Will worn guides cause misfires at idle?
 

I have a 96 993 with 75,000 miles. I suspect the valve guides are shot. Oil consumption is about 850 miles/litre, close to threshold. I know the 993's are bad for guides.

The idle of the car is pretty rough and you can hear the occasional **phut** **phut** soft misfire in the exhaust mostly on the right hand side. The engine seems to pull strong otherwise.

Has anyone seen a rough idle like this linked to worn guides? The theory that was put to me was the valves are so worn that they do not seat well and thus a rough idle. I will search for other reasons for the bad idle as well. I have talked to Wayne and he has seen it happen on other cars but I thought I would ask the list to see if its common.

The ignition system has been checked with new rotors/caps and spark plug wires. Plugs are almost new. It idled rough before these parts were replaced and still does. The engine is showing high hydrocarbons on the exhaust. The vacuum is strong but I have not searched for small vacuum leaks that can affect these kind of cars. I get CEL's indicating misfires at random cylinders.

Pehaps its time to ante up and do a top end rebuild but I would like to explore other causes first.

Cheers,

Mike

it would be a lot ezer to check the guides then to check the theory

Well, I know a 993 with 75,000 miles will have bad guides.....that is almost certain. However I also have a rough idle, is that a result of the guides or something else? While I am chasing the something else I thought I would ask if anyone has seen a direct correlation between valve guide wear and the rough idle/misfires.

Cheers,

Mike

Did you get my email?


Jeff

Yes I have Jeff and thanks! I sent you a reply.

Cheers,

Mike