Rough idle

I have a 94 mercury tracer, that Ive had for 15 years now. I recently had the head replaced, new valves, gasket etc. About a two weeks ago my car started idling really roughly, but only when I start it in the morning after its been off all night. Its start with no problem but it idles really, really roughly to the point that the whole car shakes. Then after a few seconds it smooths out and runs fine. I think it might be the 02 sensor.

Timothy Plump columbus GA

Nope, the oxygen sensor has no effect until the engine warms up a bit and goes into “closed loop” mode.

Other things to check: coolant temperature sensor connection (some cars have two; you want the one for the computer not the gauge/idiot light), idle air controller, leaking fuel injector.

Forgot to ask: Does the “Check Engine” light come on?

ahh. I recently replaced the coolant temp sensor too. but im not sure which one. and no the check engine light does not come on.