944S2 at Idle

[Guest]

Hi All

Does anybody know why my 1989 944S2 sounds like an old nail at idle and misfires up to approx 2000 rpm?. It runs smoothly above this figure but will often stall when it goes back to idle speed. (at junctions etc). There's a strong smell of petrol after the morning startup, lots of coughing and spluttering (not me- the CAR!) and then it runs as above. It will stall if you're too heavy footed when moving off from standstill too..

Fuel was about 1/4 full, mileage is 126,000 and it has a full service history. Fuel pipes were replaced about 4 years ago.

Cheers

 

[rob944s]

I could be many things a ht lead sounds like its failing to me, have you checked the plugs after a cold start you may find a wet one this will indicate the lead or plug that is failing.....are you still having problems?

 

[Indi9xx]

lots of options...

Low rpm rough running could be...

cam timing
broken valve spring or a valve not sealing so well/bent
high or low fuel pressure
bad distributor cap, leads, rotor arm or plugs
bad low end track in the airflow meter
even a blow in the cylinder head gasket between two cylinders

I have even seen ECU's to be failed in this state, often following prolonged high fuel pressure issues burning out the injector drivers within the ECU (AKA DME but not to be confused with the DME relay)

Actually... thinking about it.. even the DME relay often fails in this condition due to the nature of its opperation of overlapping pulses.

Check the above, or even get a specialist to check them out for you... but do not let it continue running like this

 

[AndrewS]

ORIGINAL: bargeboy

Hi All

Does anybody know why my 1989 944S2 sounds like an old nail at idle and misfires up to approx 2000 rpm?. It runs smoothly above this figure but will often stall when it goes back to idle speed. (at junctions etc). There's a strong smell of petrol after the morning startup, lots of coughing and spluttering (not me- the CAR!) and then it runs as above. It will stall if you're too heavy footed when moving off from standstill too..

Fuel was about 1/4 full, mileage is 126,000 and it has a full service history. Fuel pipes were replaced about 4 years ago.

Cheers

Hi,

John has mentioned most of the possibilities. I would also add the ISV (Idle Stabilisation Valve). When the car is cold, a sensor transmits a signal to the ECU to alter the fuel mixture (richen) to enable the car to run smoothly when cold. The ISV is also controlled by the ECU and alters the air introduced into the inlet manifold (after the metering unit - AFM) to help achieve the correct idle. You could have a problem with either the sensor or the ISV.

Again, very difficult to diagnose based on a description and the above must only be considered a possibility. Your note about stabbing the throttle suggests it might be this or AFM related.

As John has also suggested, you need to get this resolved quickly as unburnt fuel in the combustion chambers will disolve the oil film on the bores and potentially accelerate ring and bore wear. Not good. :-(

Regards,
Andrew