Tickover problem - any ideas?

[rjc]

My 964's been running fine for the 3 weeks that I've had it but has now developed a tickover problem i.e. it won't, it just stops every time I come to a junction/lights etc. It starts up from cold fine (without touching the throttle) but once its warm it won't tickover. Starting from hot is OK as long as you press the throttle as it fires. Apart from the lack of tickover problem it seems to be fine, no misfires, roughspots etc, accelerates as smooth as a nut. I thought I'd found the problem the other day when I noticed that one of the thin vaccum tubes near the throttle linkage had come adrift, but even after replacing this, it still has the problem. Sometimes it's fine, but most times it either won't tickover at all or it hunts a bit and then stops. Any suggestions? Where do I start?

 

[peanut]

I'm not familiar with the model I'm afraid but assume it must have a throttle idle switch thats where I would look first to make sure it is set correctly so that the switch is working properly when the throttle position is at rest otherwise the favourite culpret is likely to be a leak on the inlet side, on a hose or joint somewhere.
If its possible you could try partially blocking or restricting the air intake and see if that cures the tickover. That would confirm a leak somewhere

 

[Dave Wilkinson]

Robin,

It sounds as though you have a problem with a sticky ISV (Idle Stabilisation Valve). The valve is operated by the DME to stabilise the idle speed and it's a common problem, particularly if the oil has been overfilled at any timne in the past.

The valve sits right on top of the intake - dead centre at the top. You need to remove it and clean it internally with some carb cleaner. DO NOT attempt to operate it manually as it is easily damaged. Click here to a page which describes the same process for a 993. It's very similar although not identical.

Regards

Dave

 

[rjc]

Thanks for the suggestions guys. I shall investigate and report back...

 

[rjc]

So I finally got round to removing the ISV and giving it a thoroughly good clean with brake dust remover. When I removed it I could see some evidence of engine oil in the ISV and the breather pipe that feeds it, so I was optimistic that the clean up would cure the problem. But alas not. The first time I started it after replacing the ISV it ticked over very roughly and with a good deal of hunting. Then I switched off and a minute later started again and then it seemed to run perfectly, ticking over smoothly at about 900 rpm. I took it for a run and it ticked over perfectly the whole time. Then I switcehd off and started up again a minute later and it was back to the rough tick-over/hunting/engine stopping. Having got it sort of ticking over, I tried unplugging the ISV and the engine immediately stopped so it's obviously doing something. I've checked all the wiring very carefully and everything seems in order. The fact that it runs perfectly on some occasions and not others does seem to suggest an intermittent electrical solenoid somehwere. Apart from the idle problem the engine runs perfectly, no rough running or anything to suggest another problem. Any suggestions of where else to look ?

Thanks,

Robin

 

[Big_nige]

cleaning the valve will only do so much, I'd try a new ISV before doing much else.

 

[smallspeed]

check the throttle return springs are all ok, and the operation and setting of the switch underneath the linkage.. if this switch isn't getting "switched" then the car will not revert to idle condition and might stall.. I had an old merc which did exactly that, and was cured with a 25p return spring..
Ill keep my fingers crossed for you []

 

[Elliot Davies]

See my posting with a pic as this helped mine
http://www.porscheclubgbforum.com/tm.asp?m=82481&mpage=1&key=idle&#82521

 

[Steve Brookes]

If Elliot's tip doesn't solve it. Have you checked if the thin vacuum line you found adrift at the front (attached to the Y piece) is properly attached to the back of the air box? Also try checking the hose clamps on the inlet manifold. A leak on these can cause tickover problems.

 

[skendrick]

I had a similar problem on start up when cold, went around the engine tightening up all the hoses and it was fine after.
Didn't cost anything either.

 

[Paul 944 s2]

My 964 has a similar problem a local Porsche specialist plugged it into his Bosch hammer and it said it was a faulty throttle position switch - these are about £130 for 2 small micro switches