Hesitation Problem - Toyota Nation Forum : Toyota Car and Truck Forums

debased · 07-25-2011, 09:31 PM

New to the Community, looks like there's a bunch of great information here! I have a 2001 Corolla CE, manual, 180k miles. Had the front bank O2 sensor changed hoping to get rid of P0420 "check engine" code (didn't clear code). Ever since I've noticed hesitation when car is operating, especially when starting from a stop or switching gears. I had the CAT replaced (which fixed the "check engine" problem), but hesistation is still there. I've noticed that if I turn the car off after it's reached operating temp and turn it back on, the hesitation ceases and it drives fine. This has been going on for the last 2 months or so. Anyone else experience this or have any advice? It's much appreciated.

expertmax · 07-25-2011, 11:43 PM

Probably your Mass Air Flow is getting old.

Since it's not cheap, you should borrow one and try this time with the new MAF on.

It's strange because you don't have a code.

ManfredN · 07-26-2011, 07:25 AM

I am experiencing the same problem. Except I had oil leaks that caused the 02 sensor to foul up.

I cleaned my MAF sensor with MAF cleaner this morning. Hopefully that works again.

debased · 07-26-2011, 07:43 AM

Thanks for the tips. I know that when I took it in to get that CAT changed they looked at the MAF sensor and cleaned it thinking that could be the cause of the hesitation as well, but it still happens. What gets me is how this all started the day I got the front O2 sensor changed. I took it back to the shop that changed the O2 sensor and they said nothing they did would cause the hesitation. Could it be just a matter of switching out the back O2 sensor as well? I've only changed the front one so far. Also, my brother has a theory about a problem when the car changes from "open loop" operation to "closed loop" and that's why it runs fine if I restart the car.

ManfredN · 07-26-2011, 09:09 AM

Thats an interesting idea about the loop switches. I also had my knock sensor replaced the last time it was in the shop.

expertmax · 07-28-2011, 11:27 PM

Do you have any codes ?

Did they put OEM toyota o2 sensors ? Using aftermarket o2 sensors is highly not recommended in almost all vehicles.

landphil · 07-29-2011, 01:27 AM

Quote:

Originally Posted by debased

Also, my brother has a theory about a problem when the car changes from "open loop" operation to "closed loop" and that's why it runs fine if I restart the car.

The ECM will switch from closed loop to open look automatically as the engine warms up, provided it does warm up properly. A stuck open thermostat and resulting low coolant temperatures can cause the ECM to remain in closed loop mode longer or indefinitly. The O2 sensor signals are ignored by the ECM in closed loop, so your new O2 sensor sounds like it's probably OK if it runs good when restarted warm. The post-CAT O2 sensor monitors the catalyst efficiency only, so won't be the culprit here.

Have you checked spark plug condition (Iridium plugs don't all last 192,000 Km like the manual says), compression, air filter, fuel supply, and other basics?

debased · 07-29-2011, 10:28 AM

Thanks for the input.

Expertmax: I don't have any codes that I know of, it has passed inspection since this all this started (I don't think it passes w/ codes). I changed the O2 sensor and CAT to get rid of P0420 code. I did replace the O2 sensor with an aftermarket brand, I guess that might be an issue.

Landphil: Spark plugs and air filter have been changed in trying to troubleshoot. Haven't checked compression or fuel supply. If there were problems with these, wouldn't it cause issues even after warm restart?

Thanks again y'all

expertmax · 07-29-2011, 12:30 PM

I really think you should check your ECU because like landphil said, the ECM switches from open loop to closed loop. What if the ECU is "stuck" in closed loop ?

landphil · 07-29-2011, 11:51 PM

Quote:

Originally Posted by debased

Landphil: Spark plugs and air filter have been changed in trying to troubleshoot. Haven't checked compression or fuel supply. If there were problems with these, wouldn't it cause issues even after warm restart?

You're probably correct on that point, but you can never be too sure. Skipping the "simple" steps in troubleshooting is a common and costly mistake, and far too often the issue would have been found earlier if not skipped. If it were mine I'd at least check compression.