Have any of you ever hard of a truck's idle surging when the brake is applied?? Mine does it only when the A/C is on. My friend's truck does it also, and he has no A/C. Both are 4x4.

 

idle set to high ?

 

Idling mine down to just under a grand fixed it

 

2 possible ideas- on the AC equipped vehicle, there is an idle-up solenoid the bumps the idle up to compensate for the increased load of the compressor.
If the idle is set too high already (up at 1000rpm-ish) the bump-up from the solenoid will push the idle up high enough that the computer gets confused and tries to lower the idle. That's when the idle bounces up and down, as the two things fight each other for control of the idle.
This is also complicated by the brake circuit. The computer assumes if the brakes are being pressed (it sees voltage in the brake light circuit), then it should be at idle. If the idle is set too high, the computer tries to force the idle down. You then get the same bouncing idle, as it fights itself for control of the idle.

Good luck!

B

 

where is the idle up solenoid?

mine is surging to i replaced the thermostat and plugs last time it started doing this and it fixed it .

it just started doing it again recently so i figured it was a bad thermostat so i replaced it (again) and flushed the radiator but that dosent seem to be working this time .

any ideas ?

edit*

i have the 91 yota 22re pickup 4x4

 

OK so I just bought my 94 2wd for $300... when I give it a little gas and it gets to a certain rpm it has a surge to it but it doesnt do it at idle...I had another 94 a few years back and it had a surge at idle. This truck didnt have any coolant in it at the time and im wondering if that has to do with the surge? I filled it with water today so I can run it for a while to flush it out and it still has the surge, it gets really annoying when im driving when it drops rpms then they raise back up really fast, Ive heard the problem could be the tps too but I dont think its that but I could be wrong... Anyone know what it could be please help?????

 

Sounds to me like the Igniter box.

 

X3 on the idle speed. Why, see the 2nd Q&A below:
- http://www.4crawler.com/4x4/TLCA_Tru...ech.04.09.html

 

There is a thread somewhere on here that has got a lot of good ideas on idle issues...you should search for it, it helps. Other options for surging is a plugged up auxiliary air valve or also named the idle air control valve (on the bottom side of the throttle body on my truck) or you could be low on coolant or have an air bubble trapped somewhere in your coolant system. Just some thoughts...