I have a '88 3S-FE, it will surge from 1-2 thousand rpm. When I'm idling, usually more when it is cold out and when I have my foot on the brake pedal. As far as I know the idle isn't adjustable on this engine, correct?
try cleaning the throttle body or check the Air Intake Control valve. I had the same problem, I replaced the ECU and cleaned the TB and it doesn't do it hardly as much, plus my TB could be A LOT cleaner as well.
and scroll to page 108 of the pdf file. That's the stuff regarding the TPS, butterfly, etc.
First, I would examine the air duct from the filter box to the throttle body. Look for cracks or any place that air can get in without passing through the air meter. That's why such a leak is called "unmetered air."
Check all of the vacuum hoses for looseness or leaks.
Air getting in where it isn't expected makes it difficult for the ecm to control the idle. A good cleaning all around the throttle is always a good idea. Use throttle body cleaner spray.
Since it is affected by the brake pedal, i have a thought that maybe the brake power booster vacuum hose (or the booster itself) is cracked or broken.
My mom's old Chrysler Lebaron had a similar problem and it turned out the diaphragm inside the power brake booster was bad and the booster had to be changed. And this fixed the problem-
A ruptured diaphragm in the power booster would constitute a vacuum leak when calling for boost. You can make the booster part of your search by pinching off the hose going to the booster and observing if this prevents the surging.
Even if you're not getting a "check engine" light, use a paper clip to bridge the two appropriate terminals in the diagnostic pack; I got a smaller idle surge (only about 200rpm variance) and it turned-out to be my O2 sensor--even though I hadn't seen a warning light, the trouble code still came up. You just never know, I guess.
Mine does the same thing except it does it when it's cool outside.Pushing the brake pedal causes the surge even more. I plugged off the hose and it still does it. When ambient temp is in the 80's it runs fine.
The brake booster is helped by using vaccum to apply the brakes. So when you press the brakes it affect the "whole" vaccum of the engine. So if there is vaccum leak, or something isn't working right, this little bit of chance in the system can have a real affect.
That would be true EXCEPT I disconnected the hose from the booster(covered the hose with my thumb) and had my wife push on the brake and it did the same thing with no hose connected. Here's another clue: When the ambient outside is cold-say 70 degrees or less, this condition occurs. when the ambient is in the 80's or more, there is no more surge. Wierd huh?