Idle problems with A/C on (1 Viewer)

[LazySummerDays]

I just plowed through a pile of post regarding A/C issues and haven't come across anyone with my problem. My issue is when the A/C is running the engine will cycle it's idle speed between 600 and about 1000. It will slowly crawl upwards over about one minute and then sharply drop back down to regular idle speed, then repeat, as long as the A/C is running. The A/C itself works great. Living on the west coast of Canada it can easily get the temperature in my 80 to resemble a refrigerator, even on the lowest setting. No problem is evident when driving, just stopped and idling. My truck is a 94 US model with the stock 1fz. Any thoughts on where to start poking around?

Thanks

 

[superjuice]

Mine jumps to 1000 when the compressor comes on, then drops down to 700 when the compressor disengages. I don't think it should "ramp up" over a minute though. I believe there is an adjustment for the A/C idle, look at the throttle body and have someone kick on and off the A/C. You should see a vacuum diaphragm move the throttle somewhere. Maybe its sticking or something

 

[CJF]

My issue is when the A/C is running the engine will cycle it's idle speed between 600 and about 1000.

What is it you're thinking the idle should do with the A/C engaged?

 

[LazySummerDays]

What is it you're thinking the idle should do with the A/C engaged?

Like superjuice says, I imagine it would idle higher than when it's not engaged, but the idle constantly going up and down doesn't seem right.

Thanks for the start superjuice, this problem has been on the back burner for sometime. Hopefully I'll get around to paying it some real attention before summer.

 

[ppc]

The IAC - Idle Air Control increases the RPM when the AC is turned on/compressor is engaged and lowers the idle when the compressor shuts off. On a cooler day that could cycle once per minute. It should just step up the idle immediately and not gradually. The IAC opens an air passage in the throttle body to regulate rpm. It is what called a stepper motor. It sounds like that passage or entire throttle body needs to be clean. There are several threads you can search to get more details.