Quote:
Originally Posted by Compelica
Figured that it would be applicable to post this here in the Software Tuning section as we deal with these issues more often.
After a reflash the ECU takes some time to relearn fuel trims, and those trims learn completely after a consistent amount of driving. But idle stability was one thing I could never predict - it would take a varied amount of time to get the idle to stop hunting with the AC on, and the RPMs would do engine shuddering dips after rising upon a slight tap on the throttle.
So I came across this extended OBD2 PID called 'Deposit Loss Flow'. As a background - the throttle body has carbon deposits caked onto the walls or onto the butterfly valve which impedes air flow. As a result, the TB must compensate with a larger opening to maintain the target idle speed. It is solely my guess here but the throttle body can easily adapt its opening during extended idle but it has to learn this position on where to 'settle' during rapid movements of the throttle.
Upon a reflash, this PID value would always be 0 grams per sec, indicating there is no compensation (subsequently opening of TB) done. 500 kilometers of driving and it still showed 0. Which then I found this particular bit in another Toyota service manual:
And it works. Followed the procedure to the dot, and right after the last step after starting the engine the learned values finally came up and my idle smoothened out. I'm happy once again 
Also, be sure to do this procedure without the AC on. Also you would want the idle to be as stable as possible during the warm up period so turning off lights and head unit may probably help. Hope this works for you guys trying to fix your idle |
Interesting, so this procedure is like a band aid if you have a dirty throttle valve.
If you have to go through this procedure, and it actually works, you now know your throttle valve is probably dirty, wouldn't it be a good idea at this point to just disassemble and clean the throttle body and valve, then reset the ECU?