Porsche Enthusiasts Club Forum

Hi everyone, I've just joined this forum and have started my Porsche ownership with a 91 928GT and I was wondering whether anyone can help with some advice on an issue I've been having.

From stone cold when I start the engine the idle can be erratic and often stalls when I return to idle soon after driving off. Moisture could be affecting the car, as overnight it's not stored in a garage and damp cold mornings or evenings do seem to make the stalling problem worse until warmed up.

Once warmed up, even after the car has been sitting for a couple of hours after the initial drive, it won't stall again that day and the idle speed is steady and around 800rpm. However, the next morning or afternoon it’s the same situation again. I have had a couple of non-stalling exceptions on warmish dry afternoons where the car hasn't stalled from stone cold.

A further note is that when I start it in the morning the idle can be erratic and hunts around bit, then if I rev it and let my foot off the revs drop to almost stalling but then recover and hunt again. Before it's fully warmed, and after its first stall, the revs can drop to 300rpm or lower then they increase without me touching the throttle up to about 1200rpm, then go back to a steady 800rpm.

After the stall the warning message is check oil level, which is fine as I topped it up just last week and 5 bar is the usual pressure...so I can't understand why that message shows.

I must say that this problem, (and even the fact that my air con isn't working), has not dulled my enjoyment of the car one bit..its just such an amazing car and the RMB makes it sound like a V8 should!

Welcome to the forum!

Can only speak from similar experience with VWs, however the very same issue on my Corrado VR6 was a combination of a stuck/sticking idle control valve ((ICV) - a cylindrical solenoid controlled device in the vicinity of the inlet manifold which opens at zero throttle to allow the right amount of air to bypass the throttle body) and a dicky coolant temperature sensor. On my car (Bosch Motronic electronics) the ECU, by design, assumed a default temperature value when the sensor packed up, and on cold mornings this particularly affected the fuelling, as the ECU was assuming a temperature significantly warmer than reality. The ICV can be cleaned with carb cleaner and a lint free cloth to remove any coking deposits that have built up, however check it's operation by applying 12v across the terminals, as it may have packed in altogether. Not sure if there is more than one ICV on a V8 monster?!

Could be leading you up the garden path here, but plenty of 928 experts lurking may have other suggestions... sometimes all it it takes is one reply wide of the mark for the floodgates to open!!

Cheers,
George

Welcome to 928 ownership!

I think you posted this problem on the 928.org.uk list so I may be duplicating advice.

Could be an Idle Stabiliser Valve but you can't physically clean it without removing manifold and unbolting the throttle body! The trick of squirting cleaner down the hose from the brake venturi y-piece has been known to work but is hit and miss.

Your best bet is to get hold of John Speake's JDS Spanner (Google for John's site) which will actuate and read error codes on a number of systems which could cause your idle problem including the ISV. It pays for itself very quickly in saving you time troubleshooting and avoiding replacing otherwise good parts.

It will also check the cold start sensor (the Temp II sensor, though you can also check this with a multimeter) which is another candidate for the problem.

So I recommend you buy the Spanner which will be a boon throughout 928 ownership and give you a head start in tracking down this problem to start with.

Keep us posted!

hi adrian, didn't get to speak on saturday, hows the intake job coming along ?

Finished last week Lindsay and together with the new injectors it feels fantastic! Was good before but transformed now.

I've noticed that if I give the car time to warm up, at lest a minute or so before setting off I have no problem with stalling...guess the old girl just needs to wake up before setting off!

It would be worth checking dizzy/leads/plugs too as that may be the cause of the hunting i.e. sounds like more than one issue here.

excellent news, will you be at weston park ?

I thought the problem had cured itself because if I let the car warm up in the morning for a minute or so it runs fine for the rest of the day. But sods law said otherwise and yesterday I tried to start it, it ran for about 20 - 30 seconds and died, after repeating the process three times I gave up and drove to work in other car!

I tried it again today and the same thing happened!! The oil pressure and level are fine, there are no warning messages, it has enough battery power and it starts right away, but just never lasts long...any ideas?

I'm beginning to wonder whether a novice like me should own a car like this! What am I looking for if I check the dizzy or leads...some moisture on them?

I'm thinking of getting the AA to take it to a specialist for a repair as I really want to drive it again. Would anyone be able to help or suggest someone who could...I'm desperate for a professional here!

It sounds like you really need a specialist to look at it but don't fret, it doesn't sound serious.

Does it idle ok when hot? If so then ignore above advice re: the dizzy etc and concentrate on the cold-start side of things. There will likely be a valve which is open at cold idle to get more air flow into the engine and this may be sticking. The other possibility could be the air flow meter sending an out of range voltage which is causing the ECU to shutoff the engine.
I would take it to an independent specialist if you don't feel confident having a go. Especially as I could be giving you a bum steer (I don't know 928s very well).
Perhaps someone could chime in with your nearest specialist as I'm afraid I don't know where 'Thames Ditton' is.

Thames Ditton is in Surrey, about half an hour from Guildford.

I'm thinking, after doing a bit of searching on the web and asking John Speake, that it might actually be the fuel pump relay, as it dies soon after starting, but again I don't know enough to test this!

I know how you feel. Been there with a '44. Stick with it. Probably somthing simple! Best way to check the fuel pump relay is just to swap it for a known good one. They just plug in. Had loads of trouble myself with no oil pressure. Turned out some muppet had fitted the wrong pressure relief valve for the car. Took Months to find that! Sure yours won't be so bad. (& I didn't have another car to use )

You should definately talk with John Speake. He is very knowledgeable and a real nice chap that I would recommend to anyone with a 928. His website is http://www.jdsporsche.com

As you're new to 928 ownership I would also recommend you add this website to your favourites:
http://www.nichols.nu/tips.htm Lots of help IMO

Thanks for all your help! John Speake told me I should try swapping the fuel pump relay with another one of the same, say for the horn.

With all this bad weather I haven't got around to it yet, but with relays do I need a special tool to remove them?

They just lift out, the relays are known to fail and a lot of us front engined guys carry a spare in the glove box.