PontiacBonnevilleClub.com

Hey guys, first time poster here

I was wondering if anybody could tell me more about some strange things going on with my fuel trims on my 2000 SSEi. Car in question is totally stock with 133k on it. I've just recently bought it and have been going through it slowly with a fine tooth comb. The only engine work I've done so far is cleaning/disassembling the throttle body and cleaning the IAC and MAF, new air filter and cleaned the PCV valve. It has also had a CEL (PO0446) that I'm hoping I've fixed (vent valve was gunked up).

Anyways, fuel trims are new to me, but after looking at mine through the Torque app they seem to be all over the place. At idle, my LTFT's are usually 10-16%, STFT are usually pretty normal (0 to -3) but will swing +/- 10 while driving. At about 1500 RPMs, the LTFTs move back to 3-7, short terms are about the same, too. Then almost any RPMs after that they pretty much return to the 'idle' stats above. Can anybody tell me what gives? I'm thinking it looks like some kind of vacuum leak but the carb cleaner test around the intake and injectors yielded nothing. I've also noticed that my boost (@WOT) maxes out about 7.5psi. Seems like the normal is 9ish? Fuel pressure is about 40psi idle, 48 with a little throttle (regulator still hooked up). Car seems to run fine, no lights, no chugging. The only thing I've noticed is what feels like a miss in the first few seconds of a warm start-up.

What would make STFT's good (or swing that far out) but LTFTs say I'm dumping fuel?

There are some great YouTube videos on fuel trim that can really help you understand
and diagnose your engine. The videos can explain it better than I can.
Try Schrodingers Box. He knows his stuff.

STFT would change in response to throttle.
Your engine is running too lean.
In addition to the vacuum leaks that you've checked for---which can be as simple as a gummed up, sticking PCV valve---or a PCV valve that is missing 1 or both o rings-----it can be caused by faulty MAF or O2 sensor(s),dirty fuel injectors, fuel filter, a cracked vacuum hose (sometimes they crack on the side that you can't see) loose clamps on the air intake snorkel , a sticking EGR valve or a failing fuel pressure regulator or fuel pump.
I hope you used a cleaner made for MAF cleaning, as the other cleaners leave a residue that interferes with the MAF sensor being able to read the air flow correctly.

Hope this helps and that you will post your findings once the problem is solved.

an exhaust leak prior to the O2 sensor can also make the car think youre lean and add fuel.

The PCV looked original to the car... I'm thinking the O2 sensors are likely original to the car as well. MAF has a reman sticker on it but the data I get from it appears normal. I did clean it with the appropriate cleaner as well. I will have to crawl under there this weekend and look at the O2s and see if I can find any leaks while I'm there, fuel filter looks original, too. Thanks for the ideas!