal and the outer two terminals. Check the resistance on the connector terminals of the idle air stabilizer valve. There should be continuity between the center terminal and each of the outer terminals. If the readings are incorrect, replace the valve.

The book doesn't mention what the resistance value should be, just that there should be continuity. Sorry.

[Elvis]

If it moves - it is good !

you may want to lube it with some drops of oil - but that's it.

Why a new one ? it's supposed to hum, that's how it works !

I can't find a description what kind of idle problem you have ?
(well, there have been at least 100 here so it won't be anything new)

test of the idle motor:
+12V to the center pin,
Ground to one of the outer pins makes it open or close completely.
You should hear a "clack" "clack" each time you change the Ground-Pin.
Just connect it for a second, NOT permanently !



The Wiring is new (NOS 1983 harnesses in the engine bay). I did the second test in my previous post, these were my results.
- 1st attempt - valve opened slowly and part of the way. Then closed slowly.
- 2nd attempt - valve opened quickly, did not close at all.

Through both attempts (and previously) the regulator was humming loudly and vibrating.

I might try to clean it, but more likely (because of the noise it was making), I'll just order a new one.

Thanks

[glockworks21]

For testing see info. below in italics. It's taken from K-Jet.org. It first tells you how to check the motor condition via a resistance check on the IAC connector pins. It then goes on to explain how to go after the mechanical end of it.

Dave did mention something about the connectors themselves sometime going bad as I recall. Check the wiring close to the IAC motor to be sure it's OK.



Another way to test the idle air motor is to measure the resistance with your multimeter. A good motor should read +/-20 ohms resistance between any two pins that are next to eachother and +/-40 ohms resistance between the two outside pins.

The idle air motor can be cleaned out if it is not too damaged. The most common way to do this is to detach the motor from the car and spray it out with carb cleaner. Fill the motor with carb cleaner and plug both openings in it. Shake it up and roll it back and forth in between your hands like you are making a ‘snake’ out of clay. You should hear it clicking back and forth. Repeat the cleaning process several times, drain the motor, and then allow it to dry for an hour or so.

source page: LINK: http://www.k-jet.org/articles/information/k-jet-debugging-guide/#41 (http://www.k-jet.org/articles/information/k-jet-debugging-guide/#41)



this one reads 10.5 on the pins next to each other and 21 on the outer pins..

?

Dave

[Bitsyncmaster]

this one reads 10.5 on the pins next to each other and 21 on the outer pins..

?

Dave

That is typical for the stock idle motor. The Volvo one is about twice that.

[Rich]

Thanks for the DMC-specific ISM resistance info, Dave. My reference page was generic.

Apparently there's nothing electrically wrong with this motor. No opens, no shorts.

Clean the valve internals twice more, using carb cleaner. Then check its operation again. Something's probably causing the valve to bind when the motor tries to move it.

[Bitsyncmaster]

Thanks for the DMC-specific ISM resistance info, Dave. My reference page was generic.

Apparently there's nothing electrically wrong with this motor. No opens, no shorts.

Clean the valve internals twice more, using carb cleaner. Then check its operation again. Something's probably causing the valve to bind when the motor tries to move it.

If the thermistor was not connected it would only close the the idle motor (just key on no start) about to 3/4 open. If the thermistor is below 5 Kohms then the idle motor will close almost all the way (about .1" left open).

I just bench tested this with a OEM idle ECU. I was not sure if it functioned the same without engine running but it does.

As I have always been saying the thermistor just limits how closed the idle motor would go. It has no other function. That is how the design provides a higher cold start RPM.

[82DMC12]

If the thermistor was not connected it would only close the the idle motor (just key on no start) about to 3/4 open. If the thermistor is below 5 Kohms then the idle motor will close almost all the way (about .1" left open).

I just bench tested this with a OEM idle ECU. I was not sure if it functioned the same without engine running but it does.

As I have always been saying the thermistor just limits how closed the idle motor would go. It has no other function. That is how the design provides a higher cold start RPM.

Hi Dave,

I was out of town this weekend but last night experimented a bit with trying to "jump out" my thermistor. If you recall, cold I am getting about 8.0 on the 20K scale and hot (fans on) about 0.85 when measuring between black/yellow and black/slate on the idle ECU inner plug.

I then pulled those two wires out of the plug and replaced them with a jumper so that the two pins on the ECU were joined. The results were inconclusive and I'm going to try again tonight.

What would joining those two pins do? Would it allow the idle motor to close completely, or only close to the "fast idle" condition you mention? I want to be 100% sure I am effectively ruling out the thermistor switch and the thermistor plug and all thermistor wiring up to the idle ECU so I don't keep chasing that ghost or needlessly spend all day replacing the thermistor, draining coolant, refilling, bleeding, etc.

