GaryDoug

New problem with the idle speed.. Yesterday my battery was dead due to me not shutting off the dash cam over the last 4 days. Jump started it with a battery charger. I noticed that the idle speed was very high about 1800 RPM and it took at least 1 minute to drop at all. In the meantime the idle was also fluctuating up and down. I had a code P0507 indicating a probable IAC valve performance failure. So I replaced the IAC valve with a new one and the code has not reappeared but not much has changed. When I do a cold start, the idle speed now goes to about 1500 and sticks there for about 10 seconds before dropping to normal ~900. This is new. Before, the idle speed cold was about 1200 and it took only a few seconds to drop. I performed the idle speed relearn procedure described in the FSM. No change. After the engine is warmed up for at least 10 minutes, it all settles down but before that, if I switch on AC or shift in or out of gear, the idle speed jumps up temporarily much more than before. I am thinking maybe a vacuum leak somewhere (PCV, EVAP purge ,EGR valve...?). Perhaps someone had this specific issue and can describe their experiences before I start checking parts. Thanks.

p.s. I just read the IAC counts and it was 10 at 575 RPM, 30 at 700 RPM, and 100 at 1500 RPM. Those seem very low.

Injuneer

Wonder if this is related to a problem with the RPM data from the crank or cam sensor? Reminds me of the LT1 issue with the MSD Opti - a sporadic pulse signal with an instantaneous ridiculously high RPM input to the PCM. The PCM responded by increasing the IAC counts, raising the RPM. The sporadic high RPM input happened frequently enough to never let the RPM to return to "normal", just kept jumping around. Never got any info from MSD on the problem, although they fixed it and sent replacement Opti to the guy with the problem (which failed right out of the box, but that's another story).

I suspect the dielectric properties of the epoxy used in the MSD cap were causing internal sparking that affected the optical module. MSD did state they made revisions to the cap and the module. Obviously no Opti involved with your situation, but perhaps whatever tells the PCM the engine RPM (crank or cam sensor?) is creating a similar problem. Just a wild guess.

GaryDoug

The problem has disappeared. 2 days ago I swapped PCM's just to make sure. There was no change. I left the spare pcm installed overnight and swapped back yesterday morning. After that, the engine ran normally with no unusual fluctuations. This time I did not perform the idle relearn procedure because I did not want to "jinx" it. Drove around an hour, let the car sit overnight and it works normally now under all conditions of in or out of gear and with or without the ac on. Today, still good with all the original parts installed