Flint

I replaced my spark plug wires today, and unfortunately it did not eliminate the rough running at idle. It did, however, give back some low-end power I seemed to be missing after the TB/WP job and generally make the car smoother under power. But, when I sit at red lights with my foot on the brake, the car starts to shake like it is trying to break loose from some kind of restraint.

So, in the last couple years I have replaced spark plugs, distributors, coils, wires,, RR'd the intake, cleaned up the MAF, and removed the air pump and went through the vacuum lines (though there may still be leaks/blocks in one or two spots I took note of).

Any suggestions what to look for next? I have not really messed with idle settings or air/fuel mixture (though I have a RRFPR and AFM not yet installed, kinda waiting to get it running well first).

MarkRobinson

spec the temperature sensors, ensure your timing looks appropriate via timing light, ensure you have 30psi @ idle fuel pressure. you might have a dripping injector (did'nt' I just type this on another thread??). Also, swap your Mass-air sensor with a known good one to rule that out...also, inspect the 6 wires into the Mass-air: ensure the sheathing is not broken & the bare wires are touching.

Mark

Flint

Hmmm, I think I'm going to have to install my AFM before going further. I forgot to mention that I also had the injectors cleaned., which obviously wasn't the problem.

Bill51sdr

Sounds like this happened after the TB/WP job... you sure the timing marks are all lined up?

Flint

Unfortunately, it's despite the TB/WP job, it was basically as rough beforehand (a little better now). I'm taking baby steps toward optimum, it seems.

Normy

I have an '85 S2 [Euro]. You've checked your MAF then; did it run better for a while after this...then slowly started to run rougher and rougher...?

I did all the things you've noted above, and then last year on a whim I cleaned the MAF connector- suddenly the car ran far better. I used dielectric grease to attempt to seal the thing, but it is acting up again so I guess I've got to take it apart and do it over.

Try that before you do anything- use Deoxit cleaner and dielectric grease on all your connections.

N

Flint

Good idea. I did not do an extensive cleaning of my MAF (besides just wiping all the dust off and replacing the mesh on both ends. The car as a whole has gotten progressively rougher over the last couple years I owned it. I figure its just at that age. My only immediate goal is to get it back to a daily driver (so I can get rid of my actually more expensive second car), then I can slow down and begin more gradual reto work.

tv

No matter the age it should run smooth, strong, and hard until you have to replace valve guides or piston rings. I have an 85 euro as well. I was going to say to check the twin dist. and the cams for timing. Next i would say that a rough idle would be what i had right after i pulled my engine and replaced it. I had forgot to snug a few things down and a LOT of free air was getting into the intake.

After realizing that and tightening everything up, smooth again. Also read the test plan for 85 booklet on morehouse #2 cd plus WSM. for problem diagnosis. But not mush is smoother than a euro.

John Struthers

I might be TOTALLY IGNORANT here but I thought you could do a MAF check by starting then
disconnecting the harness connection.
If no difference MAF is bad?

jyoon

i had a shake at idle and a rebuilt maf fixed it. check jdsporsche.com for symptoms.

Dennis Wilson

Flint,

Have you tried it in gear without your foot on the brake? Try it with just the parking brake then if the idle smooths out, check for a leak in the brake booster, check valve or vacuum line in between.

Dennis

Flint

Hmmm, some interesting ideas, and stuff to try but I'm going to throw one more thing in the mix that I just now remembered:

My mechanic maintains that at some point a PO installed aftermarket "high performance" camshafts (as opposed to the Euro-S ones, I guess), and I now recall that he said that will cause rough running at idle. And yes, it certainly does sound like an American V8 that someone has souped up, has anyone else had that experience with hotter camshafts on these engines?

Dennis Wilson

The rough running (AKA loping) American V-8's was normally not due to the cam lift or duration but rather the advanced cam and ignition timing. If your HP cam was not machined properly, it could have flat spots which would cause the rough idle.

Dennis

Flint

Which would obviously make it harder for me to diagnose "normal" rough running causes. I have not personally confirmed this, so I will continue to work on the usual problems regardless.

John Speake

Hi Devin,
How many miles on your 928 ?

A MAF disconnect is only useful for diagnosing gross MAF failure - yours may be just badly aged.

Regards