Vectra C poor idle

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Hi guys, great site you have here, first time poster here goes.

Vectra C 1.8 model year 8/03, 78K drives well, sound engine, no excess blowby or other nasties.

Just sold the car and it came back 2 days later with the new owner saying idle speed going up and down, almost stalling but recovering.

Removed the throttle body, had some muck around the throttle plate seat and cleaned with carb cleaner manually moving the throttle plate, unblocked the 1mm bleed screw in the base of the throttle body.

Now the idle speed to consistant but the idle is rough as the proverbial badgers backside

Hmm....inspected the system to check for accidently removed pipes causing an airleak, nothing found. Removed the throttle body again to check for split gasket, nothing found , refitted....still a rough idle.

I had a similar problem with a VW Beetle and did a throttle body re-learn and this cured the issue, so I went into the Vectra ECU with a borrowed Snap-On scanner thinking maybe the throttle body needed a re-learn only to find this function isn't available...maybe only for later Vectra's?

Now the cars drives fine over 1500 rpm, no stutters, flat spots, just drives well, but under 1500 rpm there is misfire and jerkiness to the drive...similar to a massive airleak. I've sprayed all around the engine bay for air leaks with carb cleaner and nothing, the rough but consistant idle remains just that.

OK, I then started checking the live data using my Gendan scanner and find the MAF grams/second is too high at around 6 grms/s at idle, I'm expecting this to be 1.6 grms/s or there abouts. Fitted a new MAF and the results were the same....I didn't think the MAF was at fault as I did the old trick of removing the MAF connecter and the nothing changed. I'm guessing she running so rough it needs this additional air to maintain the idle speed?

Long term fuel trim is...wait for it -100.....but I'm not getting any codes....so the ECU is trying to lean her off when at the same time the MAF is saying the engine is injesting more air than normal.

Lambda sensor is switching.

EGR valve not stuck open, I removed it and checked.

Pulling the lambda connector makes no difference to the idle as a check so it goes onto the limp home map nor does pulling the camshaft sensor, even pulling the throttle body connector gives me a change in idle speed but still with a rough idle....even pulling the air inlet from the throttle body so unmetered air is entering the engine still gves me the same rough idle.

I pulled the injecter connectors one by one, all were firing and it appears I dont have a cylinder down on compression as the drop was the same on all pots?

I checked for loss of earth for the MAF and ETC (engine temperature coolant) but earths seems fine, there was a problem with XE engines ECU's loosing their earth but then the data would of been nonsense I'm guessing for the MAF and ETC.

So that's it...I got a used throttle body coming tomorrow but I can't see that being the issue somehow...but hey I'm getting desperate....ECU don't think so the cars drives fine when the throttle plate is opened.

any ideas gentlemen?

One thing did occur to me do I need OP-COM to so a throttle body re-learn and thats why the Snap-On can't do this feature?

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Ohh, shes a petrol!

[paul9]

If you removed the MAF connector and nothing changed, would that not point towards faulty wiring from the MAF sensor to the ECU? If there is a bias voltage on the MAF, then could that explain a high airflow reading, if the MAF isn't properly connected? Is there a fuse in the MAF line to the ECU? Does the reading from the MAF change in a sensible manner when you rev the engine, or restrict the air into the air intake?

[iconic]

If you removed the MAF connector and nothing changed, would that not point towards faulty wiring from the MAF sensor to the ECU? If there is a bias voltage on the MAF, then could that explain a high airflow reading, if the MAF isn't properly connected? Is there a fuse in the MAF line to the ECU? Does the reading from the MAF change in a sensible manner when you rev the engine, or restrict the air into the air intake?

Hi Paul, thanks for the reply,

yes, MAF readings at zero and full load at 4k rpm looking fine.

I have just had her on a gas analyser and she is running so lean its amazing she runs, gota feeling my Lambda sensor is lying, going to check a few more things around the this area.

cheers

[paul9]

You said you checked the EGR valve, but did you check the idle air control valve solenoid?
Otherwise, I think the downstream Lambda sensor could be faulty, that can cause the long term trim to peg out at extreme values.
I have seen one case where a twisted cam shaft caused lean running, but that was a rare extreme, and on a V6.

[iconic]

You said you checked the EGR valve, but did you check the idle air control valve solenoid?
Otherwise, I think the downstream Lambda sensor could be faulty, that can cause the long term trim to peg out at extreme values.
I have seen one case where a twisted cam shaft caused lean running, but that was a rare extreme, and on a V6.

Cheers for reply Paul

She has a throttle body...there is no idle control valve, the throttle body controls idle speed.

Downstream lambda sensor (post cat) does not control fuel trim, the downstream is there for a feedback for cat' eff' check on this vehicle....a few newer cars have a small amount of trim applied by the post cat' sensor.

Twisted cam, do you mean cam timing timing being off, or the actual camshaft twisted? I've never seen that in 40 years around cars, that amazing.

cheers Paul


search goes on

[paul9]

Yes, it was a twisted camshaft, which had the effect of throwing off the timing by a notch and eating its bearing. Chain timing. The other side of the V engine ended up getting the wrong amount of air because of it.
The engine still ran smoothly.
https://youtu.be/K-UlvBZ95Jo?t=45m31s

[iconic]

Yes, it was a twisted camshaft, which had the effect of throwing off the timing by a notch and eating its bearing. Chain timing. The other side of the V engine ended up getting the wrong amount of air because of it.
The engine still ran smoothly.
https://youtu.be/K-UlvBZ95Jo?t=45m31s

Interesting video, and theres me thinking only Volkswagen have issue with broken camshafts