I have a 98 Corolla with about 225k miles on it. Just recently i had about 7 check engine codes and i took it into the shop and they cleared up all but one PO125, insufficient coolant temperature for closed loop fuel control. That turned out to be the pre cat oxygen sensor so I replaced that. Immediately upon replacing the oxygen sensor the car began hesitating, i was driving up the road and all of a sudden i just lost all engine power, i had the gas all the way in and it wasn't accelerating at all, i had to pull off the road because it just wouldnt go. Well i turned the car off and then started it back up a few minutes later and it was doing fine. It mainly does it when i am going up a hill and the engine is cool and is just starting to warm up, like the temperature guage is about at the 1/4 mark. I notice that when the RPM's hit about 2500 the power just starts dropping off and its like the engine is bogged down, then as soon as it reaches 3k RPM it lurches back into full power, it does it in pretty much all the gears (its a stick). Once i have been driving, oh say a mile, it runs pretty much perfect. I have checked the vacuum, its fine. I have put sea foam in the fuel, engine block, and in the vacuum line, it hasnt helped. I took the fuel pump assembly out and dissassembled it and blew through it with an air compressor and a bunch of dirty fuel blew out. I put all that back together and it seemed to help a little bit, but it has since gone back to the way it was. I also replaced the valve gasket because it was old and leaking a little bit, but that had no affect either. I am thinking it has something to do with the emissions system because the problem hit as soon as i replaced the oxygen sensor. I am at a loss, i cannot figure out what is wrong. I dont want to just start guessing and replacing everything, i want to find the problem, and fix it.
You are right, thats always the first thing I suggest because I had such problems with mine, but anyway maybe the new o2 sensor was bad or something. My buddies truck had a problem like and it was one of his o2 sensors, or maybe its a problem with the cat being clogged up.
Do you know which O2 sensor they used to replace the old one with? If they used an aftermarket one or a universal type, you could have an impedance mismatch issue - which will confuse the ECM. I ran into a similar issue with my Matrix, replaced the OEM sensor with a Bosch direct fit, as I got it cheap - car ran "off" for weeks, finally sputtering and experiencing drivability issues - replaced it with a Denso O2 sensor - ran perfectly every since.
The fuel pump issue is more interesting. Which part did you blow through? Could be a bad fuel pump or bad fuel pressure regulator - may or may not be related to the O2 sensor replacement, as it could be just coincidence that the car starting to drive funny after replacing the sensor.
If you have your old O2 sensor - you can try throwing that back on to test out if it is a sensor impedance mismatch problem. If that doesn't do anything, then start looking at the fuel system.
Do you know which O2 sensor they used to replace the old one with? If they used an aftermarket one or a universal type, you could have an impedance mismatch issue - which will confuse the ECM. I ran into a similar issue with my Matrix, replaced the OEM sensor with a Bosch direct fit, as I got it cheap - car ran "off" for weeks, finally sputtering and experiencing drivability issues - replaced it with a Denso O2 sensor - ran perfectly every since.
The fuel pump issue is more interesting. Which part did you blow through? Could be a bad fuel pump or bad fuel pressure regulator - may or may not be related to the O2 sensor replacement, as it could be just coincidence that the car starting to drive funny after replacing the sensor.
If you have your old O2 sensor - you can try throwing that back on to test out if it is a sensor impedance mismatch problem. If that doesn't do anything, then start looking at the fuel system.
Yes the o2 sensor i put back on it was a bosche, i am going to check the fuel pressure this afternoon probably, if it turns out the fuel system is fine I will start looking into the O2 sensor more. The mechanics I work with do not think the new O2 sensor is the problem, they think it is probably the fuel system or cat converter. It has started having a hard time starting recently which leads me more towards a fuel system problem. Thanks for the detailed reply btw.
I had a similar problem not too long ago. It turned out that one spark plug was worn and severely out of spec. If you haven't changed them recently (and perhaps even if you have), it might be a good idea to remove your plugs to see if they're still good. Denso copper plugs (K16TR11) (factory-issue for 98 and 99 Corollas) are $2.50 a pop, shipped from RockAuto, and are good for 30K miles.
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Hesitation/Power Loss????
Linear Mode
