928 S4 running very lean and rough
 

Good morning to all from KwaZulu, South Africa. I have a 1988 Porsche 928 s4 which I have substantially refurbished.
She was running beautifully until just before Xmas. One morning ,after starting,was running very rough and lean. Fumes burn your eyes!
Also, she's not enjoyable to drive at all. Nothing happens when accelerating and then suddenly catches and surges forward!
Alarming in a built up driveway!
Local mechanic sprayed aerosol in the vicinity of the fuel rail and inlet manifold on the drivers side of the engine. Seemed to improve the idling temporarily.
He says he thinks it's worn injector seals or inlet manifold seal.
Is that like likely?
Also another mechanic ,who worked on the car,says he thinks it could be a cracked or loose vacuum pipe or pipes.
Only way to drive her to repair is to pulse the accelerator to move her forward in short distances. Not too bad once we're on the highway. Worried I may be doing damage.
Any advice please?


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My 86 will sometimes be hard starting and run rich. I put a bottle of Techron in the tank which usually clears it up. Look at those dampers and regulators on the fuel system for leaks. How are the rubber fuel lines? Maybe bad pressure valve on the fuel pump. Check for vacuum leaks.

for your car the two most probable things that will cause this are the MAF going out of correctable spec,
and the LH computer failing ,
SO I would send the computer off for rebuild ,and do the same for the MAF .

Inspect the ignition coil wires ,
make sure they are not rubbing on any part of their run ,
and the ends are not corroded.


Clean all the connections at the battery and replace the ground strap

^ What Stan says.
Service your grounds and other electricals anyway.
It is likely your MAS or LH.
See this link for John Speake for the rebuild.
Porsche 928 Fault Diagnosis - JDSPorsche

+2 on the above responses.

Does your engine idle high? Check all vacuum lines carefully.

Was thinking of one more thing for you to consider.
You say runs very rough and lean - 'fumes burn your eyes !'
You say the car kind of stutters until you get on highway and than runs well. Higher rpms can can mask a single non firing cylinder.
Not good if this is unburnt fuel coursing out through the exhaust. Risk of ignition in a hot catalytic converted if you have incomplete firing/ignition of spark plug(s).
You can do a simple test of the 'spark' at home without have to drive it to your mechanic and risk having unburnt fuel in the exhaust system. See the attached link for the how to and purchase an inexpensive little tester to do it.
Things that can cause lack of spark to a single cylinder are a bad spark plug, a bad ignition cable, a degraded ignition rotor. I doubt it is a bad ignition coil cable for you would have 4 cylinders down and would run terribly even on the highway, which you said it didn't. Exclude this as a cause before you drive it to your mechanic. If this test is good and you have spark on all cylinders then look to MAS or LH computer.

https://www.youtube.com/watch?v=9Vl9JlIFiic

Huge thanks to Harborman, Mrmerlin, Stepson and MainePorsche! For all your advice on my 1988 928 S4 running so uncomfortable rough and lean.
Investigated as you suggested.
A few weeks ago I had cosmetics done on the engine and I discovered that one of the fuel rails not fastened properly. It had worked loose and was causing all my problems.
So nothing more serious than that!
Have fastened it and it's now running great.
Africa is a lonely place to own a 928. Very little advice or knowledge around. Parts and service.
Even local agents and distributors not really interested or knowledgeable about the 928. Mostly want to talk about the later and more profitable models.
So we have to rely on websites and you guys.
So thanks again for all your concern.

You are welcome here any time. Thanks for letting us know how the problem was solved.