brycetryce

Hey guys, got another 3vze with an idle issue. Basically, idles high on initial startup, after about 10min and the engine is warm the idle drops to where it should be. HOWEVER, after driving the car for a period of time, the idle shoots back up and surges when I press the brake pedal. The high idle issue remains until the car is cool again. This happens every time i drive the truck.

Ive replaced and adjusted the tps about 1000 times.
Cleaned TB (not sure if coolant valve is working properly but it doesn't seem to be sticking.)
EGR working
Timing at 10 degress
idle speed screw is all the way in.

MudHippy

Idle screw all the way in means you probably have an unmetered air leak at and/or before the screw. Change the o-ring on it, and/or find the leak in the air intake tube(s).

If that doesn't work you have a vacuum leak somewhere after the throttle body.

brycetryce

Thanks for the reply. I will take a look tomorrow. I should mention that there have been a couple instances where I have had to back out the idle speed screw because the idle had dropped too low after the initial warm up. But after driving and the idle rpm increasing, I had screw it back in.

brycetryce

So as it turns out it was a bad/sticking coolant valve (the thing thats built into the tb). I put a piece of tape over the coolant valve air port before the butterfly on the tb and started the car, perfect idle. So my next question, is it possible to remove and replace the coolant valve or do I have to go buy a new throttle body. If "coolant valve" isn't proper terminology I apologize and welcome someone to correct me haha.

MudHippy

It's called an Idle Speed Control Valve(ISCV). Unfortunately no. You can't replace it, as parts for it are not available. You'll probably have an equally hard time finding a replacement throttle body too. That is if you want a new one. If you want another used one, they're a bit easier to find(http://car-part.com/).

But you might be able to fix the one you have. I've heard of others fixing theirs by cleaning out the crud causing them to stick. There's no instructions on the procedure. But it just takes a little common sense to figure out how to go about it. Compressed air blown in one side of the coolant passages seems to work sometimes. But you can also disassemble the valve if you have to. Getting it put back together and adjusted properly might be a bit tricky. But not impossible.

More info on their(wax type) construction and troubleshooting found in the link below.
https://web.archive.org/web/20141220.../forms/h21.pdf

brycetryce

Thanks for that diagram mudhuppy, made the process a lot easier. I was able to fix the problem by cleaning and adjusting the cold air bypass valve. It looks like the threaded ring wasn't seated far enough in for the valve piston to contact and make a seal when the wax plug heated and expanded. I calibrated by submerging in very hot water until the wax plug expanded and I seated the ring until no water could pass between the ring and the top of the valve piston. Then I submerged in cool water to make sure that when the wax was cold and contracted, water could pass through the valve head and the ring freely.