Just purchased a 1990 Toyota Deluxe pickup w/ 22RE engine, 4WD, 5SP manual. This truck runs well except that when it idles it goes from 2100 RPM & back to 1700 RPM every few seconds like clockwork. I have checked coolant level (told that could cause it), & it's full. Under power it feels fine, but even after warming up it cycles between maybe 500 & 900 RPM's. Just very annoying at a light! The exhaust is a little loud & others think I am going to pull a hole shot at the light! Any help would be appreciated! Mike

check your temp sending sensor

Maybe vacuum leak?

I had a problem like that going up and down and when i use to pre the gas pedal it will died a litle and then go and i just change the truotlebody sensor and that was it but i dont know if thats your case

Make sure the throttle body and/or butterfly valve is not gunked up with crap.

Your problem is the idle is set too high and possible timing advanced too far. set the idle with the screw on top of the plenum. idle at 800 rpm have the timing checked with a timing light. the throttle up valve and the main idle will fight each other if not set correctly. Get yourself a haynes manuel, just bought one for 18.00. It will tell you how to do all of this, its pretty simply after looking at the book.

One other thing to note is that when the a/c condensor is on, it will have a rolling idle.

STOP! Stop!

Don't do what anyone else has mentioned!

I am 99.9.999 percent sure it is your Throttle Position Sensor or better known as TPS. Just went through the same thing had the same advice as you from friends and Mechanics.

How I found out was relatively simple...

Take a 10 guage wire (about like a paper clip) and do a self diagnostics test under the hood. How you might ask?

Find the diagnostics box (just behind the battery) and connect the wire from TE-1 to E-1 and have someone hold it there.

Then having a pen and paper ready turn the key to the on position and get ready for the engine light to flash. The first flash as soon as you turn it will be just like when you start it normally. Then followed by several more flashes.

If it flashes 4 times a pause then 1 more time it is almost positively the TPS.

Note it may show several different codes such as 1 flash followed by 3 more which is more expensive and much more difficult. (distributor, computer, a short in the STA or NE circuit.

But as I finially discovered if you replace the TPS first it will probably cancel the other codes out, and is a lot cheaper.

Oh one more note to add. After you replace the TPS disconnect the negative battery terminal for a few seconds and then hook it back up. This will reset the engine diagnostic light and then you can repeat the diagnostic test to see if anything shows up again. If it flashes real fast don't panic that is a good thing. It means you fixed the peoblem! Hooray! If another code shows up then get your wallet out it may or may not be an expensive fix but you will stll have to pay...

Let me know how it works out for you