Celica Forums Thread Like Summary - Can't figure out what's wrong

Hey guys! So I've got a 2004 Celica GT w about 165k, and for the past 2 years or so that I've had it the check engine light has been kinda on and off. I keep taking it in to get things fixed, but nothing has turned it off all the way. I've gotten various different codes, like P0012 for the cam shaft sensor which only came on once, and then P0171 which looks like a common one.

At first I thought it was the fuel injectors that needed to be replaced, so I ended up getting those replaced but the light was probably only off for a day or two after resetting it. Next, someone told me I would need a new catalytic converter, which seemed to make sense, but i put that off a little bit and ended up taking it to someone else to get a used one put in but then they ended up just saying some part of it needed to be welded or something I believe? I've gotta look back at my receipts to see what else I've had done in the meantime, but moral of the story is every time I take it in it appears to be something different.

The car itself has driven fine the past 2 years, except it burns oil reallyyy quickly. I drive it back and forth to Boston a bit for school, and I usually have to buy oil before the drive to fill put a few quarts in before I get there. I get the oil changed regularly and always check it and my fluids before going on long drives. I drove it from Chicago to Buffalo once, and on the way back from that I heard a pop and the back bumper by the exhaust pipe was totally black, covered in exhaust. It usually gets that way on long drives, which I assume is related to how its burning through the oil. That's why catalytic converter made sense, but the back and forth opinion is driving me crazy. A mechanic told me it was normal for Toyotas to burn through oil that quick because of the engine, but that also happened to be the same guy I bought the car from so not sure if thats true or not.

Someone I know who works on cars suggested it might be a blown head gasket? But I feel like I wouldn't be driving around as normally as I am now with something like that.

Any insight or ideas on what I could have going on and what I should get looked at? I've got the money to spend and just want to get it all figured out and fixed up so I can drive it around worry free.

Also - anyone in the Buffalo area know a good place to take Celicas into? I'm also sick of hopping from mechanic to mechanic - just want to find one I can trust.

Thanks!!

P0171 is intake manifold too lean.

There may be leaks in the few black rubber hoses between the air filter box to the intake manifold.

But most likely your Mass Airflow Sensor on top of the air intake hose are dirty or defective. Swap in a known good DENSO MAS. All Toyota and Lexus use the same DENSO MAS. You may try to clean the sensing element with a non-residue contact cleaner, but this sensor sometimes are bad even if it looks good and passes electrical tests.

If not the MAS then there may be cracks or leaks in rubber air and vacuum hoses between the air box and the air intake which are a pain to find.. Check all rubber hoses to make sure they are not cracked or broken, and all plugged in securely. If that does not solve the P0171 problem then you may have to blow smoke in the air intake and look for leaks, a pain in the ass..

The 1ZZ engine is known for burning oil. A few quarts for 500 miles drive is way too high, may be caused by stuck piston rings or stuck valves due to oil sludge.. Try to clean the engine and get rid of the oil sludge by flushing with MOTOR MEDIC'S motor flush (Walmart $5). I would use half recommended strength, put half a quart in the engine, idle for 20 minutes then dump the oil and replace oil and filter. You should see the dumped oil black and thick like tar. Drive a few weeks then repeat the flushing a couple times to really flush out the sludge and see if it run better burn less oil.

My Celica GTS with 300K miles was running rough with low compression in CYL1 due to infrequent oil changes. Shops kept telling me there was no fix, I had to swap an engine. 2 motor flushes with oil changes later, compression was up high and even, engine ran smooth like new again LOL..

Dont let the stupid shops rip you off.
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Thanks for the advice!! Ive got some time now so I'm trying to do some research and see what things I can clean and take a look at myself. You mentioned possibly needing to replace the air flow sensor, how do you know when it just needs to be cleaned versus replaced? I'm going to buy a cleaner for it and give that a try soon.

People also recommended checking my air filter which I'll probably do at the same time (and discovered I don't have a cabin air filter, so working on that too)! The intake was mentioned along with that, but I think thats definitely too complicated for me to check out myself, I'll leave that to the pros.

Some had mentioned checking and replacing my piston rings, as well as my PCV valve and oil control valve? I'm not sure exactly what those are or what they do, but I'm looking into that a bit! Learning a lot for sure.

Thanks again for your help!