95 Neon - High Idle!? Please Help Me!

bretrichter

I have a 95 neon SOHC that drives with a very high Idle. Not all the time, but 85% of the time witch i find strange. This has been going on for the better part of a year and the car is almost undrivable. Its putting a hurting on my breaks for sure.

I had replaced the PCM 5 years ago. Replaced the timing belt 2 months ago. I have searched all around for vacuum leaks but am not able to find anything. I pulled the throttle body off and cleaned it very well. I replaced the IAC.

The car continues to idle out of control as if the IAC is wide open. The only way to get the car to idle correctly is to cover the idle hole in the throttle body 90% up with my finger. The guy at Auto Zone said if its not IAC or vacuum hoses, then I should start replacing sensors.

PLEASE HELP! How do i diagnose this problem?

bretrichter

looked online to see check engine light codes that I am getting:

12 Direct battery input to PCM was disconnected within the last 50 key-on cycles
32 EGR system failure
25 Idle air control motor circuits, target idle not reached (+/- 200),vacuum leak found
55 End of error messages (If you get this only, no errors were found)


12 and 55 i understand why. 32 sounds like maybe clean the EGR system? 25 I have no idea?

bretrichter

**Update**
because I was receiving engine code 25 i replaced all vacuum lines and then the throttle position sensor. turned it on and still running very high idle. I will be doing a smoke test this weekend to see if there is any leaks i missed, but im fairly sure i didn't since I replaced all the hoses.

Whats next?!

thecardoc3

With a code for the idle air control motor circuits the testing is best done with an oscilloscope. There are four wires between the idle air control motor and the PCM. Each pair of wires (Br/Wht, Yel/Blk) and (Gry/Red, Viol) are controlled in the same way.

Depending on which way the PCM wants to change the idle speed it applies power to one wire of each pair and then pulses the other one to ground. The PCM then switches both the powers and the pulsed ground commands inside each pair for the motor to be commanded in the opposite direction. Testing requires confirmation that the power and ground commands are being made by the PCM and that the wiring is intact all the way through the idle air control motor.