If it is missing only at an idle, to me it sounds electrical. What I ment by the scanner is this. There are scanners that can be used when the engine is running and the vehicle is being driven. That way when the engine miss occurs, it can capture what is happening and from that, the mechanic should be able to pinpoint where it comes from.
As far as a valve spring. You would hear that all the time and it wouldn't change with the RPM's. See if your mechanic can do what I suggested. For some reason, the #4 cylender is losing spark or fuel only at an idle. In my mind, it is an electrical issue. It could be ignition or a loss of power to an injector at idle. If the compression is good, don't let them rip into the engine.
See if they can run a scan during operation. The proper scanner will take pictures of everything that is happening that will then be reviewed by the tech to identify problems.
Monday, November 22nd, 2010 AT 2:24 AM