cruising w/o cruise control issue

[mankypurple]

My 08 yaris, automatic is having an issue. Every now and then it starts driving by itself. The cool light will come on and it will accelerate without my foot on the pedal. If I pop it in neutral it starts rev hunting bad. Or it idles really low and vibrates the car. I was thinking the pedal position sensor or throttle sensor might be to blame, but than again ive always owned manual minI coopers. This is my wifes car. I'm a little lost with its workings. Please help. Any advice is greatly appreciated.

[CTScott]

If the cool light comes on with the car warmed up, then the coolant temp sensor may be bad. The engine will idle at a higher RPM when the engine is cold (or the ECM thinks it is cold). If the cold light did not come on, then I would suspect the throttle position sensor.

[mankypurple]

When its actually cold it doesn't rev hunt or accelerate while in drive. I just noticed it was on everytime it acts up.

[Kar98]

Now there's something you absolutely need to have a qualified Toyota dealership looked at. Do. It. Now.

[CTScott]

When its actually cold it doesn't rev hunt or accelerate while in drive. I just noticed it was on everytime it acts up.

That is part of what makes me think the sensor is bad. The engine isn't cold, but the system is acting like it is, so it ends up fighting against itself to run rich for the cold, but at the same time it isn't running like it is cold, so it fights back to stoich. Do you per chance have an OBDII device that you can use to monitor what the ECM thinks the coolant temp really is?

[mankypurple]

At the moment, I do not. The check engine light is on. I'll get that scanned at autozone today if I can. See if that gives any clue.

[CTScott]

At the moment, I do not. The check engine light is on. I'll get that scanned at autozone today if I can. See if that gives any clue.

That would definitely help to narrow it down to either the coolant temp sensor or the throttle position sensor.

As mentioned above, if it really feels like it is running away, you should not risk it and should probably get it to Toyota ASAP.

[mankypurple]

well, turns out the cel was for the coolant temp sensor. I bought one. but im having trouble locating where it goes!

[CTScott]

well, turns out the cel was for the coolant temp sensor. I bought one. but im having trouble locating where it goes!

Take a look a few posts down in this thread for a picture of the location of it:

www.yarisworld.com/forums/showthread.php?t=37691

[mankypurple]

Alrighty. Found and replaced!!! But, it didn't fix my revving problem. :-( so I'm back to being lost

[CTScott]

Alrighty. Found and replaced!!! But, it didn't fix my revving problem. :-( so I'm back to being lost

Has the check engine light come back on since you replaced the coolant temp sensor?