How many miles on the car? How old is the O2 sensor? After replacing the MAF, plugs/wires/coil connectors on my '93 it ran pretty good but still had a lumpy, hunting idle. No codes though. Replacing the 110K mile/13 year old O2 sensor made it perfect. They can be bad enough to affect running without setting a code. Now it idles so smooth I can barely tell the engine is running. I don't know of any way to diagnose other than replacing, unfortunately. The sensor is $100+, but at least it's easy to install.

- JimY