medicman

I'm having a problem on my 91 toyota pickup thats absolutely driving m crazy. When I start it up cold it seems to idle fine until the engine warms up and then the idle increases, and everytime I apply the brake it starts surging.I changed the master cylinder, new air filter, plugs, wires, and set the timing still does it. I thought the other day it was fixed cause I was looking around under the hood to try and see if i could come up with a solution and I removed the vacumn hose from the brake booster and it seem to quit. Now I dont know if this is a coincidence or what but it didn't do it any more for about three days and I thought it was fixed. Last night I was coming home around 9Oclock and as I came up to a stop sighn and applied the brakes it started the surging again. Anyway I'm a little lost at this point. the engine ecu does throw up two codes one is a 31 and 34. I dont know if this would be any relation to the problem or not. It seems that this problem is very common amongst these engines anyway any help would be greatly appreciated. I plan on changing the coolant temp sensor and cleaning the throttle body this weekend too.

j2the-e

Did you try adjusting the idle screw? Did you check the oring on the idle screw? Did you bleed the cooling system? Did you check for vacuum leaks? IAC valve?

medicman

No sir I havn't just trying to get some ideas cause I have seen several posts of this same problem with a whole lot of suggestions so I guess I need to start there. How do I bleed the coolant system? and set the idle thanks.

GrandPrix

medicman,
Not to enflame or offend, but this topic has come up a million times and everybody has a possible solution that never seems to work. I had/have the same problem with my 92 22re and have tried everything advised here to no avail. The problem goes away and comes back when it wants. No reason. I have given up. As long as the engine runs, I don't care anymore. My advice is to ignore it. Or you can make yourself crazy trying to chase ghosts.

j2the-e

Run the engine at 1500 rpm with the heater on high while periodically squeezing the upper hose. 5-10 minutes. A spill-proof funnel makes it much easier.
To set the idle, turn the adjusting screw on the top of the throttle body. The adjuster screw has an oring on it that can become brittle or hard and either leak or allow the screw to back out on its own from engine vibrations.

Assuming no vacuum leaks, I would bleed the cooling system first. Then check the idle speed. If you still have issues afterward, IAC valve is suspect.

Murcielago

With all due respect to the other commenters, air in your cooling system shouldn't cause this problem, assuming there's enough water to maintain the engine at the proper running temperature.

However, a vacuum leak could well cause the problem. If you get a vacuum leak, what you essentially get is a rush of additional air into the engine. This causes it to speed up, though it'll be running lean as that air won't have passed the airflow meter, which controls the amount of gas.

There are about couple dozen vacuum hoses running to various parts of that engine. One (rather crude) way to diagnose a faulty hose is to start the truck, get it to full operating temperature, then pull off the vacuum hoses, one by one. After each hose is pulled off, note if the engine runs any differently. Then put it back before you go to the next hose. If you get to a hose that doesn't affect how the engine runs, make a note of it. After you have done that to all the hoses, you should have some clue as to which ones could be related to the problem. Then you can either investigate what systems the problem hoses are connected to, or carefully examine each such hose for leaks/cracks/etc. BE VERY CAREFUL TO NOT MIX UP THE HOSES.

Aside from the power assist booster (which could have a leak; it's powered by the engine's vacuum), nothing else in the braking system should cause this problem, so stop worrying about bleeding, master cylinder, etc.

j2the-e

With all due respect of course, I have seen this before, multiple times. The issue is that the upper hose is bent in such a way that a small air pocket can sit in the tstat housing. This can cause the coolant temp sensor in the tstat housing to get an improper reading. A cooler temp sensor coupled with a hot IAC valve can cause some weird things. While we're on the subject, a coolant blockage at the IAC valve can cause some issues too, though I've never seen it cause a surge. Just speaking from my own experience. Not a difficult check to do.

Murcielago

Well, thanks! I learned something from your post. But to me, it still seems likelier to be a vacuum issue.

j2the-e

We shall wait and see.............

Tbrown0102

Good luck!