mtbryder

Just purchased a 1995 993 (70K miles on it). The PPI suggested that I do a 60K service, which was just done. Also, a set of lifters were replaced on one side. The noise from the malfunctioning lifters is gone, but now the car shakes noticeably more at idle, as compared to how the car was before the 60K service and replacement of the lifters. I spoke with the mechanic afterwards, and he too really didn't know. He suggested to run the car hard, use good gas, and hopefully things will settle out.

Any of you folks experience this symptom? I searched the threads, and saw a bunch of things on ISV's, plugs, etc. It would be hard to believe that something failed right after a service.

Would replacing the other set of lifters help?

Robin 993DX

A vaccum leak from a line the mechanic forgot to connect?

Turn the A/C on see if the idle smooths out?

mtbryder

Robin,
Turning on the A/C does not smooth it out. Would you happen to have a picture of those vacuum lines I should look for to see if they are connected? Everything is new to me. Thanks.

Robin 993DX

I assume during the 60k service they changed the plugs, so in that case they would have to remove the heater ducts on the left side of the engine, which would result in removing 1 or two vaccum lines. Check for any loose vaccum lines hanging around that area. Since the car was running fine prior I assume there are no other issues that should cause the idle roughness.

4sound

Is it getting a "Pop" type sound in mufflers at Idle ?
I have never seen this done, but there are different size lifters sold by Porsche. For example, if the heads were cut a specified amount that required the lifter to have more length, you would order the lifters from Porsche accordingly. Once again, I have never seen this problem, rather, I am throwing out an idea.
One thing I see over looked are spark plug wires sets and spark plug end connectors. I saw a 993 once with a rough idle, yet no codes would show up. When checking the plug wires, they checked out to be ok. However, replacing the spark plug wire set gave it a great idle. The problem is replacing the spark plug wires with the engine in the car. It is a pain. To do it correctly, the intake manifold should be raised. Of course it is much easier if the engine is out. ( Also, a 993 spark plug wire set is not cheap.)
If you think you have a cyl that might weak, or having a major miss, here is a primative way of checking. You need to be able to see under the engine with a clear view. Get the engine hot and allow to idle. Get a spray bottle and fill with water. You can spray the water on each exz. manifold and check to see if it burns away quickly. If one cyl shows not to, you have found the weak cyl. DO NOT spray carb cleaner or brake spray. Spray small amounts of water. If there is a spark plug wire with a cut in it, by doing this primative test of spraying small amounts of water on the spark plug wires may show up a problem if there is any damage like a cut in the spark plug wire. If there is a break internally in the spark plug wire, this primative test will not show if there is a problem.
Of course all the suggestions Robin 993DX and others have made should be considered.
Good luck and let us know what it turns out to be.