Idle problem - help required

[andrew_churcher]

Hi All,

I just want to see if I can get some assistance on a problem I am having with my S2.

Basically, after I have driven the car for approximately 15-30 mins.......stop the car......come back to it 20 minutes later and go to start it again......the car starts....but idles around 200 rpm.....not up near 900 rpm where it should. It runs like that for a few seconds and either stalls, or after 5 or so seconds perks up to the normal idle (not all the time though). Usually I turn it off and on again and that sorts it out.

The car starts and idles fine from cold, starts and idles fine after I have driven it for 15-30 mins.....turn it off then immediately start it again (checked that today)........it seems to be when its left for a while to cool down then go back to start it that this issue appears to rear its head.

I took it to a specialist for diagnosis and cure last week (amongst other things). Based on the history file with the car, the idle control valve was actioned less than 6mths ago (10/6/09 - less than 4k miles ago) the previous owner probably had a similar isssue. The details from the service invoice are below.

" Collect and deliver car. Check for idle fault, check over basic engine tune, check breather system and air hoses (ok). Strip out remove idle control valve, clean, test and refit. Strip out and remove throttle body, clean housing and throttle butterfly, reset butterfly and refit throttle housing with new allen screws. Check and adjust throttle switch, check CO%.

Upon hooking up the diagnostic equipment and doing some more analysis (after they originally diagnised no problem...which based on the above...i can see how that could happen as the test drive needs to be lengthy and it needs to sit for a while before restarting to replicate the issue) it was decided that the oxygen sensor was giving inconsistent readings and this may be the culprit...so I gave the approval for that to be replaced.

The idle problem described above happened twice today. Turning the car off and then on again seemed to fix the problem and off we went. I just cant understand why it doesnt start properly the first time and idle correctly. Its quite irritating.

I plan to keep the car for a while so I want to rectify issues like this. Its the first chance I have had with the car back to test the work done and so far....doesnt seem to be any better than when I took it in.

On a brighter note - upon returning home i ran into a guy who rents a space in my complex to store his 89 911 carerra. It was a nice machine.....but in seeing the old 944 he was suitably mesmorised that he opened his car door and the 2 bottles of red wine he had just purchase fell out and smashed all over the ground. The effect of a guards red 944 hey!!!

Rgds,

 

[AndrewS]

Hi Andrew,

The idle on a 944S2 is managed ultimately by the ECU which receives a number of sensory input signals. The ECU controls the idle using the ISV (Idle Stablisation Valve).

You could try swapping out the ECU with a known good unit and testing the car. I would also suggest a vacuum and pressure test to ensure there are no vacuum leaks. It is also worth testing the AFM (and connections) to make sure it is generating the correct readings. Again, swapping out this part can help the process of elimination.

Best advice I can give is to take it to a suitable specialist that knows how to diagnonse these cars properly. There is a specific diagnostic process to follow with a multimeter to accurately diagnose this kind of fault. A suitably experienced and equipped specialist will be able to accurately diagnose the root cause. You will then only spend money on the actual resolution (with the certainty that the problem is fixed once and for good).

Regards,
Andrew

 

[andrew_churcher]

thanks for the response Andrew.

 

[delasalle]

Check the fuel rail pressure - you could be getting vapourisation of the fuel in the rail because the pressure is not holding - due to either leaky injector(s) or below par pressure regulator. Steve

 

[dac68]

Hi Andrew,
I was experiencing a similar problem a few weeks ago and one of the suggestions was to a) either take the idle stabilisation vale out and clean it or b) use some carb cleaner via the intake. I went for b) as I have little spare time to get the valve out. The problem was sorted for a couple of weeks but as of yesterday morning was back. I'll have to find the time now I guess. []
Hth

Regards,

Dave

 

[andrew_churcher]

Hi Dave - thnks for the note.

I think with mine as a) has been done recently it may be something else. Some more systematic checking at a specialist is required me thinks (as per Andrews advice)

I thought this site was very good though even if just for a bit of self education with these issues.

http://www.clarks-garage.com/

Under the garage shop manual link go to "Troubleshooting - Engine" and it runs through most common problems and what the cause may be.

Rgds,

 

[sulzeruk]

My money would be on the idle control valve as they only removed it and cleaned it. It is the only item that can alter the idle characteristics of the engine when the engine is hot and cold. Worth taking it out and cleaning it properly in an ultrasonic bath if you can get access to one. I have one here if that helps.
Alasdair Cowan

 

[zcacogp]

Andrew,

Can't help with an instant diagnosis, but if you wanted to pop 'round for a day of tinkering with swapping ECU's and whatnot then I'd be quite happy to help. My S2 is an '89, although I can't remember when yours was made. (Later ones had a different ECU I think, and I'm not sure if they are interchangable.)

I also have an ultrasonic bath if you wanted to clean your Idle Control Valve in it.


Oli.

 

[peanut]

ORIGINAL: delasalle

Check the fuel rail pressure - you could be getting vapourisation of the fuel in the rail because the pressure is not holding - due to either leaky injector(s) or below par pressure regulator. Steve

yep I'd go with this too. Other possible culprets are the non return valve in the pump and the fuel pressure damper letting the fuel pressure drop. Worth doing a fuel pressure leak test
Another possibility is a faulty inlet temperature sensor which controls the cold start valve. Cold start operating with a warm engine could flood the engine

 

[andrew_churcher]

thanks for all the tips and offers of help guys. I have booked it in to get looked at by a specialist in the coming weeks. I will let u know how I get on.

 

[zcacogp]

Andrew,

Out of interest, who? Tower Porsche, or somewhere else?


Oli.

 

[appletonn]

ORIGINAL: zcacogp

I also have an ultrasonic bath if you wanted to clean your Idle Control Valve in it.


Oli.

Oli finally reveals the secret of his youthful good looks and soft skin....[][][]