My Celica has 230,000 miles, A/T. Starts up fine. Idles OK. However noticed a slight stumble, hesitation, very mild bucking. Notice it more at highway speed, typically around 2,000-25000 rpm's. Floor it and it takes off like a scolded cat. No engine codes.
So far, replaced battery, spark plugs and wires, air filter, fuel filter, distributor cap and rotor, PCV valve, checked for head gasket leak. Is not burning engine oil. No apparent vacuum leaks. I have a cheap scan tool and nothing obvious from that, no misfires etc.. Also ran through some expensive fuel injector cleaner.
It's something I can live with but obviously prefer to try and fix because it's annoying and worried it may cause problems to other components. I also do not want to get into the trap of replacing parts based on guesswork, the stuff I've done so far is all relatively cheap but do not want to be replacing things like a fuel pump and injectors unless I know they are dud. Would an Auto Zone scan tool diagnose the problem I'm wondering?
Thanks in advance.
Check your iac, gaskets for throttle and manifold and for vacuum leaks. I know you said you checked for vacuum but check again it might be very small. Try cleaning your throttle body it may help some.
Thanks. Yes already cleaned throttle body. yeah will double check for vacuum leaks and look into potential of fault with IAC.
Don't forget to consider the ignition coil.
"stumbling, bucking" at those rpms makes it a possibility but like you said you don't want to just throw parts at the Celica and hope to get lucky.
Maybe grab a multimeter and check the resistance between the + and - terminals on the Primary side of the ignition coil and between the Primary and Secondary side of the coil.
It won't cost anything except a little time.
On that 4 cylinder Celica the Primary Side between the + and - terminals, on a cold engine ((cold ignition coil)), should be between 0.36 and 0.55 ohms. The measurement on a warm engine should be between 0.45 and 0.65 ohms.
Between the Primary Side and the Secondary Side of the coil the measurement should be between 9kΩ (9 kiloohms) and 15kΩ if the engine is cold. The measurement should be between 11.4kΩ and 18.1kΩ if the engine is hot.
Good information. It could be any of a number of things I guess. I have another theory. I bought the car in October. It was part of an estate sale after the passing of the owner. Only paid $1200. Not sure how long the car was sitting. He died in March so I'm guessing a minimum of 6 months, plus the time I kept it inside our garage over winter so the same half tank of gas was in the car for over a year. I'm thinking maybe the gasoline went bad and is affecting the overall running of the car, and it's progressively getting worse as it feeds through the system? Already added fuel injector cleaner, will buy some fuel treatment stuff and add that to the tank, have also filled it with Shell high octane. If things do not improve I'll take it up the road to Pine Hollow Diagnostics in State College, the proprietor Ivan is an absolute genius, check out his Youtube channel, I have yet to see him fail at diagnosing, and for $150 he will remove any further guesswork as to what is wrong. Thanks for your help, I will update asap.
I've watched Ivan Temnykh's videos for years. The guy is excellent. Keep us posted on how this turns out. (maybe he'll make a video of your repair)
Thanks will do. Luckily he is only an hour away, he is that good I've seen customers drive from halfway across the country to see him, a real car diagnostic guru! Agree it would be great if he made a video of it also.
Get your fuel pump pressure tested. Do you have a MAP sensor? If so, it's probably really dirty.
Yeah I think there's a MAP sensor. Will look into this and will eventually get fuel pump pressure tested. Going to call into Autozone and just for kicks use their scan tool to see if it picks up anything weird. Also ask them about whether they loan out fuel pressure pump testers. Thanks
These have a map sensor. I'm pretty sure they don't have a maf but I could be mistaken.
Thanks! MAP sensor only, $35 at Autozone
Thanks for all of your input. Replaced the fuel pump and problem solved, start up is much livelier and no more stuttering especially when going up hills, the old pump must have been on it's way out. Pretty straightforward job although took me much longer than it should have, but that's the way I work, prefer to take my time so I don't miss anything or fit incorrectly. Replaced it with a Denso kit which with postage cost less than $100 from Rock Auto. It's a relief because it could have been any number of things.