Rough Idle = Vacuum Leak
I notice that my '90 GT idles a little rough, and also shows some roughness when slowly accelerating the engine up to about 2000 rpm with no load, trans in neutral. It's ok in gear and driving. It isn't missing on any one cylinder. If it had a carb, I'd try richening the idle jets a little to correct it. Is this a characteristic of a GT due to different cams? Maybe it has a vacuum leak somewhere? I can't hear a hissing vacuum leak though. The S & S4 has very smooth idle and stays smooth on up.
Vacuum gets my vote. I had a bumpy idle for over a year. Found a vacuum elbow that was swollen and loose last weekend. It took almost a week for the computer to re-program itself, but the idle is smooth as glass for the past two days. Hope it stays that way.
After running the car I'd disconnect the vacuum at the four way near the brake booster. You should hear a loud his when you disconnect it. If not its either the black and blue check valve or a vacuum loss somewhere else.
Kevin Berez (email@example.com)
'86.5 928S Auto Meteormetallic
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