I cant figure out whats wrong with my 89 v6 truck. Upon initial startup it runs great, idles fine. You can drive it for about 3-4 minutes and it will be great. After it warms up, it has an idle problem. When the brake is depressed at a stop, the idle surges up and down, its pretty rough when it does it. If you lift your foot off the brake it idles smooth. Ive disconnected almost every vac. line one at a time, and plugged them to see if there would be any change and there isnt. The pcv valve seems free, not frozen. Only when I pull the breather hose that goes to the air intake tube does the idle seem to slightly straighten out. Any ideas?

 

Might want to check out your DASHPOT. also, is it a 3.0?

 

Once i idled my mine down it stoped doing it....I don't know the precise idle speed for it. but i turned mine down to about 8 on the tach and it stoped doing it

 

Turn the idle speed down:
- http://www.4crawler.com/4x4/TLCA_Tru...ech.04.09.html

 

Most idle surge problems are due to vacuum leaks. Try clamping of disconnecting your brake booster vacuum line and see if the problem is the same. You may have a booster with a leaking diaphragm.

 

I had a similar problem with my '94 22RE. Check out this thread:
https://www.yotatech.com/forums/f116/up-down-idle-100465/

 

this does it all the time after warmup, it never goes away. If I put it in 4x4hi it goes away, when its put back in 2wd it comes right back. I can only see a small stud with a nut on it to adjust the idle and it looks like its almost all the way down, almost 1 thread left if that. I cant find the idle screw.

 

when mine surged all the time, it ended up being the timing belt. it broke when i was interstate traveling, talk about suck!.

it didnt last long from the day it started surging until it finally broke...matter of weeks.

just maybe something else to take into consideration.

 

Idle screw is usually a large headed screw on the throttle body.

 

I know where the idle screw should be, just didnt see it anywhere, all I see to adjust it were the nuts and studs, any pics from the v6?

 

I snipped the green/white wire at the ecu and all is well

 

same happened to mine,ended up overheating and blowing a head gasket

 

Using info gained at 4crawlers page, I also snipped the wire at the ECU and now when my idle wanders up a little too high I get no fluctuating idle at all.

I made a thread about it with pics showing the exact wire.

Search for fluctuating idle and you'll find it.