Q: Has a rough idle with no CEL on
Felt like a misfire, so I replaced plugs and wires. The issue was still there with idle dropping a little low after giving it gas and just a rough in general. Took it to a friend with a scanner because it had a check engine light on and the code was for cylinder #8 misfire. I swapped the coil to the #2 cylinder and then took it back to read but no CEL on. I did a vacuum test and it was at 18in hg and went to 21in hg at 2000 rpm. I took PCM fuse out turned key to start until I heard two chimes and then reinstalled. No CEL on and it drives great but when it's stopped, the idle is slightly rough. It's pretty minor, but it's not smooth like it was before.
My car has 111000 miles.
My car has an automatic transmission.
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I would try and have the fuel injectors and throttle body cleaned out. This should clean out injectors and intake valve carbon deposits that can cause the rough idle. If after driving the vehicle, and the CEL comes on, then have a mechanic diagnose the rough idle and do not disconnect or reset PCM unless directed to by a pinpoint test. This just puts the PCM in factory setting and may take a few weeks for it to see a problem again.
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