Porsche Enthusiasts Club Forum

My car seems to be suffering a little from poor/low idle sometimes. I have read that spraying WD40 into the hose to the ICV may possibly fix a sticking ICV. The picture comes from a left hand drive so the layout appears a little different (i.e brake booster is on the other side) but apart from that it seems the same. I have stuck an arrow on the picture, can anyone tell me if I have got the right hose?

i had an erratic idle so i took the icv of and gave it a thorough clean with carb cleaner, cured the problem and its still fine.

Do you know if that is the right hose? The idea is that you can just fire a good blast of WD40 done the hose and free it that way avoiding having to remove the icv.

I am not sure the ICV is my problem but as the above method is quick and easy I thought I would give it a go. It could be coincidence but I think I have a problem with the HVAC system which I believe can cause running issues. Every now and then there is quite a loud tapping noise that comes from behind the dash. If I switch the fan off and on it usually goes away hence why I think it is HVAC. I’ve seen a write up for checking for vacuum leeks so I will give it a go when I get some time.

Hi Mike

Yes that's the correct hose (LHD or RHD not different in that respect).

The WD40 trick more likely to work if you block off one outlet of the connector at side of throttle body where the hose terminates. For details post on 928.org.uk list where this came up last week.

You are correct that HVAC system uses engine vacuum, but it draws vacuum via brake servo via check valve, so leaks in HVAC do not effect normal running (apart from flappy valve not opening at high rpm).

Have you checked whether idle switch section of throttle position switch operates correctly?

Cheers

Adrian

Thanks I'll check out 928.org.uk. I've been meaning to sign up there


Ok so this is unlikely to be the cause of the problem. I read from here http://members.rennlist.com/pirtle/svc_act.html that vacuum leeks can cause various problems including idle. As I can hear an issue in there it seemed like a good place to start. I have the pressure checking tool coming so will check it out anyway as I will want to fix the noise. Not so sure I want to pull the center console apart but I guess I could stick in a new stereo while I’m there.



Nope I'll look into that. If you have a link to the procedure it would be handy.


I will say that my idle issue is intermittent. Not 100% sure but it seems to be only after a warm start, I haven't noticed it when driving from a cold start. The car will sometimes stall at the lights or when maneuvering. Some other posts I have read point to the ECU or the MAF. The previous owner put a new ECU in recently so it could have perhaps not been done right. I read that the MAFs need recalibrated every now and again. I wonder if this is a possibility?

John Pirtle's site (fab resource for 928s) is correct - vac leaks cause idle problems. But he means leaks around inlet manifold. You may well have hvac vac leaks, but they wont affect idle or running aside from flappy valve not opening at high rpm.

To check idle switch move the throttle quadrant (next to hose you plan to squirt down - with all cables attached) very slightly off stop. Do you hear a click?

Your hot/cold symptoms suggest possible fault in temp II sensor. As you face engine bay it is on left of coolant bridge with 2 spade terminals attached. Take off terminals and if you have meter measure resistance between each of the 2 terminals and an earth (not between terminals). What are readings with cold engine? What about hot?