I just bought a 2005 CTT this weekend. Love it so far, except for the rough idle.

The previous owner swears that he replaced all 8 coils and spark plugs just a few weeks ago. I had a PPI done by a Porsche dealer and they found misfires in Cylinder #2 and #4, but there are no codes.

What do you guys think?

Should I go ahead and replace the coils and plugs again in cylinder #2 and #4 (the previous owner swears this was just done)? Anything else that would cause the rough idle?

Thanks in advance.

 

Air leak.

If you get un-metered air or vacuum leak it can cause misfires.

I would check all the connections around the "Secondary Air Injection" pumps at the back of the motor. (big canister looking things over each valve cover).

I would also check all the rubber hoses at the front of the motor by the throttle body. There are several up there and if any got moved around they can get small tears and leak.

Lastly, you could check down by the by pass valves, and the valves themselves. They do eventually wear out.

Hope that helps.

 

Thanks, Cole.

Unfortunately, I'm very experienced when it comes to hunting for air leaks, coming from a highly modified Audi UrS6.

Do you guys ever test for leaks by blocking off one end and shooting air into the system?

 

I know what you mean. I had a highly modified B5 S4. I don't think there is any way to pressure test the intake and vacuum system. I know we used to pressure test the boost system on teh B5 but I think part of the leak on a CTT might be outside that loop.

Side veiw pic of my B5 S4 motor. (we got carried away)