Porsche Enthusiasts Club Forum

Evening all
I'm having a problem with the 944, it packed up on me the other day and have since managed to get it running again but not as it should.when I start the car from cold it ticks over fine but as the car warms up the revs increase with it upto the point of where it ticks over at about 1200 rpm,when the car reaches full operating temperature it then starts to hunt or surge fluctuating between 1000 rpm to 1600 rpm every few seconds or so ,if i remove the vacuum pipe from the fuel pressure regulator it stops hunting but still ticks over at around 1200 rpm , if I remove the vacuum pipe from the throttle body and plug the nipple coming from the throttle body this has the same effect.i have tested the fuel pressure along with the fuel flow and all seems to be ok,has anybody else had similar issues ? Could it be the fuel pressure regulator or the throttle body or maybe the tps ?
Any help resolving this would be much appreciated

Tel

Looks like you're chasing a vacuum leak or the idle control valve is faulty.

Don't think it's the TPS as that limited my revs to 1600 as it doesn't switch from the idle map to WOT map.

I'd check each and every vacuum hose & remove the intake manifold to get to the ICV underneath.

AFM perhaps??

I'd go with Delux Air leak &/or ICV The pipe work to the ICV is 'orrible & needs careful scrutiny.

Thanks for the replys.
I've been looking for an air leak but can't find one, I've checked all the vacuum pipes and sprayed carb cleaner whilst the engine is running but dos'nt make any difference . I tested the icv whilst it was off the car a few weeks back and it seemed to work ok but I am not ruling it out and I do have a spare.
When the car broke down the idle started surging between 1000 rpm and 1600 rpm for a few minutes and then started coughing and spluttering with no throttle response and I could hear the dme relay clicking like mad and then it just died,each time I cranked it over it was trying to start but just wouldn't ,it was as if it had ran out of fuel. I removed the dme relay and replaced with a jumper wire but that made no difference, I've checked the pump and all seems ok and done a flow and pressure test and all came back ok. I removed the fuse to the fuel pump and cranked the engine over to see if I had tachometer bounce and I did so I replaced the fuse turned the car over and it started and runs fine until it gets up to temperature and that's when it starts to surge but dos'nt cut out now,I can hold the revs at any range and it's fine it's only at idle, so I'm a little baffled now as to what it could be ?

I wonder if it's the DME temp sensor? Thats the front temp sensor under the intake with the blue plug.

I did wonder the same but I did replace it only 6 months ago

So today I got the the car in the workshop and ran some tests
1 . Unplugged the icv and connected a live and earth directly to the icv and it opened and closed as it should , plugged it back in and turned on ignition and I can feel it buzzing away, but if I unplug the icv whilst the engine is running it makes absoloutley no change to how the engine runs ??
2 put a jumper wire between terminals b&c on the diagnostic plug and all this did was increase the the rate at which the rpm fluctuates, I then tried to adjust the idle on the throttle body and pretty much made no difference to the idle apart from increase the rate of the fluctuations ,so I wound the screw back in to where it was.
3 removed throttle body and cleaned, checked that I could hear the micro switch on tps click and it did,
Although recently the tps was adjusted and is pretty worn I would say as I had to file out the screw holes to get the micro switch to make contact , if I unplug the tps whilst the engine is running the the rpm rise to 2000 rpm and sits there without any fluctuations until I plug it back in again, is this my problem ?
4 checked all vacuum pipes and can't seem to find anything wrong there
5 checked afm and retracked even though it looked good and don't think it needed adjustment
6 unplugged dme temp sensor and the car stalled so I'm assuming this is working fine and is only 6 months old
The engine runs exactly the Same with no difference what so ever.
Any ideas ?? Is it my tps I wonder ?

Well I finally sorted the problem and it turned out to be 2 things.
First I replaced my tps and this sorted the fluctuating idle problem but I still had the problem of high revs at idle,after close inspection it turned out I had an air leak on the throttle body itself at the bottom of the spindle where the tps goes,so have now replaced that and the engine runs like a dream , it's also cured the running rich problem that I had and the car is so much nicer to drive coming on and off the throttle,so now to get on with the rest of the list of jobs to do.
Cheers

Tel

Result!