Idle problem, this one is very strange

[jsammari]

Hello,

This is my first post to this great site. My wife and I own a 97 XLT SOHC and for the past 2 years we have had this very annoying idle problem that nobody can fix.
When the truck is stopped and in gear, AND with the vent (hot or cold) or the A/C on, there's a very loud click under the hood followed by a drop in idle. This will happening every few seconds. As soon as we turn off the vent, A/C or heater, it stops. We have had the ISC replaced twice and the intake manifold gasket recall done with no luck. Any idea? Thanks.

 

[TPLYNCH]

That is normal Explorer behavior. The click is the compressor turing on (cycling). The compressor runs on all settings except Panel on your '97. It will cause idle to drop slightly. The Idle Air Control (IAC or AIC, depending on who you talk to) will then kick the RPM's back up so the engine doesn't stall. IF your engine is stalling when the compressor turns on, then your IAC is probably not functioning properly. Also, if you're low on freon, the compressor will cycle more often. May want to have the A/C system pressure checked.