I noticed that when my AC is on, the car idle around 850-900. The car will compensate for the AC being by bring the rpms up to 1000 BUT only for a short period of time and it will do this periodically. I am wondering why doesn't my ECU keep the rpms up all the time when my AC is up at like 1000rpms. Just for reference my AC compressor was replaced before due to having problems with my AC. Any suggestions would be great, thanks.

 

I think that has to do with the Idle Stepper. Are you cammed?

 

Yup I am currently running the GSC S1. Another thing my vavle(think its called PCV) thats on the valve cover next to the oil cap, it looks like an L shaped and it slightly points down. Well when the AC is on and the rpms are around 850-900, that valve makes a rattling noise, the ball inside rattles around but once the rpms come up it goes away.

 

There is nothing wrong with your A/C. Thats just the way your car is tuned for the cams.

 

One last question then, how come when the AC is off the has no problem holding 1000rpm, which it was set to when the car was tuned. I am guessing that, when I was tuned, my tuner didn't bring up the rpms settings when the AC is on???

 

yea i have that same problem with my cammed evo....rpm's will drop lower when i turn a/c on and will adjust it self but then will end up dropping down in the rpm's again. and i hear that same noise also and it idles soo terribly rough. but i think alot of that has to do with my solid motor mounts

 

Every car does that. The A/C fan is turning on, hence the slight rev periodically. Perfectly normal.

 

+1

 

that is the compressor cycleing! ^^^ the fan only comes on when the compresor is on, there is no reason to pull air through the condensor if the compresor isn't running.

that is totally normal, the slight drop in rpm is the added load, the ecu can see compresor clutch active and bumps the rpm.

 

Indeed. They technically both come on the same time.