Low Idle

Hello everyone,

I have a 2008 Toyota Corolla zre151 (european model) with a 1ZRFE engine and MMT transmission.

When the car is hot (after car warms up and at driving in high traffic in town with a lot of start and stop) when I come to a stop the RPM drops down to 550 and 1-2 seconds later start to go up to 650 before it stabilizes to 610 RPM. The Toyota dealers here are useless and I started to check the car my self and try to fix it. As I connected my laptop to the car using Toyota TIS, I noticed that the long term fuel trim was at +9% and short term fuel trim at 14%. The car was also sluggish.

I have changed all the vacuum hoses, the 2 O2 sensors, MAF sensor, EFI coolant temperature sensor, new spark plugs, PCV valve and hoses, and one way valve from the brake booster (including the grommet). The result is that the car drives better and the long term fuel trim is now at 0% and short term fuel trim at 0 to 4% but the problem with the idle persists and I am out of ideas.

One of the things I noticed while I recorded in TIS the engine parameters while I was doing a test drive is the fact that the O2S B1S1, O2S B1S2, O2 RL Switch time B1S1 and O2 LR Switch time B1S1 values go to 0 for 2-3 seconds and then slowly go back to normal. This was the same for the old sensor also. Please see attached file for the O2 B1S1 sensor. Is that normal? I do have to mention that my car has close loop, open loop and open drive loop modes. The phenomenon mentioned above happens in open drive loop and continues in close loop.

If you guys have any idea I really appreciate any advise or help.

Best regards,
Bogdan

Is this an electronic throttle body or does it have a throttle cable ? Have you cleaned throttle body and or idle air control valve?

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It is an electronic (drive by wire) throttle body. I have cleaned the throttle body and also changed the intake manifold gasket when I changed the PCV valve). I do not think the car has a idle control valve since is drive by wire.

Thanks

MMT is an electronically controlled manual transmission with a computer controlled clutch. Given everything you've thrown at it, I would be looking into delayed disengagement of that clutch. Total guess, but I'm steering away from it being a fueling issue and more of a driveline stall effect based on your trims.

The clutch is new 10.000 miles and it was installed by the dealer after a complain to toyota and it has all the recent updates (parts and software). I also suspected that for a while but if I pull the car out of the gear when it does it (as you said that maybe it did not disengaged) the RPM does not bounce up immediately it takes 3-5 seconds. It acts like it was not in gear anyway. I do not think it is the MMT because there are quite a few people that have same problem like me in the world and nobody found a solution to it. The low RPM problem is not constant. some times it does it and some other time it does not. If by chance when it does it I have a free piece of road in front of me and I floor it (5000 - 6000 RPM) then it does not do it again for a while.
I do not know if there is a problem that the O2 goes in 0 V and stays there for 2-5 seconds and that can cause this phenomenon.

If you guys have access to TIS software I can send the entire file from the test drive with the engine data.

I will be trying the week after next to pull out the injectors and have them clean with ultrasound and replace the o-rings. Maybe it is from them.

Thankks

Have you cleaned the throttle body ?

Yes throttle body cleaned 6 month ago and again today.