My 90 4rnr cycles at stop lights, btwn 850 & 1300. If I "kick it down" (which I don't understand can be done with electric fuel injection) it will drop to 900 rpm. And over time, it is getting worse. Other-wise, the engine runs like a top. Is this the air flow sensor being clogged up by the use of a K&N air filter? The guy at NAPA said that would coat the sensor wire with oil that would throw it off. Other ideas?

OOOPS Red face, red face.:z: <img src="/forums/images/graemlins/zombie.gif" alt="" /> I clicked on "edit" as moderator on your post above instead of "reply" sorry.. meaning to post the following answer.....
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You NAPA guy would be correct if your Toyota used a hot wire MAF sensor, but I believe your '90 is a moving air vane type MAF sensor. K&N Filters can cause problems with the hot wire sensors, but the symptom of that is not what you have..

Your problem symptoms indicate that your throttle position switch is not electrically closing the contacts that indicate to the Engine ECU that the throttle is mechanically at idle..

Without this circuit going closed, the ECU will not go into the mode to regulate the idle speed or, some Toyota ECUs will literally oscillate the speed from 800 - 1300 rpm as you describe.. by out of control running the idle air control valve back and forth..

Many times this problem is caused by people mistakenly adjusting what looks like the idle speed screw on the throttle body, thinking that this will change the idle speed (NOT! on a ECU controlled Idle Air Valve controlled system)...

Wear on the throttle body shaft can also cause this problem to start happening, and symptomatic of the cause when "kicking" the throttle causes the problem to sometimes go away.

What looks like an idle speed adjustment screw is used to set a baseline clearance of the throttle body butterfly plate off the throttle wall by a spec'd amount in the procedure.. Then all other TPS adjustments are referenced to this. You need to go through the TPS switch adjustment process using the Toyota service procedure for this... If that don't work, you may need to replace the TPS switch..

Dang! Now that's a reply! Thank you for the prompt and insightful response. I'll go looking for the tps switch adjustment process you suggest.

TPS- root of all evil. Never forget, grasshoppa...

News, good and not necessarily so...I found TPS test instructions on 4crawler. According to their position ranges (0.0mm, 50mm, 77mm,WOT, etc. I was all within range (ohms respectively: 774, 895. infinity, 5.02k, and Vcc = 5.6k).

I went ahead and removed the throttle body and gave it a good cleaning (but not a disassembley). Since I have no gasket, it's on hold til tomorrow. I guess it may be dirt or wear. Thanks for your insight. I sure appreciate you guys!

Occurs to me that if it's not the TPS, what next? The throttle bore had a little wear, a thin line where the plate rests at zero (or almost zero).

Throttle air valve maybe? Don't know about the 3.0, but on the 22RE, the o-ring for the adjustment would rot and drive you nuts until you found it.

Throttle air valve. I'll look for it. Wish I had the factory manual. While I'm here: it seems as though the idle is set "too high" and the surging is more a momentary drop to a reasonable idle--800-900rpm. Would the fact that I plugged off the power steering "advance" on the power steering pump be causing this? Thanks in advance. I sure appreciate you guy sharing your experiences. It's a lot of help.

Plug it back in and see if there's a difference. BTW, the 93 FSM sticky'd in the early trucks section might be helpful.

Does throttle air valve go by any other names? I don't see it in any of my manuals.