no fule in 4th cyl.at idle on 1998 Plym Neon

Have you run a scanner while the engine was running to see if there is a fuel or spark issue?

I have had this to a mechanic who scanned it and said that it was the egr valve which I changes and it did not help. I also was told that it was the o2 sensor was hanging up. A scan also reveiled that the vacuum was ok and the compresion check was ok. Could it be a broken valve spring. What should I check next? Could it be the computer, and how would I check for this?

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.

Thank you for your advise .... I will check with my mechanic and see if he can run the scan you have suggested.

Let me know what you find.

Joe

let me know what you find.