Well, I've tried searching this and other forums/sites, but I can't seem to get enough info to figure this problem out. 1990 4runner V6 3.0 4x4: I have an Idle with a mind of it's own! At any random time, it will drop from about 900-800 to about 500...(it kinda jumps/hops around 500 like its bogging down and gonna shut-off but never does.) Sometimes when Im driving, it idles perfectly at 800rpm or a little lower. At night, the lights get dimmer till I start driving again. I've replaced the fuel filter, used SeaFoam and various other injector cleaners. I haven't touched the Idel screw yet, because Im curious as to why it idles at normal speed sometimes. Could this be "Air/Fuel" related or is it just something bizarre? I've only had the truck a year and haven't messed with anything electrical except a new battery. I am going to replace the spark plugs soon, regardless if that is the problem or not. If anyone has anything else that they think I could check, It would be much appreciated. Thanks in advance.

 

I'm no 3.0 expert, but 3 things come to mind right away...

temp sender (for the ECU), TPS, and AFM...

if you've got a multimeter, their easy to OHM out and test; just look up the correct numbers in the FSM sticky

 

EGR valve?

 

i have a 90 with a v-6 . it doe's the same thing it idles hi after it gets warm. you hit the brake and it goes up and down but if you have it in 4-wheel drive it idles fine..

 

Do you have a vacuum actuated front diff? This sounds like a vac issue to me.

 

My first thought when reading the post was a vac leak....may want to spray some carb cleaner around the hoses while the truck is running to see if it idles up after the hoses are sprayed.

 

Idle Surge......this could be a number of things that will drive you crazy. I suggest troubleshooting the cheapest and easiest items first.

1. Check for a Vacum leak. Look at all the vacum hoses and if it looks like they need to be replace.....change them out. You buy several feet of these hoses for cheap. (There are different ways to test them out, the eyeball test worked for me......found 2 torn up hoses at the back of the engine that I would have never thought of looking.)

2. Change out your PCV valve. This can be a little tricky on the 3.0 but it can be done with some needle nose pliers and some skill. Trying searching for this on the forum, it should be somewhere. The PCV cost under $10 at your local Toyota Store.

3. Adjust your idle to make sure it is at Toyota Recommendations (VECI label under the hood). This is fairly easy and you can always decrease or increase. There are other ways to try and get this right (using a hand-held tachometer), but I gave it the ear test.

All of these combined solved my problem of random idle surge and were fairly cheap troubleshoots. My idle would drop below 800 rpm then surge all the way up to 2500 rpm and then bounce up and down. It was really random, now it idles they way it should.

Hope these work out for you!

John

 

Hey, i am having a similar problem with my '89 22re. i adjusted the idle to about 1,500 (i know, high) but that seemed to solve it untill it started being jumpy with the idle. taking it down my hill, it would stall out on curves (not good for a colorado switchback road). i put a full tank in it (the tank was about 1/8th full at the time) and that seemed to solve it untill, yet again, it does it.

when the engine stalls, it goes from about 1200 RPM to 500, then down to 200, then stall, but sometimes it would bounce back from the 200. when the ride was bumpy (going on a flat road at this point) the engine would jump from 2500 to 3000, to 1200, all while in H2, 2nd gear, going about 30MPH.

any suggestions?

 

I had a problem with my idle too high. When i pressed on the brake the idle would drop to 1k and bounce up / down. The injectors cut out when breaking to assist stopping. Thats why it bounced down for me. I ahd to lower the idle using the idle screw, this solved my problem. I first tried setting the tps but it caused my idle to bounce up and down like you said, so adjust your tps 1st, (after idle adjustment) if that doesnt work look for a vakuum leak with some starter fluid. I think its ur tps tho.
Heres the link to set it:. http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml
Good luck!

 

Vacuum leak.

Mine did the same thing. I also had a fuel leak though.

 

alright, thanks man. i'll chek that out this afternoon and let ya know.

 

alright, well i checked out my tps, and it checked out with ohms and all as the repair manual says so, so there shouldnt be anything wrong with that, right? second thing i did was lower my idle speed. its at a solid 750 now, and i let it idle for an hour or so with no issues, drove it down to napa, no issues, so its running fine now. but i'll keep that link in mind if it acts up again. thanks!