Rough idle in drive but only when sitting at a stoplight

[vt_maverick]

Update... I shut off the A/C on the way to work this morning and had no problems. Flipped it on at the stoplight just before our parking lot and the sound came right back. So does that change the diagnosis? I haven't pulled the ABS fuse yet, probably do that on the way home.

[Bob Barker]

Update... I shut off the A/C on the way to work this morning and had no problems. Flipped it on at the stoplight just before our parking lot and the sound came right back. So does that change the diagnosis? I haven't pulled the ABS fuse yet, probably do that on the way home.

That makes me think it's a vibration somewhere. If the load on the engine changes and makes the noise come and go then I immediately think vibration. It's still a free check to pull the ABS fuses and then test for vibrations with/without a/c.