wii_tarded

hey all, need help.
'91 4Runner, 3.0 manual 4wd.
after the truck is started and warms up, it can't seem to find where it wants to idle. The tach literally bounces from 1100 to 1800. That's only at idle. This started yesterday with the coldest it's been here this winter, (12 degrees) and continues today (7 degrees) Is this a weather related problem, or is it a real problem. btw-I have an exhaust leak and dunno if that contributes to the issue.

Flash319

Your idle is to high after it warms up, or you have low coolent/air in coolent system. You may have a high idle do to vacuum leak. When the ECU comes out of closed loop (running temp) the idle must be under 1000rpm or it starts hunting.

toyota4x4907

Yeah, low coolant with air in the system will do this. Same thing happened to me before I replaced the radiator because it was leaking so bad.
Also, the coolant temp sensor or the idle air control valve could be going bad.
Most likely its low coolant though.

wii_tarded

Replaced the radiator 2-3 months back. Coolant system is solid. It's not idling high or low, it's bouncing back and forth, just as if you were tapping the gas pedal. During warm-up, it idles great, driving is smooth. The sensors, where are they, and how do you tell if their bad?

yoder519

mine does the same thing, its done for a while. and im just a hop skip and jump from in in bristol va. but anyways mine does it when i first start sometimes, then itl do while im driving it and gives itself gas. does yours do that?

abecedarian

A 'hunting' idle is an indication of a vacuum leak. Given that the idle is 'stable' when cold started doesn't mean much since the rich fuel mixture the ECU uses while the engine is warming up masks vacuum leaks pretty well until the engine warms up.
However, a fluctuation of 700 rpms would be a significant vacuum leak.
I'd start by figuring out that exhaust leak- they cause air to be drawn into the exhaust: in spite of the fact it sounds like exhaust is being blown out, that only happens when an exhaust pulse passed the leak- otherwise there is 'suction' on the leak drawing air into the exhaust. Intermittent lean/rich/lean signals can mess with the ECU when in closed loop mode... and here we enter another problem: the ECU is only 'closed loop' when the throttle is open (but not WOT {wide open throttle}) and the engine coolant temp is above around 140F. So this implies there may be a problem with the TPS adjustment or maybe the coolant temp sensor.
Don't quote me on this, but this is where I'd start.

SMOD

I had this problem with my 92 Honda Prelude. It idled up and down until it would die. lol.

I don't know if it would be the same on the 4Runners... I've only owned one for about 2 months so I don't know a lot about them yet... but the prelude problem was the TPS (Throttle Position Sensor). It turns out it was shot so it would send 0 volts sometimes to the ecu causing it to rev up and down.

xXbrutalXcoreXx

does your idle surge when the A/C is on by any chance? I know you have a 3.0 but the reason i ask is because my 22r only surges like that when the A/C is on. There might be some similarities between the two.

nv4runner

Your engine is supposed to idle up when the A/C compressor kicks on and back down when it turns off.

OutlawMike

My first post on YT, I have been hanging at 4x4Wire for few years, making the transition over here.

I had a similar problem with my '89 3.0 Runner after a rebuild. Coasting down a hill or idling while stopped the tach would bounce.

I traced it down to my TPS sensor. The sensor itself was not bad and it measured out to within the FSM spec's, but when I adjusted it to be more "touchy" at idle, the issue went away.

The TPS has four contacts to the harness. The FSM has a procudure for how to measure the resistance at each contact. Two of the resistance measurements specified are done with a fealer gage in between the throttle stop. One is at .5 mm and one is at .75 mm. When the measurement is done with the throttle spaced open .5 mm you are supposed to measure resistance less than a spec'd amount (2.2 kOhms off the top of my head, check that spec, do not take my word for it). When measuring at .75 mm offset you should have infinity.

I had my TPS set so that it was measuring less than 100 Ohms at .5 offset and it measured infinity at .75 offset. I had been thinking the thing through and figured I would try to make it "sense" off idle throttle position with greater sensitivity. I wanted it to immediatly show off idle throttle by getting the .5 mm resistance measurement as close to the infinity trip point as I could.

I got it to 175 Ohms, anything more and it would trip over to infinite resistance or one of the other two measurements would be out. After that, no issues, it seems to have taken care of the problem.

But, your issue could be caused by any of the reasons already suggested.

Good luck.

Mike