Hi Everyone,

On my 2005 F-150 with 174k on it. I've noticed for a while now that when my AC is on the idle pulls up to about 605-608 RPM on my Scangauge II and gets a bit rough and shaky. It doesn't throw a code and I know I have some odd psychological issue with vibrations, mechanics tell me some just do this and to deal with it. I've cleaned the MAF and Throttle Body twice since ownership, which did clean it up significantly but here was what happened yesterday:

I drove the truck in 80 degree weather for about 30 minutes. As I drove I noticed the idle was incrementally going up at stops, from 597 on the scan gauge to 612 RPM and when I reached my driveway i was at 624 RPM. I decided to stay in drive with my foot on the brake and observe the ODEII readout for a while. As I sat in drive (on a mild incline) the idle continued to increase steadily until it was at 736 RPM. Finally I put it in park and it was holding at 815 RPM, fully warmed up. I shut the AC off and waited for a bit so the compressor would shut down. By this point the idle hit 840 and the engine sounded like it was working under a light load, which I've never had happen before. I threw no codes and there was not exactly a BAD sound, just the engine sounding obviously under some load? I do have phaser knock and the like, but it hasn't caused any problems that I can identify at this time.

Any thoughts?

Thanks

 

What was the engine temp? The computer may be increasing RPMs to turn the cooling fan and water pump faster if the engine temp is rising to the upper limits.

 

This was my initial thought, but 80 degrees isn't super hot. My readouts were all within operating range and I shut the AC off, usually if there is a heat issue disabling the AC will adjust it over time. It continued to go up, regardless.