Ok, this is a strange one. I know my car and engine pretty well, so please take some shots at what you think this may be.. My car Idles fine in park and neutral. It also runs very strong and smooth. The problem is sometimes while idling in gear the lights will flash dim (noticed at night) for a second. The idle is brought way down and it sometimes sputters out and dies. It will start right back up and run fine. It seems to do this about every 5 to ten minutes or so or at about every 10th stop light. I believe either the air pump is shorted, the egr is bad, or perhaps the torque converter is trying to lock up? The alternater voltage drops at the same time this happens.. I will hook my laptop up and run lt1 edit on it tomorrow, but hopefully someone has some answers.. Thanks! btw, I cleaned the IAC with gumout. It will idle smooth in neutral or park all day.

 

Try disconnecting the EGR and plug it and see what happens.

 

The air pump only runs for about 2 minutes after a cold start so I doubt it's that. Could have an intermittent connection with the IAC harness, connector, etc.