Rough Idle, Chugging On Accel – Lambda System Not Working

[klaatu42]

Had to repost this thread, because the first one I posted is throwing a 403 error.

Hi. I'm scratching my head a bit on this one (but admittedly that doesn't take much).

11633 suddenly started shuddering and chugging at a traffic light and I drove carefully, white knuckled home with very little power when starting up from each subsequent stop. My idle is now very randomly up and down (not seeking, nor in any noticeable pattern) and it really wants to die when I try to start moving or accelerate (I've taken it around the block a few times here and there to test).

The odd thing is, after finding that my frequency valve bulkhead connector female pins were so loose they were probably not making contact at all, I found that I could completely disconnect or connect it with zero effect at all on idle. I then noticed the same thing when unplugging my O2 sensor (no effect at all), and was further surprised when I was able to disconnect and reconnect the whole Lambda ECU with absolutely zero effect.

Am I right in thinking that depressing the full throttle enrichment dipswitch should alter idle? Mine doesn't.

Replaced Lambda relay with no effect.

The grounds and power to the ECU seem to be fine.

:banghead:

Video illustrating the erratic idle (turn your sound up): https://www.youtube.com/watch?v=YA0oI4pz-5M

[sdg3205]

Make sure the female spades for the relay pins on the underside of the lambda relay socket have not backed out. The lambda relay is not a standard relay. Are you using a lambda specific relay?

[klaatu42]

Make sure the female spades for the relay pins on the underside of the lambda relay socket have not backed out. The lambda relay is not a standard relay. Are you using a lambda specific relay?

Thanks for the reply. Yup, I checked the pins when I did the swap (with new lambda specific relay). No effect after changing it. Tempted to change it back to remove that variable, but the old one is quite crusty.

[sdg3205]

Check the ground for the lambda system that runs off the RH intake plenum near the back. It's off the side. Is that in tact? It should be bolted on with a ring terminal then becomes a spade terminal junction.

By back I mean closest to firewall :)

[sdg3205]

Also have you checked the fuse?

[klaatu42]

Check the ground for the lambda system that runs off the RH intake plenum near the back. It's off the side. Is that in tact? It should be bolted on with a ring terminal then becomes a spade terminal junction.

By back I mean closest to firewall :)

Thanks. Justin from Wells Auto also felt this could be the culprit. I've checked it and the connector that it leads to a couple inches back, but I'm wondering if it is disrupted somewhere further along, and I'm not sure exactly where that ground ultimately goes in the Lambda system. I verified the grounds on the Lambda ECU connector, and the ring ground below the connector, and they all appear to be sound.

[sdg3205]

If you are getting 12v at the relay socket and all your grounds are good my guess is there is an issues at the bulkhead molex connectors. Pins can back out or corrode. Do you have the bulkhead pin schematic? You should find it here no problem, then proceed to clean the male and female pins at the bulkhead with sandpaper and alcohol. It's time consuming but effective.

[klaatu42]

Also have you checked the fuse?

Removed, visually inspected each fuse and socket, and tested each fuse as good.

The Lambda ECU connector is getting power.

[klaatu42]

If you are getting 12v at the relay socket and all your grounds are good my guess is there is an issues at the bulkhead molex connectors. Pins can back out or corrode. Do you have the bulkhead pin schematic? You should find it here no problem, then proceed to clean the male and female pins at the bulkhead with sandpaper and alcohol. It's time consuming but effective.

Thanks. I removed and inspected all of the bulkhead connectors and they are all super clean and tight, with the exception of the aforementioned frequency valve connector, which had female sockets that were incredibly loose.

I'm starting to wonder if the little chipmunk friends I feed outside, and who come to the garage to get me when I forget to feed them, decided to have a little chew on a wire somewhere... I originally ruled that idea out because the problem started near the end of a long drive, but a partially chewed wire could certainly heat up and fail.

[Bitsyncmaster]

Does the FV buzz? The "lambda" relay switches power to the FV and the lambda ECU with separate pin outputs. If the FV does buzz, both the FV and ECU are getting power.

