1997 C4S rough idle

[Criss Yelton]

I have a stock 993. It has had a rough idle which has been very difficult to diagnose. My mechanic found unburnt fuel in the exhaust from both banks of cylinders but no fault codes. Changing MF air sensor, plugs and checking intake gasket resulted in no change. Compression and leak down tests were found to be good by several mechanics. A bad injector was diagnosed and replaced with no improvement. My valve cover was leaking slightly ; while replacing this he inspected the valve lash adjustors (exhaust) and found them seized. They were replaced with great improvement in the rough idle ; mechanic says the gasses are now perfect and he thinks the occasional roughness is due to the clutch or flywheel possibly.

Has anyone else seen a problem with the valve lash adjustors ? Should I be concerned about the intake valve lash adjustors ?

P.S. A charcoal cannister was found saturated with fuel and was replaced.

[Gabriel]

Have you tried the ISV valve?

have a look here p-car.com/diy/isv/

[Criss Yelton]

The ISV was cleaned X 2 with no benefit.

CY