JC III

Found out an odd thing working on our 87 4runner 22re this weekend doing a tuneup. The engine typically runs great now, but in the process of checking it over, while in park I slowly raised rpm up to 2K, at which point it immediately drops to 1500, then bounces back to 2K and continues bouncing back and forth between 1500-2000 as long as you hold the throttle at the position that would normally hold it at 2K. It does not do this when you first start up, only when warm. If you rev it quickly past 2K it works normally, only when you go slowly. I can only tell when it's in park, I cannot notice it when driving but that is also at a couple of typical shift points so it may be doing it under power too. It may have been doing it since we got it, I've never slowly revved it in park up to 2k before.

It's always a 500rpm drop exactly and repeatable at will, almost as if the injectors are cut right at 2 for exactly 500rpm on purpose, as if a function of design. Is this a typical function of the ecu or is there something wrong that I may justifying previously as simply the "anemic" 22re?

I installed a new tps about a week ago which resolve a lot of other problems, and new plugs (properly gapped), new wires (7mm bosch), new air filter this weekend, etc. Other than this 500rpm bounce under specific circumstances, it seems to run very well.

Thanks for your input.

4Crawler

iTrader: (3)

Could be a drop out or short in the resistance track at that point . That tricks the ECU into thinking you have closed the throttle, and it kills the fuel thinking you are slowing to a stop. Then after the RPMs drop below the threshold, it restores fuel to the injectors, RPMs rise and so on:
- http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

JC III

So you think a brand new TPS may have a "flat spot" in resistance at that one point? Didn't think of that. Thanks for that link: after reading your article, I'll measure resistance throughout the range and see if that is the case. Should be simple enough to do while it's on the vehicle using the gas pedal to slowly bring it through it's range of motion.

If it's not evident that is the case, I'm going to pull the TB off and thoroughly clean it, readjust the tps via your procedure and see what happens. I've looked everywhere for the screws you have on the site and couldn't find any so I ordered a set. I hope the guy that decided to put those phillips head screws in that position was fired right after someone realized it was a complete engineering "Homer Simpson"...."DOH!"

Thanks for your help.