Quote Originally Posted by etlsport View Post
spoke to the shop again.. guy said voltage spiking is from loose battery terminals and that the transmission is stuck in 3rd gear which causes the lack of power.. still having trouble wrapping my head around that.. would it cause an idle of 2k rpms?

it also doesnt explain why the problem went away without the swrpentine belt

could third gear be a function of limp mode?

still perplexed by no cel or check trans codes
I think this guy is on the right track. Loose battery terminals (or electrical connections in general) would make the alternator think the battery has no charge, and it would increase it's output as a result. The loose/bad connection would make the ECU think there's a problem in the system somewhere because sensor(s) wouldn't be seeing the voltage they are supposed to, potentially putting the vehicle into limp-mode. And taking the serpentine belt off would have stopped the alternator from being able to produce the voltage spikes to the system.

Doing simple continuity checks starting with some of the main cables and connections (battery posts and terminals, starter, etc) might be a good place to start. Our battery post connections aren't the most substantial looking connectors, so getting a battery post wire brush and cleaning both the posts and the connectors would be what I'd do first. And once you got them cleaned, applying some dielectric grease as an aid in preventing future oxidation would also be worthwhile.