Glad I found this site....
Im 27 and don't know much about fixing/diagnosing, my father is/was a take it to the dealership type. I blame him and always having newer financed vehicles for my lack of knowledge. But he is a good man.

I purchased my second Toyota 4x4 a week ago(1985 4Runner). Loving it so far, even with the rust, the wet floor and saggy back end. and the issue in question.

Heres my issue:
startup and warm up is fine, no issues at all. Warms up, needle jumps to 3/4th of the way up. Then settles back down to about a little less than 1/2 way. Continue driving w/o issue. Then the needle drops down to about 1/3rd(maybe a little less)... this is when the problem starts. I'm pretty sure that I burped all the air out of the system.

At idle: 750ish jumps to 1100ish(little less)..... the tach is aftermarket, the numbers might be off but the jumping/surging can be felt and heard. the surge jumps for about half a second.

so, at idle after motor is nice and hot(about 15-20minutes) it is surging, but smooth during warmup and initial 15minutes. very smooth, the reason I bought the vehicle. Maybe I should of taken it on a longer test drive?

when in gear and slight pedal pressure(maintaing/pacing speed on level ground) the truck will "buck".... when I gas it(accelerate normal) the surging goes away. with foot completely off pedal(while in gear) the surging is intermittent.

motor starts perfect whether warmed up or started for first time that day.

Also, after warmed up. When I attempt to hold a high idle(1700rpm, 2400rpm etc) it does the "surge" but it sounds like a "miss"(more than a surge.... rpm drops vs. surging higher in rpm)

would like to hear some opinions on what you think might be the issue.

Things I have done:
1)comp. test-204-207psi in all cyl(I can get the exact reading if needed)
2) changed to a 192degree thermostat(was doing same exact thing with 180degree thermostat, coolant temp gauge looked "too cold"(little less than 1/4 way up) so changed to the 192)
3) flushed cooling system, got gunk out of heater core, heater is uncomfortalby hot
4) seafoam treatment(brake booster method and in gas)

the surging issue was present before any tests/changes were performed.


the motor is a 22RE, I do have a cheap Digital Multi Meter and plan on using it if needed(although I don't know how to, I've only used it to test household batteries)....

TPS, AFM, temp sender????????? for some reason I think its a sensor and/or something to do with EFI. but have no clue where to start. Im hoping someone knows exactly where to start or has a strong feeling about where to start or how to go about diagnosing.

Hope everything made sense and I provided enough info.

Please any opinions/answers/advice will be appreciated.

thanks

 

Check the TPS, if its out of adjustment it can cause the problems your having. I would also be a good idea to change the fuel filter.

 

thanks for the reply....
unplugged TPS and it got a little better( fluctuating 200rpm at most vs 300-400rpm at idle) no bucking while driving....


plugged TPS back in and same results, surging isn't as bad(at idle), no bucking yet while driving. maybe computer is "resetting" after TPS was unplugged and plugged back in?.


it'll probably come back but is fine for now. Did more research, now think it is either TPS and/or AirValve(IAC)


TPS adjustment, IAC check is in the near future even if the problem has gone away.

 

The idle air control can go bad and not close all the way when the engine is warmed up, that could possible cause the problem your having. The idle air control is not a cheap part, last time i checked the price on one it was around two hundred dollars.

 

UPDATE to anyone who might ever stumble on this.

cleaned TB- lots of crap(black gunk), lower coolant(one that connects to IAC, I think) line clogged with something solid??? must of dislodged it when I flushed my cooling system numerous times(and it blocked the hole) after I bought the 4runner.

cleaned it out well with Carb cleaner. got whatever crud I could without getting too OCD.

took off IACV- cleaned out hoses(not much crap), technically the coolant hose going to the bottom of TB was clogged(but the crap was in the metal tube in the TB. not sure which way it flows)... checked resistance of IACV-PASSED, great don't have to buy a $200 part. Also, to check if the valve was opening and closing-heated up in sun(closes), then put in fridge/freezer for visual(opens). Maybe I was just imaging things, as I didn't measure it with any tools.


so far so good. no surging, slight fluctuating idle(+/- 50 rpm??) but think its normal. only have driven about 1 hr after work was completed.

I'll update again if the problem persists as I have only driven about 1 hr after work was completed.

still throwing code 7(TPS) but all is good for this weekend.

thanks to this link:
http://www.wildyoats.com/vbulletin/s...t=weird+idling

and to 4crawler's website