JShutterbugF

I am going to do a tune up on my car and I'm having a problem of stalling when the car idles. I have already had the battery and alternator checked and they are ok. Just looking for some advice for a jumping off point.*The RPMs drop really low and then it dies sometimes when I brake quickly. It seems to be running very rich. Sometimes it does the opposite and revs really high. The problem sometimes improves with a full gas tank and when it restarts, the exhaust smells pretty strong. Anyone had a similar problem? Fuel filter maybe? Vacuum problem? Advice is very much appreciated.*

peanut

Hi and welcome to the forum.
Sorry to hear you have some problems with your 944 .
It would help a lot if you tell which model and year you have .

First thing you'll need is a decent workshop manual. These are complex cars as no doubt you've realised.Do a search on google there are plenty of online manuals you can download.
Alternatively refer to Clarkes garage online workshop manual and guide http://www.clarks-garage.com/

For a rough or undulating idle I would check the following
1. vacuum system leak (best done with a smoke test ....see youtube )
2. TPS( throttle position switch)
3. AFM air flow meter
4. Auxillary air regulator (idle speed stabiliser) don't be tempted to fiddle with the idle adjust screw which is set by Porsche
5. Faulty cold start system .
6. fuel injectors faulty or blocked or injector solenoids sticky from lack of use.
7. insufficient fuel pressure ( test fuel pressure )
If you asked me to guess I would check the vacuum system first which includes all the pipe lines, connectors,oil dipstick, oil filla cap, injectors, air intake hose, brake servo hose etc etc ..refer to vacuum schematic

BradS(IN)

I added some fresh, hi octane gasoline, and Seafoam, a gasoline additive, and so far, the idle is up and holding even after it is warm.

JShutterbugF

Thank you both very much! It's a 1990 944 S2. I have bought the seafoam and will definitely try it with some high test gas and see if it helps! Fingers crossed! Peanut, thank you for that link. It is very helpful! I wish I knew more about cars owning this one

peanut

if it frequently stalls under braking I would say its likely to be a vaccum system leak because your brake servo is operated by the vaccum system and it is all connected to your inlet manifold . See if the idle changes if you operate the brake when stationary

I wouldn't use seafoam on a fuel injected car myself. Bosche strongly advise against using it with their fuel injection systems. Injectors are designed to self clean whilst working. if they are gummed up then they will need a proper clean and test by a specialist .

The manufacturers claims of seafoam and others are all well and good but the fact is that all the fuel injectors contain very tiny fuel filters which can easily get blocked with the residue that gets lifted off the fuel pipes after the main fuel filter.

peanut

any luck yet ?

The other componant you need to check is the Air Idle valve it goes under various names but its a small valve that allows a flow of air to the inlet when the throttle is closed during idling. http://www.944online.com/cgi-bin/for...num=1269686778

4porsche4life

Sounds like thats pointing to a vaccum leak...