Toyota Repair: 1997 RAV4 IAC valve and TPS, haynes manual, resistance changes

Question
Before asking this question, I searched thru all of your answers to others that might be relevant.

My wife's RAV4 has an intermittent idle problem -- RPM's are sometimes as low as 300, other times as high as 2,400.  I noticed that when I disconnected the TPS, the idle would drop back to almost normal, about 900 rpm.  Of course, this would cause a 'check engine ' light and I would have crack the throttle open to start it.

This caused me to suspect the TPS, but from reading your replies to others it sounded like the IAC valve is sticking due to carbon build up.

I removed the throttle body and cleaned it.  I also removed the IAC valve and cleaned what appeared to be a 'rotary' type valve that is opened with a solenoid.  At the opposite end is a coil spring, similar to what is used in a household thermostat with a mercury switch, that I assume closes the IAC valve when no power is applied to the solenoid.

The problem is, after re-installing the throttle body, the engine ran at 2,200 rpm.  I removed the throttle body a second time, re-inspected the IAC valve, and installed the throttle body again, only to have the engine start and "idle" at 3,000 rpm!  Disconnecting the IAC brought the idle down to about 2K.

Unfortunately, the Haynes manual that I have does not have any diagnostic procedure for either the IAC valve or the TPS.

The IAC valve seems to be free to rotate thru about 60 degrees, from open to closed -- there does not appear to be any spring pressure keeping it in one position.  Also, I checked the TPS with a DMM.  I measured 4K ohms across the potentiometer (pin 1 to pin 4), but nothing else looks right.  When I move the throttle, the variable resistance changes from about 2K to 3K to infinite and back to 3K.  Also, the Haynes schematic shows what appears to be a normally closed single pole switch -- I could not find any switch using my meter.

So, my question is, how do I verify that either the IAC, TPS, or both, are defective?

Thank you,

Sherman Johnson
Middletown, MD  

Answer
A malfunctioning TPS will always trigger a check engine light, an IAC will not, reading your comment about not feeling any spring pressure on the valve doesn't right, the small door in the valve should normally be open about 1-2mm or less and should return when pushed open with a small screwdriver , if it stays open then that is your problem, you may have unhooked the return spring.