my 1999 4.3L 4x4 with 140k has developed the strangest problem. It will drive out fine for 5-10 minutes or so. Then I can watch the battery voltage climb from 12v to 16v and the airbag light will begin to flash and then go solid after a bit. At this time the engine will lose power and drop to 500 rpm or so and surge to 1200 rpm then drop back to 500 rpms and continue to surge as long as I attempt to accelerate. With the engine bucking in this fashion I shut it down for 30min to an hour for a rest period, after which I can make it home. At times it will idle just fine while other times it surge at idle as well.

I have not had a chance to have the codes read lately. There are a couple prior codes stored in there that come and go as they please without any trouble.

 

I had the alternator tested at oreillys and autozone and it failed 2/3 components at oreillys and I didn't get a breakdown of failures at the latter. At autozone I purchased their remanned unit and installed it. All seems good in the world again. The airbag light had not lit nor have a I noticed any battery voltage deviances. The engine surging is gone of course which I can surmise was caused by the failed alternator. At autozone the output os the alt was 25v where around 14v is the norm. My concern is whether I fixed the problem or rather just a symptom of an underlying issue. Crossing my fingers.........

 

Has the issue came back? I have the same year and model?

 

For me replacing the alternator took care of the problem. Good luck to you.