86 with rough idle

[356six]

My car has a rough idle or more like a vibration (900rpm) which will smooth out if you bring the rpm's to 1100 or so. Once I'm driving it seems fine. Motor mounts check out OK. Any thoughts?

[nize]

are all of the cylinders firing properly at idle? i've seen this problem occur when there's a bad injector.

you can test this and locate the bad one by disconnecting one of the injectors at idle to see if it changes.

[356six]

I'll give it a shot - but wouldn't I aslo have poor performance under load?

[nize]

not necessarily, because if one of the injectors is over-flowing, the resulting mixture would be too rich to fire at low rpm's but may be lean enough to fire at higher rpm's.

i've had a similar problem and discovered that the pintle (needle) on one of the injectors had broken off, resulting in a 50% overflow condition in one cylinder.

[356six]

Thanks, it sounds like a good starting point as it does smooth out around 1100rpm & seems to have normal acceleration.

[Lawrence Coppari]

Mine has had a rough idle three times on me.

First time: Incorrectly adjusted TPS after I had throttle body enlarged and I reassembled.

Second time: Bad distributor cap and/or rotor. This did not show up above idle speed.

Third time: Bad idle stablizer valve. Symptom occurred when first started and cold. It was fine when warm.

Vibration at idle: Bad engine mount. Vibration goes away above idle.

[356six]

Turns out it was a bad motor mount. One side was crushed or flattened. Should be smooth sailing now.