1988 Z24 has uneven idle

[marc780]

This truck has 288,000 miles. Cat converter is practically new, did an in car overhaul incl valve job and new rings, fuel pump, less than 20,000 ago. Passes smog test with flying colors except they usually give me sh@#@ about the idle.

It has plenty of power, accelerates and runs on the freeway like new, and burns no oil. BUt Its had an uneven idle ("hunting") for about 100,000 miles! (It was doing this before and after the in-car O'haul). When cold it usually idles ok but as it warms up, the idle changes. It will start varying the idle speed. up-down-up-down. Its not serious but argg annoying!
Does anyone know what else i should check? please

[zanegrey]

try unplugging the temperture sending unit plug.

then start it and let it warm up.

if it acts as it did b4 the replace the temp sending unit.

good luck

[razeontherock]

Only 288k on it - is it even broken in yet?

My 87 has 360k. At 153 I had the thermo-electric unit replaced, also called the wax kit. It was supposed to fix it, but did nothing. Maybe I should check that sensor mentioned above - anybody know where it is?