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I had a mild hunting idle, but enough to throw a P0507 code: Idle Control System RPM Higher Than Expected. Couldn't figure it out. Took it to the dealer, they said "cracked intake manifold -- $900 repair". I said "Here's your $125 diagnostic fee, thanks but no thanks" essentially. I asked how they determined the manifold was cracked. They said they sprayed carb cleaner around the throttle body, and RPMs increased. They didn't physically see a crack.
I pulled off the throttle body and cleaned that. The gasket looked to be in pretty rough shape so I cleaned up the two mating surfaces, and installed a new gasket.
The idle is now surging, but differently. Video included.
Kinda contradicts a different post I read...or I could be misunderstanding.
Completely cover the throttle body opening and it should die, if not there is a large vacuum leak.
If so cover the throttle body opening again, disconnect a vacuum line to the intake manifold and use a smoke machine to check for leaks.
You can make the smoker, there are diys on YouTube, or you can vape/smoke into the vac line.
We do this by starting the engine and covering throttle body opening. If it dies there is no vacuum leak. If it stays running there is a vacuum leak.
-if there is a leak, locate it and repair. (Can test with smoke machine as mentioned above)
-if there is no leak look inside the throttle body opening, find the IAC valve bypass port and block it. What are your results?
After this try unplugging the IACV and starting the car, what are your results?
We do this by starting the engine and covering throttle body opening. If it dies there is no vacuum leak. If it stays running there is a vacuum leak.
-if there is a leak, locate it and repair. (Can test with smoke machine as mentioned above)
-if there is no leak look inside the throttle body opening, find the IAC valve bypass port and block it. What are your results?
After this try unplugging the IACV and starting the car, what are your results?
Hey mac25 -- not sure if the videos are showing up, but I actually posted videos of both of these things.
When I cover the throttle body opening, the car dies.
When I cover the IAC port inside the throttle body, the car dies.
I will try unplugging the IACV and starting the car, and see what happens. What should I look for, depending on the result?
OK I unplugged IACV and started the car. It runs the same as before:
Idles normally until the fans kick on, and then once the fans kick on and it warms up, it starts the hunting/surging idle.
Did you replicate the dealership test, when your car is warm and acting up, spray carb cleaner in small shots at various places all along the intake manifold and pay attention for any sudden rise in idle?
One thing side effect of that test can also be that it suddenly “cools” down a sensor that was acting up when warm so it may “appear” to be a air leak but in fact a bad temp / pressure sensor on the intake.
Now would be a good time to buy/ borrow a live data reader and see what is being reported to the ECU.
06-09-2019
