A couple of days ago, I finally got my old dinosaur laptop running XP to download and work with an old version of Toyota Techstream. Armed with that and a FSM, I started digging into finding out what is causing the high idle.
It was a little weird using a computer for diagnostics. This will definitely be a learning curve for me.
Anywho… I pulled the codes and found P0125. I cleared the code. Fired the truck up and played with the real time monitoring. That was very cool, but I really didn’t know what I was looking at. She was still idling high and my computer needed a reboot, so I unplugged it and started doing some “old school” diagnostics.
It looked like the throttle cable was at a funny angle, so I adjusted that. It’s in rough shape so that may need to be replaced at some point, but I know that is not the issue because I was running the engine with the throttle cable disconnected. Another suggestion was the IAC causing problems. With the engine running I unplugged the IAC and the engine instantly sounded funny and running rough. It didn’t die but I didn’t give it any throttle either. With that I know the IAC is doing something, just not sure what.
I drove her a bit (maybe a mile), just to see what would happen. The MIL was on, she wouldn’t idle down by herself, and I got light constant throttle hesitation twice. Got back to the house and plugged in Techstream. This time I got two codes: P0125 (again) and P0505.
P0505 sounded promising and there was a “freeze frame” stored showing what was going on when the trouble code happened. I wish I know what it all meant. LOL!
After that, I pulled out my FSM to see what it said about those codes in the diagnostics section. I got this:
And this:
So from what I can deduct, there is something going on with the O2 sensor upstream of the cat and an issue with the IAC. I had to move on to another project, so I put my tools away with the game plan of chasing the P0505 code first. That seemed like the correct path to fix the high idle. Then it occurred to me that I caused the P0505 code when I unplugged the IAC….
So, I guess I will start by chasing the P0125 code. LOL! That being said, does anyone have any experience with the upstream O2 sensor causing high idle? If you pull up to a stop sign, the idle will hang at 1500 or so. If you blip the throttle, the idle will drop to 600-ish and stay there until you give it gas again. I can replicate this in the garage, too, so it is not load dependent. Let me know what you guys think!