P0505 Jeep - Can not Clear P0505 code on 99 Wrangler.

Question

Check Engine light is on and gas gage will register either completely full or empty, P0505 code shows on reader. I clear the code with reader and gas gage will go to completely full (I have less than 3/4 tank). Then with out turning ignition of I start the Jeep. The Jeep runs fine (1000 RPMs, it's 29 deg outside) no Check Eng light. I turn the A/C on and the RPMs drop but return to where it was. Turn Engine off, turn ignition on and Check engine light is back with code P0505 and the gas gage will be at E or F, usually E. I have replaced the IAC X3 to be sure, replaced the PCM. I checked the wiring from PCM to IAC; No shorts to chassis, No shorts between wires, No breaks in wires, and no excessive resistance in wires (all wires < .4 ohms). Where to from here? Did I buy a bad PCM with the same problem as my original?

Answer 1

The IAC specification at operating temperature (closed loop ) is 500 to 900 RPM, + and - 100, This make the RPM correct, There was a TSB for idle undershoot, which caused stalling out when the engine was cold and a reflash was the solution, but in you case this is not the problem, Measure the IAC with the IAC disconnected measure pin 1 and 4 you should measure 50 to 60 ohms,same as 2 and 3,As for the fuel gauge this is seperate issue On the fuel guage going form full to empty at a ignition cycle meausre the gauge ground, of the instrument panel (there was a TSB about the gauge being erratic operation ground being at fault).You should measure 0 volts. no more that .5 volts