1998 3.0L Misfire on Cylinder 4

[gullpond]

I have a 3.0L 1998 Dodge Grand Caravan with just under 200,000 miles. When the engine is hot, it has an intermittent rough idle - sometimes the engine will idle fine when hot, sometimes it feels like it might stall, sometimes it just feels like it’s idling a little rough. When you increase the rpms to just above idle everything smoothes out. When cold the engine idles fine. The computer shows a misfire on cylinder #4. I have replaced the following: - Injectors - Sparkplugs – replaced with Bosch +4 - Sparkplug wires - Distributor cap - Rotor It still idled rough and threw the same misfire on cylinder 4 code, so I brought it into a local mechanic. He first said he couldn’t reproduce the problem (he checked it before the engine fully warmed up). Then he said it was carbon build up in the engine. Then he said he did a leak down test on cylinder 4 and that the compression was a little low. When I questioned why it only intermittently idled rough when hot and was fine when it was cold -- when you would think the compression would be the lowest and cause the most problems -- he just shrugged. Needless to say he didn’t instill a lot of confidence in his ability to diagnose the problem. I think the problem might be heat related which makes me think it might be electrical. Does anyone have any ideas? Steve

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[master tech]

The problem could be a valve seat, or valve guide.

[gullpond]

It could be, but why would it be okay when it's cold and the symptoms show up when it's warm? Will a standard compression test - not a leak down test - show a bad seat or valve?

I was thinking (hoping) it could be the ECM acting up when everything heats up.