95 964, 154,400 miles.

The car has developed an intermittant rough idle when the engine is hot.

Observations :

On cold starts the engine doesn't run up to 1,500 rpm immediately, then down to ~800 rpms now. It starts just fine but it starts and stays at ~800 rpm right from the start.

The rough idle is only noticeable in Neutral and when the engine is hot.

Engine vacuum is very good throughout the engine temp range.

The engine idles smoothly in gear.

It doesn't always idle rough in neutral when hot, but most of the time it does. It will idle smoothly then you can feel it shake once in a while then it will just shake constantly, throw it into gear and it smooths out.

There is an intermittent cylinder miss when you listen to the exhaust only when the engine is hot. It is not a regular miss and is defintely intermitent. Sometimes worse than others.

What I have done:

Checked for vacuum leaks, none found.

Cleaned the flame trap, IAC valve and the throttle body.

Ran injector cleaner thru the fuel system and changed spark plugs (this did seem to made the rought idle a little less severe and slightly less frequent), I've checked this over several days so it's not my imagination. So a slight improvement but since I did both at the same time, I don't know which had more of an effect.

Any thoughts are appreciated.

DEWFPO



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1998 S90 071,245 and 1995 964 154,100