Rough idle on a 1992 960 with 271,000 miles. When engine is running above 1200 to 1500 rpm, the rough operation disappears and it seems to be running smoothly. But, once idle again at a stop light or something, the rough idle comes back and is usually bad enough to shake the whole car.

Just got done cleaning the throttle body today, and that didn't seem to fix anything. I put some fuel injector/intake valve cleaner into this gas fill-up but that hasn't seemed to do anything yet after about 40 miles. Spark plugs replaced within the last couple months. Oxygen sensor replaced within the last couple years. PCV flame trap replaced and other PCV components cleaned up just recently. Had a 2-3-2 trouble code, which was lean fuel operation, but cleared that and it hasn't reappeared yet. No other codes that I know of.

Just confused and trying to figure out what is making the idle so rough that it shakes the whole car and you can feel it while sitting in it.

I'm thinking I need to clean the fuel injectors more thoroughly which means taking them off and cleaning them myself - anyone have advice on that?

Thanks in advance.


ScottyD

Get the motor hot, then, without getting the MAF wet try dumping a half a gallon of water into the intake. that should shock alot of the carbon deposits off the inside of the motor. If nothing else that will help with fuel economy, power, etc...

Andrew

...try dumping a half a gallon of water into the intake.

AMS, I am sure you don't mean "dump". When trying to thermal shock carbon loose, use high RPM and work the throttle to keep the engine running while slowly introducing water to the intake. Too much water will hydraulic lock a piston; bad juju.

ScottyD, the symptoms you report sound to me like a vacuum leak. Hose off or split?
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Mr. Shannon DeWolfe -- I've taken to using mister because my name misleads folks on the WWW. I am a 52 year old fat man. ;-)

Try this and I think you'll find the problem--take a butane or propane torch
cut on the gas--don't light it up though--now with the engine at idle
point the tip of the torch around where the intake attaches to the head--if the idle smooths out you will have found you have a bad intake gasket. This has happened to many here in the past--the old red intake gasket has been replaced with a newer green part that won't give up the ghost as often.
Hope that helps.

Poolman's suggestion is more likely, also check the rubber intake after the MAF, are there any cracks, is the small idle hose tight on both ends to it's fittings?

Is the air duct (foil hose) still attached to the intake? The valve has stopped working and it may now be drawing heated air from the exhaust manifold into the air stream?

Are all vacuum hoses in place and secure?

DanR '94 964 342,000 miles (108,000 on the new engine)
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DanR

Thanks for the responses everyone...

Tried the propane gas around the intake manifold and other intake areas past the air flow sensor, but nothing changed - rough idle persisted throughout.

Don't really want to put water into the engine intentionally, so that may be a last resort fix.

I looked quickly at the vacuum hoses, but probably not as in depth as I should. I guess I assume that the problem is a clogged fuel injector since the propane didn't change anything. I'm going to dump some more STP complete fuel system cleaner into the tank when it's only half or quarter full so its more concentrated and we'll see if that works...

When my intake gasket was leaking, it passed the propane test, but decided it had to be the gasket, and it was the problem.
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DanR

Gotta agree Dan--as old as that gasket is--it should have failed long ago.
On the vacuum hose's--if you haven't already--replace each and everyone of them--where the hose's plug into the intake--there's a 10mm bolt holding the vac tree into the intake--remove the bolt and take out that vacuum tree (this is where all the hose's come together) There is an 0 ring there--I have tried replacing it before--decided to use sensor safe silicon and just glue it back in then replaced the bolt to tighten it back down. Let it sit up overnight
before cranking--you will tell a difference.