big load

She will not hold idle.
On cold start up i have to turn and hold the key a few second before she starts up. Then when she does i have to keep giving her gas to hold idle otherwise she cuts out after a few seconds. I can also smell petrol from the exhaust. The only way she will stay running is if i hold the gas peddle down. Does anyone have an idea where to start looking for this fix????????????????

The Forgotten On

To help clarify what your problem could be. Could you tell us what year your 928 is?

big load

sorry i need to update my user cp.
its a 928 s4 5.0, 1989 on G reg

Tails

I would suggest that you do a "search" in the archives and see what it bring up. There are numerous procedures in a logistical order to try and solve your problem.

Remember the "search" function is your best friend.

Hilton

G-reg 1990 will have cats and an O2 sensor in the UK. G-reg '89 won't.
The first suspect is the Mass AirFlow sensor under the airbox. If you unplug it, does the car run the same, worse, or better? From the petrol smell, it sounds like its in limp-home mode and your MAF signal isn't being received by the ECU.

This can be due to:

Ancient MAF being out of range (they last around 10 years)
Damaged wires inside the MAF connector rubber boot
Failing/failed LH Brain
Random other wiring issues

big load

hi Hilton and Tails
thanks for the advise. Hilton if i have damaged wires inside the MAF connector rubber boot is this part inside the MAF? so changing it COULD half solve it. I'm taking it that it has not been changed for 10 years as the car has been sitting around since 2003.
Is there a test or check I can do on the "failing/failed LH brain?

finally anyone have a link for the engine bay list of parts IE diagram for where everything is?

big load

Tails i tried the search but did not find any thing relevant. also can someone tell me how to add the details of my car into a signature type thing...I cannot find it in the settings anywhere

Mike Frye

Big,

The signature is part of the 'user cp' menu. It may be that you can only do that if you're a member though, I don't know.

Best bet if you can't find anything about adding a signature under user CP (control panel) is to just include the info in the title or manually at the end of the first post.

I can't believe you couldn't find anything useful about a rough idle by doing a search. It's probably the most common topic on here after tire/wheel questions and which oil to use. I would suggest looking under 'rough idle', 'Idle problem', and maybe 'idling'.

You should find lots. The manual has an entire section on troubleshooting the engine with a step-by-step set of instructions to work through to ensure everything is as it should be. This includes cleaning/checking connections and ground points, vacuum and pressure tests to perform, and some points where you can check the switches, wiring and sensors to confirm they're all working right at both ends and all along the path.

Mrmerlin

you may have to be a member to access the user ID section,
18.00 US will get you there.
Then under user CP at the top click on it ,
then click edit signature.
For your car if it was running fine then all of a sudden you have this issue,
I would say your LH has failed,
remove the LH computer from your car,
and install it into another good running car to test it

newworld

87s4. Same issues here. Exact same.

For cold start, new sensor temp...measured ohms and in correct range. Did it help cold start? No. Checked wiring on boot and replaced but still no cold start but starts up fine afterwards.

Idle on startup 500.600. If I throttle it will stall. Changed out maf and lh. Same thing.

Will startup fine when warm.....

I have new isv new tps did intake refresh.


Bottomline is I read all posts...there are so many variables that no one really knows the answer.

For some changing temp sensor helps cold start. I need to squirt carb cleaner in intake to do a cold start.

Once car is warmed up.....sometimes after throttle it catches itself and saves it from stalling....but it let's the rpm drop pretty low enough to get some dash board lights to light up for a second

John Speake

If you send me your LH ECU "Jetronic" and your MAF, I'll test them for you.

It might save you a lot of time and needless expense of throwing parts at the car without a clear reason for thinking they are faulty... email me from the link on the website in my signature.

89FrontPorsche

big,

Here's where I am so far. You might just check if your fuel pump(s) is/are operating. If you have the in-tank pump, it may have failed, causing the external pump to get hot and fail. As has been said here numerous times, the external pump doesn't like to suck; It likes to have fuel fed to it.

I have opted to remove the failed in-tank pump and replace it with the strainer, currently awaiting parts. However, some have suggested that the in-tank pump was installed for a reason and although I agree, there are others who have said that it can be omitted without issue, unless the car is in high temp areas or high altitudes or both. I plan on seeing how it works without the in-tank pump first though I have considered just purchasing a new replacement in the event the single pump arrangement doesn't work.

My symptoms were similar to yours though I could hear the external pump whining loudly. My guess is that since it had not gotten hot, it was close to failure, which is unusual for a 928 external fuel pump. However, I had thought the pump had been changed, based on writing on the filter which was dated for 2011....yet I double-checked and found no writing on the pump and therefore must assume it's original.

However, However....the pump is painted, telling me it's the high-output pump. The stock pump looks identical in shape and construction, but is unpainted, so I'm led to believe. In any case, it's a guess.

Bottom line, after all that verbal vomit, you could have a bad MAF...a bad LH...a bad fuel pump (or two) or...simply...the fuse and/or relay to the fuel pump may not be allowing the pump(s) to operate. Fuse is #42 on US cars. Fuel pump relay is #XX (top row, fourth from right). As was told to me, if it has a metal body, change it. #53's are pretty inexpensive.

Check the fuse for dirty contacts...but clean the blades anyway.

I have changed my MAF as maintenance on my car was unknown and the MAF would go bad sooner or later. The LH computer is probably suspect as well but that's big money and requires an exchange.

Additionally, the hard fuel line between my external pump and filter had been kinked in two spots. That can't help fuel delivery at all...though it's odd to consider that a factor since I've driven the car trouble-free for ~ 6 months before the idle, cutting-out/dying thing started.

You may have your work cut out for you. Even an experienced 928 expert will be challenged but approach the things you can do yourself first, then if necessary, get help.

Hilton

The failure of the in-tank fuel pump will cause issues with running poorly, but won't create a petrol smell at the exhaust as it runs lean. Often an in-tank pump failure won't even be noticed as the small hose on it splits letting fuel flow freely around the pump itself. In my 89 when the pump failed and the hose wasn't split (5 years or so after I repaired the in-tank pump's connecting hose), it would still run and idle ok, it was only above about 3k rpm's that it struggled.

"Big Load"s description sounds like its running way too rich, which implies MAF issues. Sending the MAF and LH to John Speake is a good idea for testing (he's in Cambridge).

The rubber boot I mentioned is on the harness side of the MAF connector - its the small rubber boot that protects the wires as they go into the 6-pin plastic connector. The insulation on the wires in there commonly cracks due to flexing from unplugging/replugging the connector, as they're heat/age hardened. Once they short, they can cause all kinds of troubleshooting headaches. On my most recent S4 I preemptively cut the boot off to check them and then used some self-amalgamating silicone tape to make a new boot once they were verified ok.

Another easy thing to check is that the vacuum ports on the fuel pressure regulator and dampeners aren't leaking fuel (especially the fuel pressure reg). Check the elbows for petrol smell with the engine off.

My money's on the MAF still tho'.

big load

hi thanks for every ones reply and help so far. i'm trying to digest this
OK the car is going for a cam belt and pump change at the end of this week. once it comes back i'll contact you (John Speake) and see what can be done.
out of curiosity the LH brain is that expensive? does it need reprogram after fitting? or as john has suggested it can be checked and possible repaired. any links to where this item is on the car....and don't say left side :-) hahaha

also can anyone tell me what is a good price to pay for a timing/cam belt change and water pump. i'm being charged 871 plus VAT. also anyone know of a a good cheap place to buy parts for these 928.

stuartph

Big

Your best off buying from roger 928rus in the US

In the uk eurocarparts and gsf to bits and bobs