Need help from any 10v gurus..

[mcandmar]

Trying to help a forum member with a 10v coupe, NG engine. Car has recently had a head gasket failure which was replaced and the head rebuilt.

First problem is the car failed an emissions test, co was very low ~0.13 but the HC was way too high, over 1400ppm, limit is 750. Found two problems, first being the screw on caps were left on the spark plugs so the HT leads were sitting loosely on top of them, fairly sure this is the cause of the huge HC reading due to misfires. Also found somebody had screwed in the throttle body stop to raise the idle meaning the idle switch was not being contacted, reset that to factory settings and confirmed the idle and WOT switches are working properly.

Second problem is the engine will not idle unless the revs are held over 2000rpms until it has warmed up, when fully warm it will idle at 900rpms, but still runs very lumpy. Mixture setting on the metering head had been messed with so without any way to set it up correctly or confirm if there is an issue with the flap position sensor we swapped it out for a known good unit. Made no difference and the idle is still as lumpy as hell warm or cold. Gave the ISV a good clean out for good measure, and the spark plugs come out very clean so if anything it is running lean not rich.

The big problem is the engine will not start when warm, confirmed the issue is due to no spark. If we disconnect the engine temp sensor we have a spark and the engine starts again. According to the Bentley manual it is a two pin sensor, each provides a resistance range according to temperature, one pin is used for the fueling ECU, the other for the Ignition Unit. Confirmed the sensor is working and giving out values that match the range in the manual. But for some bizzare reason when plugged in we have no ignition. Plug in a spare sensor that is at room temperature and we have ignition and the engine starts

I am completely and utterly stumped on this one, makes no sense whatsoever. Has anybody seen anything like this or have any ideas?

And before anyone asks Vagcom will not talk to it and i didnt have my LED tester with me to check for fault codes. Will check next time..

[Nuvo]

There is a good chance that the lumpy/erratic idling will be caused by a tear in the rubber pipe that connects to the ISV.
The hole is normally seen around the elbow of the ISV pipe.

[Mikes2]

Have you been able to try a spare ignition module.

Is the wiring from the 2 pin sensor to ignition ok - should be less than 0.5 ohms

The ignition module must be killing the spark because it's seeing something it doesn't like. If the sensor is giving the correct outputs as you say, the module itself must be throwing a fit.

[Avantus]

try disconnecting the ISV and see if it runs (al be it higher) idle. Check for airleaks, and a metering head that has been messed with usually is bad news... they should stay untouched.

[mcandmar]

I managed to pull the ISV breather pipe out when removing the Idle valve, should have had a hose clamp on it but it fitted back on tight when i pushed it back in. Problem is you cant see down there under the manifold on these motors.

Next plan of action is to try and find a replacement ignition unit to swap out and see if it cures the warm no start. From what i've read the injector seals are known to tear and leak so i plan to split the manifold next time to have a look at the injectors and ISV pipework hidden down there.

Can anybody confirm if the Ignition and Fueling ECU's are two separate units or one box. Also i assume its located on the back on the heater unit as per 7A/S2?