Thanks a million!!!

[Bitsyncmaster]

Hi Dave,

I was out of town this weekend but last night experimented a bit with trying to "jump out" my thermistor. If you recall, cold I am getting about 8.0 on the 20K scale and hot (fans on) about 0.85 when measuring between black/yellow and black/slate on the idle ECU inner plug.

I then pulled those two wires out of the plug and replaced them with a jumper so that the two pins on the ECU were joined. The results were inconclusive and I'm going to try again tonight.

What would joining those two pins do? Would it allow the idle motor to close completely, or only close to the "fast idle" condition you mention? I want to be 100% sure I am effectively ruling out the thermistor switch and the thermistor plug and all thermistor wiring up to the idle ECU so I don't keep chasing that ghost or needlessly spend all day replacing the thermistor, draining coolant, refilling, bleeding, etc.

Thanks a million!!!

The jumper lets the idle motor close to almost fully closed (about 0.1" still open). I don't know why the stock idle ECUs don't close it fully. Just watch is for about 30 seconds with the key turned to on and engine not running.

[82DMC12]

The jumper lets the idle motor close to almost fully closed (about 0.1" still open). I don't know why the stock idle ECUs don't close it fully. Just watch is for about 30 seconds with the key turned to on and engine not running.

OK great, so it sounds like the test I am attempting to do will simulate a thermistor in its "hot" state and will force the idle motor to the most closed state in regards to normal engine operation.

If my idle is still elevated with this jumper in place, then I have effectively ruled out the entire thermistor circuit, do you agree?

By the way, thanks for all this detailed information on the idle circuit. This information would be hard to find if it weren't you staying active on DMCTalk!

[Bitsyncmaster]

OK great, so it sounds like the test I am attempting to do will simulate a thermistor in its "hot" state and will force the idle motor to the most closed state in regards to normal engine operation.

If my idle is still elevated with this jumper in place, then I have effectively ruled out the entire thermistor circuit, do you agree?

By the way, thanks for all this detailed information on the idle circuit. This information would be hard to find if it weren't you staying active on DMCTalk!

Yes the ECU will think the engine is hot with that jumper. If it does not close than I would suspect the idle motor is damaged on the valve.

[82DMC12]

Yes the ECU will think the engine is hot with that jumper. If it does not close than I would suspect the idle motor is damaged on the valve.

Hmm I am going to have to test this! I'll try it cold without the jumper but everything plugged in, then I'll try it with the jumper to see if it closes any differently.

[82DMC12]

Hmm I am going to have to test this! I'll try it cold without the jumper but everything plugged in, then I'll try it with the jumper to see if it closes any differently.

Here is what I found when following this test procedure.

First I checked the 20K ohm value between Black-yellow and Black-Slate on the "inner" plug of the idle ECU (the one with only four wires on it).

Stone cold engine but hot summer day in my garage - 4.xx on 20K scale (indicating the thermistor is warm enough due to ambient that no "fast idle" is required)

Test 1 - I pulled out the idle motor but left it plugged into the black plug. I turned the key to ON (Position II) and quickly went back to look at the motor with a flashlight. I saw the "gate" inside had opened completely and after a few seconds it began to retract towards the left (as installed). It closed until there was but a small space the thickness of a slotted screwdriver blade remaining for air to go though.

Test 2 - I then turned off the key and removed the black-yellow wire from the white plug (insert a small jeweler screwdriver under the female spade and push up while pulling the wire out to release the lock clip). This resulted in open-circuit and lack of continuity to the thermistor. I repeated the test and found the motor will only close about half way.

Test 3 - I then removed all four wires from the white plug and made a new jumper that connected the terminals that the thermistor goes to on the idle ECU itself, then plugged in the other two wires (black-green and white-slate) being very careful that they were secure and cannot touch. I turned the key to ON and checked the motor - exact same behavior as the first test, closing nearly completely.

I reinstalled the idle motor and then ran the car up to normal operating temperature with the jumper installed. After about 20 minutes of idling my idle started to climb as I have been trying to solve for weeks now (thermistor totally removed from the circuit so now I know the thermistor is not my issue!). I pulled out the motor once again (quite hot by now!) and repeated Test 3 and found the motor closed to the same nearly closed position even though the idle had been about 1,000 RPM and erratic. So I believe I have effectively ruled out the idle motor itself as defective when both cold and hot.

Thoughts on my logic?

[Bitsyncmaster]

Try hot gluing the deceleration valve closed.

[82DMC12]

Try hot gluing the deceleration valve closed.

That's my next plan - actually first I might run a temporary ground from the Idle ECU directly to the battery, a temp ground from the RPM relay to the battery, and a temp ground from the idle speed microswitch directly to the battery. Maybe also from the ignition ECU to the battery. That should totally rule out any kind of weird grounding problem.

