Idling Problem

[casewolf]

Hi all!

I think this is my first post here and before all I would like to thank the community for contributing so much knowledge that already helped me before.

My car is a 1993 S4 (the early model without Brembos) in BRG, LHD and I live in Germany. I own the car since last year, January, it came from Belgium before.

The car is stored in garage during wintertime from November on and 'reactivated' in March. This winter, I installed Chip #3 from Markus Freudhöfer, packed in a De-Cat-Pipe, K&N-Filter and the so called 'Ram-Air' induction + a BOV. The test drives in early March went well and I am fully confident with the cars performance and sound. I use the car during the summer season regularly (2-3 Times a week).

Now I got a strange issue I haven't found searching here: Yesterday, after riding it for half an hour (smooth accelerating, tender throttling, no "digital" driving) I put it into garage and took it out in the evening again, as I was heading for a business meeting. As soon as I started, I noticed some hesitation and a tiny bit of stalling when playing with the throttle, not too bad, but noticable. Something that hasn't been there before. When I reached the city (some 5-10 minutes) I switched AC off, as it was still on from the last ride. Doing this, I was waiting for the traffic lights to get green again, in idle. When I switched the AC off, RPM dropped to roundabout 200rpm and the car eventually died. Started the car again, all was fine. Since that I was a bit scared, I haven't tried to reproduce the situation and now it is raining here, so I use the time to get some idea about the reason for this behaviour.

Could it be the dreaded IAC (Idle Air Control)-Valve? Some electric fault? Petrol pump problems?

Concerning the performance of the car: It's very quick, revs up nicely (no misfiring) and sounds ok for me (including the usual bangs from unburnt fuel when over 4000RPM and playing with the foot).

Anybody an Idea? Ah: I have Freescan and EspritMon here and working! No CEL occured. Maybe I should point out, that I have washed the car the same day and some water may have dripped into the engine bay...

Edited March 26, 2010 by casewolf

[casewolf]

Noone? Or ist this a common problem?

[Jonathan]

Common, the compressor has a clutch that engages to the pulley on the engine which loads the engine up slightly - hence drop in RPM.

A common cure is to disconnect the battery (when the car is switched off) and leave for a few mins (this wipes the ECU volatile memory).

Then re-connect the battery and go for a drive WITH the aircon switched on, this makes the ECU re-learn the engine particulars with the extra loading of the aircon clutch engaged and can help stop stuttering at idle as the ECU learns there is more load.

Give it a go !

[casewolf]

Ah, thanks Jonathan. As I nearly always disconnect the battery (not driving every day) - the problem disappeared after the next ride. Thanks again!

[matk]

The problem with always disconnecting the battery is that the ECU has to go through it's start up learning parameters EVERY time you reconnect the battery. Now I'm a carbs man, so not an expert, but IIRC that means about 30 mins of driving every time?

Is that good for the car?

Would it be better for you to keep the battery connected with a trickle charger?

[Riddlemr2]

Yep, you don't want to reset the ECU too often, but I find that doing so in the Spring gets it ready for Summer, then doing it again on a cold day in the Fall makes it run better in the Winter.

[Splodge s4]

I find that doing so in the Spring gets it ready for Summer, then doing it again on a cold day in the Fall makes it run better in the Winter.

I've noticed the same