[Jonathan]

When you said "shuddering", it made me think of what happens when you get the engine wet and a spark plug well has water in it. Assuming there's something else at play here though. Check to see that your spark plug wires are all clipped in properly anyway.

Could you post a video or some pictures of the engine bay with the cover/louvres raised? Maybe one of us will spot something out of place for you.

[Bitsyncmaster]

I did not see or hear anything out of the ordinary on your video.

[sdg3205]

I did not see or hear anything out of the ordinary on your video.

I couldn't get sound but the idle looked fine.

If the WOT switch and unplugging the FV did nothing to affect idle i bet his car is tuned to run open loop.

[David T]

I couldn't get sound but the idle looked fine.

If the WOT switch and unplugging the FV did nothing to affect idle i bet his car is tuned to run open loop.

Which raises the question, "Was the Lambda system working BEFORE this problem?". We don't know. Sounds like it wasn't. Maybe you suddenly developed a vacuum leak? Is the plug there over the mixture screw? First order of business would be to get the frequency valve to buzz. Then check the duty cycle and if necessary adjust the mixture screw.

[sdg3205]

I think you're right

[klaatu42]

Does the FV buzz? The "lambda" relay switches power to the FV and the lambda ECU with separate pin outputs. If the FV does buzz, both the FV and ECU are getting power.

Well, I thought it was buzzing all along, but it turned out to be the idle speed regulator humming!

I can't seem to get it to buzz by turning key to 2. Zero voltage going to either pin on its connector.

But... When the engine is running it gets just over 14V on one pin and the other fluctuates up to 2V.

When I pull the Lambda ECU connector I see that it is receiving no power until the engine is actually running (13.9V).

[Bitsyncmaster]

Well, I thought it was buzzing all along, but it turned out to be the idle speed regulator humming!

I can't seem to get it to buzz by turning key to 2. Zero voltage going to either pin on its connector.

But... When the engine is running it gets just over 14V on one pin and the other fluctuates up to 2V.

When I pull the Lambda ECU connector I see that it is receiving no power until the engine is actually running (13.9V).

The lambda relay gets turned on my the RPM relay. So just like the fuel pump, the lambda system only gets power when the engine is running.

You need to get a dwell or duty cycle meter onto the FV to verify your mixture is set correctly.

[David T]

For troubleshooting purposes refer to D:04:12 for a simplified schematic of the wiring of the Lambda system. A good place to start would be the ECU module. Pull the plug and verify power, grounds, switching and wiring. Also refer to D:04:15 5 A-E. By applying power (1.5 DCV) or grounding the O2 sensor lead you should see the correct values on your dwell meter. Read the system repair notes, specifically #3 to power the Lambda system for testing purposes. The Lambda system isn't going to work till you can make it do what it says under "Pulse Ratios #5 A-E. If you can force the readings but it won't fluctuate as it should under A, the O2 sensor is probably no good.

[klaatu42]

Which raises the question, "Was the Lambda system working BEFORE this problem?". We don't know. Sounds like it wasn't. Maybe you suddenly developed a vacuum leak? Is the plug there over the mixture screw? First order of business would be to get the frequency valve to buzz. Then check the duty cycle and if necessary adjust the mixture screw.

It wouldn't be like me to find an issue that is causing a symptom so I'm sure you are right... It likely wasn't working and was tuned to run open loop without bothering to physically disconnect anything. There is a plug above mixture screw. I'm probably chasing my tail going down the Lambda route.

[klaatu42]

I couldn't get sound but the idle looked fine.

You can only hear the issue. It's a seemingly completely random fluctuation, not all all like seeking. I'm editing together an updated video with some driving. Should illustrate things better.

It's so intermittent and random that it must be electrical. I can pull away from a stop with no trouble whatsoever and at the very next one, less than a minute away, I can barely get moving, then the next fine again.

