FIXED: Return of the P0171 and P0174

[upallnight]

Originally Posted by J.Belknap

Recommend after you swap the T-stat go on a good 10-20 minute highway cruise in 4th gear. Beat on it a little if you can give it load. The idea is to burn off carbon and condensation.

Edit: I would wager the next cold start after that will be better. Might sound kinda silly, and hell, i could be wrong BUT I've seen that symptom/fix before.

He got a P0171 and P0174 DTC. Kinda doubt if a bad thermostat will be giving him those codes. In fact like you mentioned that a cold thermostat will cause the engine to run rich.

Either a vacuum leak (could be from the injectors he removed but didn't replace with new o-rings) or a clogged filter or bad fuel pump. He replaced the filter and fuel pump so that just leave the injectors as a possible source for the vacuum leak.

To Quote Mr. Spock

" If you eliminate the impossible, whatever remains, however improbable, must be the truth. "