I have a 99 montero sport limited 4wd 3.5 litre. the other day when i started it up the idle was around 300 rpm and it was hard to keep it running. when it warmed up it was good. also the AC was making a lound clicking noise. I adjusted the idle up to around 700 rpm so I can still drive it but once it warms up the rpm is at 1100 also before this issue, when I turned the AC on the rpm would rise a little to compensate for the engine load. now with AC on rpm drops. I did a resistence test on the IAC motor terminals and they read 29.1/29.4/29.6/29.0. Are these good readers or not? what else could be the problem? please HELP

 

I had a similar problem on my Limited 3.5, and initially did the same thing as you by pushing the idle up (I cranked the screw on the cable to do it).

Tried a bunch of stuff thinking it was a vacuum leak or something. Finally, when it was due for timing belt I replaced plug wires and plugs and plug seals and PCV etc. Got top of the line Iridium, don't go cheap on Montero plugs...ever!

That's what fixed it. Now at 148K it purrs and idles like new.

A/C will always cause the idle to drop momentarily and the fan clutch noise is significant, but not a problem.