Fluxuating RPM: Temp Sensor? MAF?

[codfizzle]

So I'm having this little problem with my engine RPMs jumping around by about 350 RPM.

I think the (running temperature) Idle spec is about 700-750 RPMs, right? Well my car does this thing where it will be idleing at about 730 RPM, and I will hear what sounds like a relay of some sort click on withing my dash, and when this happens, the RPM drop down to about 400 RPM.

And the times at wich this happens is completely random. For example, when the car is cold and I start it, it idles itself up to about 1500 RPM. Then, I'll hear that relay sounding click, and the RPMs will go down to about 1150 RPMs. Sometimes it will stay at this RPM for 5 or 10 or 30 seconds before it clicks again and idles itself back up to 1500 RPMs.

It happens when I'm driving, too. I will be driving along, cruising in 3rd gear (with the car fully warmed up) and suddenly it will click and my RPMs will drop and the engine will sputter for about half a second. A few second later, it will click again and be back to normal.

It's really wierd how seemingly random it is, too. Doesn't matter if the car is cold or warm, how fast I'm going, what accessories I have on. Seems completely random.

One thing I have noticed is that almost every time I hear that click and my RPMs fall, the A/C compressor pump kicks on (even though I don't have the heat OR A/C on) and then it kicks off again when my RPMs go back up the their normal range.

I'm guessing it's a sensor problem of some sort, but I don't know which one. And right now I can't afford to just start replacing sensors until I find the one that makes a difference. (Although I did recently replace my PCV valve and Knock sensor, but these didn't help my RPM problem.) Maybe the thermosensor in the A/C condenser under the passenger side dash?

I've read a few threads about similar problems people are having, but haven't found any definitive answers yet. If anyone has had this same problem and found out what it was, please let me know. Thanks!

[Legacy777]

Do you have the HVAC system on any of the defrost settings?

[codfizzle]

Yes. I wasn't sure if it was supposed to click around that much, but apparently so. Also, since I changed the coolant temp sensor, it doesn't do it as much.