Rough idle, but no codes

[RyanR0101]

’99 Grand Am, 2.4L, non EGR. It has a rough idle, particularly when hot (low RPM, ~550) and in gear. Shaking is felt in the cabin. No issues cruising or when accelerating. Plenty of power. No codes set. The sound at the exhaust pipe has a “ting, ting, ting” mixed in with the normal expected “mmmm” of the exhaust sound. Plugs are brand new and didn’t change anything when they were installed. Belt tensioner is new also.

Any ideas what could be causing this? Maybe the IAC?

[toolguy]

Have you ever replaced the motor mounts? Just asking since you said there is shaking.

[RyanR0101]

Have you ever replaced the motor mounts? Just asking since you said there is shaking.

No, never did that. I can also hear the inconsistent exhaust tone in park or N though, which makes me think it's not motor mounts.

[toolguy]

Well motor mounts can cause vibrations. Test them by opening the hood, start the engine, put it in drive holding the brake pedal down and give it gas. Watch the engine and if it seems like its going to jump out of the engine bay, one or more mounts are bad.

Regarding the IAC. If you can get it out without breaking the mounting screws off, take it out and clean it and the cavity it goes to in the throttle body. Reinstall.

Otherwise, I do not have any more ideas.