[downrange]

When the car is cold it idles just fine.. But after its warmed up, the motor will rev up slow down, rev up, slow down. etc.. Like some one is just pressing and letting of the gas peddle. It doesn't rev a lot. Just a littlle back and forth. What's causeing this? Will also do this in gear when just coasting along..

[TxGreaseMonkey]

Possibilities:

. Check Ignition Control Module (ICM) or coil, which may be breaking down under heat. AutoZone can test each of these components for free. If the ICM has never been replaced, I would do it. Here's what it looks like and costs:

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. Check all vacuum hoses and connections. Particularly, check MAP Sensor hoses. Using soap and water, search for any other vacuum leaks.

. Check Idle Air Control Valve (IACV). It may need cleaning or replacing.

. Check alternator FR Signal/ECM--This signals the ECM when the alternator is charging. The problem could be with the ECM (perform K-Test, as a proxy for the ECM's overall health). There are other more involved tests that can be performed.

. Reset ECM and see if the problem goes away.