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Engine Misfire And Hesitation



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Vehicle: 2002 Corolla 5sp, 180k miles

Problem history: Hesitation, burning 1qt of oil every 200 miles, P0420

Repair history: I rebuilt the engine, completely fixed the oil consumption problem, no problems with hesitation for several months (cold months)

Current issue: Recently, with the change to warmer weather it seems, my car has been having some hesitation issues again. After rebuilding the engine I still had the P0420, I thought it may be the catalytic converter but decided not to replace since the car was driving fine. Most of the places I drive take about 15-20 mins to get to which is about how long my car will drive without any issues. It literally drives flawlessly for 15-20 mins but then something changes (switch from open loop to closed loop?). When the issues start, the engine misfires, has lean/rich issues, jerky acceleration, etc. When this started I was curious on what codes it was throwing so I scanned and pulled P0300, P0302, P0125, P0135, P0420(always on), and P0505. I was like holy crap, what's going on. I thought since the car seemed to be running flawlessly initially (open loop?) and then having problems when it warmed up (closed loop?) it may be the front o2 sensor. I had changed out the o2 sensors with Denso's from rockauto when I rebuilt the engine. I decided to go ahead and replace the front sensor with a denso oem from toyota which helped the issue but has not fixed it. What else could cause this? The fact that I can drive 15-20 mins with perfect acceleration and idling and then switch over to misfiring/jerking accelerating/rough idling confuses me. I will be doing some more diagnostics after borrowing a good scan tool from a friend. Anything I should be looking for? Thanks.

The 1ZZ-FE was designed to light off the cat very quickly, usually gets into closed-loop mode in minutes. At 15-20 minutes, it is should be well past when it went into closed loop.

Definitely find out what it is doing with fuel immediately before and after it acts up. Specifically the LTFT and STFT - to see if those codes are truly being set of the ECM is on the fritz.

P0420 can be caused by a number of things - at the rate of oil consumption, car's age, and mileage - I wouldn't rule out a plugged catalytic converter. Double check that the exhaust is not leaking, especially close the upstream and down stream O2 sensors. This generation can eat up the two exhaust gaskets very easily - I've replaced mine twice so far. Can also be caused by a faulty heater in the downstream O2 sensor (your P0135 code) and the coolant temperature sensor (your P0125 code).

The P0505 code is interesting (IAC valve malfunction - on the throttle body) - could be the cause of the misfires, depending how and when it gets stuck. If you haven't given the throttle body a good cleaning, especially at the rate you were consuming oil - couldn't hurt to give it a good scrub on the inside. Same goes to the PCV system - double check the PCV valve, the grommet on the valve cover, and the flex hose - lots of oil blowby can clog the valve, plug the hose, and dry rot the grommet (if equipped).

P0300 and P0302 - random misfire and misfire on #2 cylinder. I'd pull the plugs to rule out any significant deposit buildup on the plugs. Can also be tripped via a bad coolant temp sensor. Make sure the igniter wires running to the individual plugs are not damaged, same with the connectors. Couldn't hurt to double check the charging system (make sure the battery has solid connections to the car) and that all chassis grounds are clean and tight. This engine is extremely sensitive to electrical noise - a dying battery, noisy electrical ground-loops introduced from an aftermarket sound system, bad wiring splices - can all cause the ECM to act screwy.

So with a scanner, my father-in-law and I watched the cylinders for misfires. Of course nothing while the engine was cool and then 15-20 mins later it started reading a constant misfire on cylinder 2 (P0302). So, we swapped coils with cylinder 4 and then got a constant misfire on cylinder 4. Looks like I have a bad ignition coil. I am hoping all the other codes are related to the misfire since they started at the same time. Kicking myself for spending $150 on an O2 sensor before running the scanner... oh well. I have ordered an ignition coil, crossing fingers.

Good to hear - hopefully that will fix the issue you are seeing. Don't kick yourself for the O2 sensor - always good to have a spare around for diagnostic work down the road. Since you are doing all the diagnostic work yourself, instead of a garage, you are already ahead - money wise.

Replaced ignition coil with new oem denso coil. Reset CEL, 45 min test drive and no hesitation, no misfires, no CEL. I'm expecting p0420 to come back but wouldn't miss it if not. Interestingly, the bad coil was not oem and the other 3 are all oem denso's. Somehow I never noticed this before. Here's to many unhindered miles ahead.