07 Corolla winter beater has misfire without CEL

TimboSlice

TimboSlice

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Need to pick your guys brain.

I have searched and searched and I seem to have found nothing. I originally had CEL for a Lean trouble code, and a miss fire. Here is what I replaced, spark plugs, intake gasket, fuel pump, MAF sensor, 02 sensor. None of these fixed the issue. I then replaced all of the injectors and the code has gone away. Here is the issue, now I have a misfire at idle and while slight pressure is on the pedal while traveling. There is no CEL!!! I removed the throttle body and cleaned it very well, I searched for a vacuum leak with sprays and propane. No leaks. I understand the mounts on these model cars tend to fail and trigger issues with idle vibrations ect. On my issue I can see the rpm's drop before the actual miss occurs. Thats why I am leaning away from the mounts, the bad mounts shouldnt make the RPMs fluctuate. Mine dont appear to be that bad anyways. I do have a small exhaust leak by the donut on the manifold. I also have not put new coils in. I decided not to put the coils in because I assume there would be a CEL on for a bad coil. Its only doing this when the car is warmed up. Most noticible at a stop light in Drive with foot on brake. Does not happen in Park. Does anyone have any suggestions?
 
Keep driving it. A CEL will come on, I guarantee it. Sometimes it just takes a while, but it will happen.
 
Could it be a bad (or at least dirty) IAC valve? I've dealt with that issue before on a couple of vehicles that had the same symptoms you're now describing (no CEL on 'em, either). Just a thought...
 
Squatch said:
Could it be a bad (or at least dirty) IAC valve? I've dealt with that issue before on a couple of vehicles that had the same symptoms you're now describing (no CEL on 'em, either). Just a thought...
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I hear ya man, but this throttle body does not have anything like that separate to check. it has coolant lines running through it to tell it when the car is warm and when to adjust, which I thought was pretty neat, and no surprise being Japanese and beyond intelligent, aside from a normal cleaning, the throttle bodies are something that is not common to fail if not ever according to my research. Also, when i unplug it I was shown what to look for if it was bad. Appreciate the input.
 
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TimboSlice said:
I hear ya man, but this throttle body does not have anything like that separate to check. it has coolant lines running through it to tell it when the car is warm and when to adjust, which I thought was pretty neat, and no surprise being Japanese and beyond intelligent, aside from a normal cleaning the throttle bodies are something that is not common to fail. Appreciate the input.
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Sorry for the bad info, brother. I'm not really familiar with the Toyota set-up, but it sounds like you are. (y) Sure hope you get it figured out soon. It sucks when your ride has nagging issues like that. Keep us posted on what you discover. Best of luck!
 
Squatch said:
Sorry for the bad info, brother. I'm not really familiar with the Toyota set-up, but it sounds like you are. (y) Sure hope you get it figured out soon. It sucks when your ride has nagging issues like that. Keep us posted on what you discover. Best of luck!
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Certainly not bad info! On any normal throttle body I feel you would have been pointing me into the solution. I cant explain how frustrating this has been. Frustrating enough to swallow my pride and bring it up on here. lol
 
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DI Ignition coils can definitely do this. Try to see if there is a procedure to check them with a multimeter for integrity. If you knew the cylinder acting up, you could swap to test. Perhap buy one and swap one at at time. All 4 would likely not be bad at the same time.
 
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mots said:
DI Ignition coils can definitely do this. Try to see if there is a procedure to check them with a multimeter for integrity. If you new the cylinder acting up, you could swap to test. Perhap buy one and swap one at at time. All 4 would likely not be bad at the same time.
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Intresting....I dont know the cylinder but I think I will buy one and move it around. I guess I could try and mock the issue by putting the car in gear with the e brake applied and using a temp gun to see which cylinder is colder.
 
Theres a TSB for p0171, looks like the fix is the intake manifold gasket, and it specifically calls out subfreezing temps which I bet you Winconsonians get. Might be worth a shot, doesn't seem too difficult. Also note that the TSB calls out an updated part #, so if you end up trying it make sure you get a factory gasket w/ the new part # rather than aftermarket.
 

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qslim said:
Theres a TSB for p0171, looks like the fix is the intake manifold gasket, and it specifically calls out subfreezing temps which I bet you Winconsonians get. Might be worth a shot, doesn't seem too difficult. Also note that the TSB calls out an updated part #, so if you end up trying it make sure you get a factory gasket w/ the new part # rather than aftermarket.
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I had already changed the intake manifold gasket. The P0171 code remained on until I did the injectors. Had the battery and alternator tested today also. These checked out fine. This made me spray down the intake manifold while running the car to see if the gasket I used isnt holding up. No leaks. Im going to see if I can get numbers for a resistance test on the coils. Its the only thing I haven't done.
 
Squatch said:
I'm rather surprised that this didn't result in a CEL. On three of my vehicles that had a bad coil, each resulted in a CEL and a code that said which cylinder it was. Did yours?
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That is unusual, typically modern OBDII systems are pretty good at detecting and flagging misfires, but not always. Here's an excerpt and link to an article on one of my favorite sites, it has a good explainer on how OBDII monitors misfires:
https://www.underhoodservice.com/tech-feature-detecting-misfires-in-obd-ii-engines/
Any misfires that are detected are recorded and tracked over time. If the rate of misfires exceeds a certain threshold, the OBD II logic is programmed to log it as a potential emissions failure and set a misfire fault code. The check engine light comes on and a P030X is set where X corresponds to the cylinder that is misfiring.

A code P0302, for example, would tell you cylinder number two is misfiring. If more than one cylinder is misfiring, there will be additional codes for those cylinders as well. And if a misfire is random and jumps from cylinder to cylinder, you may find a P0300 random misfire code.

On most applications, OBD II uses a “block learn” strategy to track misfires. Any misfires that occur are recorded every 200 revolutions of the crankshaft. The tally is stored in 16 memory blocks, so every 3,200 rpm the misfire count starts over again.

As long as the number of misfires in any given memory block remains below a certain value, there is no problem and OBD II gives that block a “pass” rating. But if the number of misfires in that block is too high, the block receives a “fail” rating. By averaging the pass/fail ratings of all 16 blocks, the OBD II system gets the big picture of what’s actually going on. This helps avoid the setting of false misfire codes, and also allows the system to spot pattern misfires that may cause an increase in emissions or damage to the catalytic converter.
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