I have a 1992 V6 Wagon with the 3VZ-FE engine, with 153K miles. With A/C on and most prominent at a stop light while in drive, the engine would experience a stutter or fairly hard intermittent shake. Hard enough sometimes that you have to stand on the brake pedal because the car almost wants to pull into the crosswalk. No other stalling/driveability issues and smooth once underway. I was told that it may be the front engine mount and indeed the whole engine seemed to rock in the bay quite noticeably when it stuttered. Anyways, I was about to pull the idle air control valve to check it but instead choose to spray some throttle cleaner at the throttle butterfly area. Did a lite wipe down as far as my fingers could reach and sprayed and wiped as much as I could the pivot and linkage hardware. The car runs great now and the issue has gone away. Hopefully this helps some one else as I was about to order an engine mount.