Bowtie30

I have an 88, automatic with 42K miles, all stock. Sometimes it seems to run fine, other times it will idle about 2-300 rpm faster than normal with a misfire. It has new plugs and wires and the cap and rotor look fine. I'm thinking the fast idle may be because the engine is getting a signal that it is still cold and therefore still on high idle. Any other idea's as to what to look for? Thanks.

65Z01

When the misfire occurs a timing light clipped in turn onto each plug wire would show if there is any coincidence with ignition firing.

An idle problem might be due to sticking/defective IAC valve.

Bowtie30

Thanks. I will check these out.