Been here, done this with other cars. Check connections. All connections, especially grounds. How'* your battery? You need a good, strong battery with good connections to help "filter" the voltage you get from the alternator, which is by its nature rather dirty DC voltage. Soooo many times I have scoured over someone'* car with this kind of funky stuff only to find a bad ground, or several. My first one was several years back, same kind of erratic stuff, no one could find it... turned out two wires were frayed in a big harness, and when they got wet, they would share information and cause a hell of a problem. All kinds of codes, weird codes, unrelated codes, stalling, rough.. spliced in a few new non-green and corroded wires, problem solved.
Electrical, electrical, electrical.. I've seen it a dozen times!! So many sensors get replaced for no reason...
just my 2 cents worth..
1993 Bonneville SE, frame off resto in progress, will be stock except painted black & chrome t-stars, estimated finish date - spring 2009.
Cars in my "fleet": the bonny project, the bonny parts car, 1999 Olds eighty-eight LS anniversary, 2004 chrys T & C.
Husband, father of two daughters, deer hunter and lover of most things GM, (although I do like my Chrysler minivan) - but nothing comes before my girls..
I'd much rather go home after work and be with my family than do anything else..