[David T]

If the idle speed is increasing and you have ruled out the idle motor, air is getting into the motor somehow. The throttle plates are moving, the decel valves are leaking, somehow more air (and fuel) is getting in. It can also be the advance is kicking in. Tape off the vacuum hose going to the distributor.

[82DMC12]

If the idle speed is increasing and you have ruled out the idle motor, air is getting into the motor somehow. The throttle plates are moving, the decel valves are leaking, somehow more air (and fuel) is getting in. It can also be the advance is kicking in. Tape off the vacuum hose going to the distributor.

Thanks David. The more I think about it, I think there are only a few possibilities remaining. As you said, this is a mechanical system and there are only a few ways this problem can occur. I believe I have ruled out the idle motor. The throttle plates are NOT moving because they are under total tension and unable to move without pressing the gas pedal. My current theory is the springs are getting hot and losing tension thus allowing some air to leak through the decel valves. I am going to seal them closed with a hot glue gun this weekend and see what happens. If the idle keeps coming up but the hot glue seal is unbroken, then it has to be something else.

Other possibilities:
1) somehow the ground to the Idle ECU, idle speed motor , or idle speed microswitch is getting interference for a bad connection as the car warms up
2) The idle motor is somehow crapping out as it gets hot

I have already pulled off the vacuum hose from the distributor vacuum advance while in the elevated idle condition and there is no vacuum at that time.

One thing is for sure - I will be the expert at DeLorean idle by the time I figure this one out!

[Rich]

Other possibilities:
1) somehow the ground to the Idle ECU, idle speed motor , or idle speed microswitch is getting interference for a bad connection as the car warms up
2) The idle motor is somehow crapping out as it gets hot


Picking up on your Other Possibility #2.

Consider adding this issue to your potential problem list: The top of your ISM has a crack/leak in it? The leak may change with operating time/temp?

Here is a video posted by jawn101 demonstrating one way it can behave with this failure: https://www.youtube.com/watch?v=JEZbVVOiPfc

It's not obvious that air leaking into the ISM connector or the top of the ISM body can create a fast or variable idle speed problem. But it can.

Jawn101's thread which is partially about this is here (https://dmctalk.org/showthread.php?17869). You can pick up at about Post #50, also noting another forum user chiming in saying their ISM failed similarly. You'll notice Jon (jawn101) started out chasing the decel springs as a cause of an idle problem...

I've had my original ISM go bad in a similar way - a vacuum leak near the connector base (I was able to patch the leak, no need to replace the ISM so far).

[82DMC12]

Picking up on your Other Possibility #2.

Consider adding this issue to your potential problem list: The top of your ISM has a crack/leak in it? The leak may change with operating time/temp?

Here is a video posted by jawn101 demonstrating one way it can behave with this failure: https://www.youtube.com/watch?v=JEZbVVOiPfc

It's not obvious that air leaking into the ISM connector or the top of the ISM body can create a fast or variable idle speed problem. But it can.

Jawn101's thread which is partially about this is here (https://dmctalk.org/showthread.php?17869). You can pick up at about Post #50, also noting another forum user chiming in saying their ISM failed similarly. You'll notice Jon (jawn101) started out chasing the decel springs as a cause of an idle problem...

I've had my original ISM go bad in a similar way - a vacuum leak near the connector base (I was able to patch the leak, no need to replace the ISM so far).

Rich,

Thanks for thinking about me! I did perform a smoke test with both a cold engine and a hot engine and looked specifically for that type of leak. Negative. My next two tests are:

1) Run a temporary ground for the idle ECU, idle microswitch, RPM relay, and perhaps also the ignition ECU (harder to tap into though) so I can totally eliminate a grounding issue that could be crapping out when the engine gets hot

2) Got a hot glue gun today so I'm going to temporarily glue to decel valves closed and see if that helps. If it does, I know my problem is the decel springs though they look visually OK. Sounds like there is some ability to tighten the springs down too. Maybe when I was cleaning the butterfly I disturbed the calibration of the springs.

Hopefully get to this over the weekend - it's been oppressively hot in Kansas City this week (heat index over 100)

[82DMC12]

To anyone reading this in the future, I did hot glue my decel springs closed and it did NOT fix my creeping up idle when hot. So I think it's safe to say if your springs look OK and they do not appear collapsed with coils touching, they are not the problem.

I did eventually solve my idle issues but they coincided with a tachometer problem related to white/slate off the impulse coil making a bad signal. Either the impulse coil was bad or the tach fly lead was bad (I replaced both at once). That solved the tach. I also re-set my throttle arm while I had the throttle body out and on reinstallation my idle was fixed too.