The hotter the engine gets, the worse/more pronounced it seems to be. In fact, when I took it out just now to shoot the video, at first I thought that something I had done had fixed it, but it just got progressively worse the further I went.

[sdg3205]

Ahhhh. Sounds like your coil may be on the way out!

[Bitsyncmaster]

Ahhhh. Sounds like your coil may be on the way out!

Usually heat related failing may be the ignition coil or the pickup coil. The pickup coil really needs good connections so check that two pin connector from the pickup coil that goes into the "firewall". Mine was so bad, I just cut the connector off and soldered the wires.

[klaatu42]

Ahhhh. Sounds like your coil may be on the way out!

Aha. I did have some slightly melty wire insulation near the top of the coil. Everything seemed sound, though.

I'm going to go after the coil right away, but since I already put this together, here's a more complete video (audio is essential). It's subtle, but the random rev-rev-purr-rev-purr-purr came at the same time as the low power during accel issue:

https://www.youtube.com/watch?v=JgG7_VxjMDs

[klaatu42]

Replaced a burned connector (the white/grey wire) on the coil, and found that it was also very loose. Replaced, snugged it up, and of course it's still exactly the same, lol. I have a tach connected to that pin and I do recall it going blank once while driving about a month ago, so I'm sure that connection was a bit wonky for a while.

I have a UF2 coil ready to pick up in town, but despite Partsource saying it is compatible, I'm skeptical. It will take me days to get a Bosch, so I was going to try out this UF2 to see if it at least fixes the issue until the Bosch comes.

Driving season is too short in Sudbury, ON and British Car Day is coming up soon, where I plan to attend with my Sinclair C5 on the luggage rack, so I'm hoping I can figure this out soon. Pretty sure the lambda system route is a red herring and likely wasn't working all along.

46082

[Autoboys]

Just an observation of something you mentioned. This may sound crazy but take your are cleaner off and check the box and air filter for obstruction. You did mention our Canadian tree rats(chipmunks). It could be possible they made a nest in the air filter box? Don't ask!

The second I would recommend would be to run the car at night with the engine light off and see if you have any arching from the ignition wires. Sounds like you checked most items but haven't touched these. I had a similar issue a few years back with old stock wires and only caught it while checking it at night. It was an intermittent 1st of July!!

Hope you make it to Bronte!

[klaatu42]

Just an observation of something you mentioned. This may sound crazy but take your are cleaner off and check the box and air filter for obstruction. You did mention our Canadian tree rats(chipmunks). It could be possible they made a nest in the air filter box? Don't ask!

The second I would recommend would be to run the car at night with the engine light off and see if you have any arching from the ignition wires. Sounds like you checked most items but haven't touched these. I had a similar issue a few years back with old stock wires and only caught it while checking it at night. It was an intermittent 1st of July!!

Hope you make it to Bronte!

Thanks. It wasn't the coil. :/ I swapped it, then started rejoicing when the idle was cleared up and I was able to do a lot of stop/starts without any issue. It was literally when typing out the word "eureka" on my phone that the idle suddenly went south again.

I haven't had much time to look at this recently, but I'm hoping to again soon. My next port of call is exactly what you are suggesting –*arcing or other plug/wire issues. It should have been my first thing to check, but I went way down the wrong road (I think) trying to diagnose the lambda system issue.

[David T]

Thanks. It wasn't the coil. :/ I swapped it, then started rejoicing when the idle was cleared up and I was able to do a lot of stop/starts without any issue. It was literally when typing out the word "eureka" on my phone that the idle suddenly went south again.

I haven't had much time to look at this recently, but I'm hoping to again soon. My next port of call is exactly what you are suggesting –*arcing or other plug/wire issues. It should have been my first thing to check, but I went way down the wrong road (I think) trying to diagnose the lambda system issue.


It is rarely the coil unless it is not the original one. If the idle is good on startup and during warm up and then gets bad it is probably the Lambda system. Once the motor warms up the Lambda system is supposed to go into "closed loop". If it isn't functioning as it should the idle will be bad.