Customers Vehicle: 2006 Chevy G3500 Express (Box Truck)
Engine Size: 6.0L
Complaint: High Engine RPM and Check Engine Light On
Previous Work: New Map Sensor, TPS and Both Upstream O2 Sensors
Problem: Engine is idling at 3,300 rpm and will not idle down
Shop Work Performed:
1) Computer Diagnostics and Scan for Codes
Code P0507 - Idle Air Control System RPM Higher Than Expected
A vacuum leak : Leaking air intake after the throttle body, EGR valve leaking vacuum, A faulty positive crankcase ventilation (PCV) valve
Damaged/failed/dirty throttle body
Failed EVAP system
Failed IAC (idle air controller) or faulty IAC circuit
We used Brake Wash (flammable) to spray around potential vacuum leak areas and came up empty. We hooked up a smoke machine to confirm there were no vacuum leaks and test was positive for no vacuum leaks.
We removed the throttle body and inspected and found an extremely clean throttle body. While it was of we cycled the key and watched the IAC valve to see if it was stuck. It looked like it wasn't moving as it should... but did move some. With our Scan tool attached, we could see the IAC circuit was not functioning as it should.
THE PROBLEM FOUND AND FIXED
We then Isolated the IAC wiring from the IAC valve and the pcm and checked continuity and found two wires had none going and if we wiggled the harness, sometimes it would. We found the two wires had broken inside less than an inch form the plug in at the IAC valve, We repaired the wiring by soldering them and tested. FIXED!!! Runs great and customer is happy....