dakotachaos

Hey everyone, I'm stumped on this one. 87 Toyota pickup 22re 5sp. Long story short the truck idles terribly UNTIL I hit the brakes. I have read about the idle being set too low, and the plugged up iac but haven't read anything that matches my symptoms. Idles cold no problem, once warmed up though it has a very rough idle unless I hit the brakes. Once brakes are touched, it runs great. Thought it might be a booster vacuum leak but the symptoms would be opposite. Any ideas?

92 Yoda

I had a similar problem, it's related to the coolant system I believe. I'd start by checking coolant level and then checking for cel codes.

dakotachaos

Coolant level is good, although I have been without heat for a while. Possibly air in the system. I'll check for cels tonight

jennygirl

Braking should not affect idle at all really. Happens when at a dead stop, too, or just during decel braking?

Definitely burp the coolant system first, which should bring your idle up to regular with no brakes. Then I would say try capping the vac line to the brake booster to see if that stops it from affecting idle (if it happens while stopped, too). If footing the brakes still has an effect on idle, it has to be electrical. If it's only when braking during decel, it could be grounds.

https://www.yotatech.com/forums/f116...-guide-194413/

But if being at speed makes no difference, maybe you are running rich due to coolant temp reading too cold from an air bubble and a brake booster diaphragm leak gets it closer to stoich?

Certainly a weird problem, hope you find it!

Edit: another thing you might want to check is AFM, you could have a compromised spring and decel braking could be moving the flapper? See if there is play in it

jennygirl

Ooh I just thought of this. In a typical properly set up motor, the engine cuts fuel during braking when above 1100 rpm. Maybe your TPS it out of adjustment, and the ECU is getting confused about where idle actually is.

What kinda rough idle, stumbly/sputtery, surging, or all of the above?

Schnayke

iTrader: (1)

Mine was idling high, and would get even higher when i applied the breaks. I replaced the vacuum hose and it fixed the problem. I also replaced the one way valve in the middle of the can line.

dakotachaos

I really appreciate all of your inputs on this! didn't have much time tonight to mess with it but eliminated some ideas. Plugged booster vac line at the manifold and it still had the same issue. So the vacuum line, check valve and booster are out. Removed the iac and it was free and clear. So next up is wiring/grounds. Thanks for the link! To give a better explanation of the symptoms, when at a stop, engine idling, with brake off it sounds/acts like there is a large load being put on the engine. Sort of like you turned all electrical acc on plus 52 off-road lights on and the alt is working extremely hard to keep up. Battery at rest and charging are close to spot on. 12.3 and 14.6v. I will be digging deeper tomorrow night and will get back to you!