QUOTE (Jamchell @ Jun 3, 2010 - 9:29 PM)
You could try an in-line fuel injector cleaner. The type you remove a vacuum hose and feed into the engine while its running. Very possible you have 1 or more plugged injectors.
This is a really good idea, actually. It might not solve the problem, but it'll certainly help to eliminate potential causes, and you only stand to benefit from it. A lot of people on here have used Seafoam (it's a brand, not actual stuff from the ocean
) and I also highly recommend it. You can get it at most auto parts stores, Autozone, Oreilley's, etc. Fill up a CLEAN empty Gatorade Sport bottle or water bottle (the kind where the top pops up, not the kind w/the cap that unscrews) about halfway w/Seafoam, and cut the pop up top enough so you can fit a vacuum hose in. You can use your brake booster line. With the engine running, suck up the Seafoam, and don't be alarmed when all sorts of smoke pours out of your exhaust, and the engine stalls. This is normal.
Also, and I know this sounds kinda lame, but I actually had a very similar problem when I first got my Celica like 2+ years ago. I did everything to try to figure out what the heck was wrong with it, and it turned out to be the most obvious thing that of course I overlooked by overthinking it - I just needed new spark plug wires. When did you replace yours last? A basic tune up is ALWAYS beneficial as well as helps to further narrow down the possible culprit.