I have a 1991 2.3L 4 banger, manual transmission that I acquired from my father. Truck has always idled high - 1200 to 1400 rpm - but has lately taken to racing to 2500+ rpm at start and slowly settling back to the "normal" 1200 or so idle - and by slowly I mean over a period of minutes. I have pulled the idle stabilization valve, cleaned it and confirmed it moves freely. checked the vacuum line to it and and checked the electrical connections.Is there anything else that would affect the idle on this engine that I should look into? Is it time for a new idle stabilizing valve? Truck has approximately 120,000 miles on it.

Jeff

 

Welcome to FTE.

Your problem sounds quite similar to mine. When I have asked for ideas, the response has always been: "You have a vacuum leak somewhere." That may be true but I have looked, poked, pulled, pushed and tried all sorts of ways to determine where the leak is. I have yet to find it on my truck.

In spite of that, I would encourage you to check vacuum hoses for possible leaks - there aren't that many hoses to check and try a propane test. To do that, move the truck outside, start the engine, let it warm up, then use an unlit propane torch to "spray" propane over the engine intake system. If the idle speed picks up while you do this, you have found the source of the leak.

Good luck.

 

Thanks for the suggestion - I'll take another pass at it. I have checked vacuum lines, but found nothing. I do know how hard it can be to find a small leak, so I guess it's worth another look if that is the colective wisdom of the group.

 

a bad PCV valve will cause a high idle, and not throw a code.
worth checking.

 

Oh boy - the PCV valve! Oh well, another thing for me to play with!

Seriously, I appreciate the input - it is something I should check due to the age of the truck, but did not realize it could affect the idle speed. Thanks for the suggestion.

Jeff

 

x2 on vacuum leak

 

I don't know what an 'idle stabilization valve' is. My old truck has an IAC, Idle Air Control, that adjusts the idle speed. They can get gummed up. A delayed return to a lower idle speed is indicative of a gummy IAC, IMO.
I have also heard of leaks in the large air tube between the air cleaner housing and the throttle body. Some have a ribbed section to allow for flexibility and engine movement, and they develop cracks between the ribs.
If the idle stop screw has been adjusted too high, you will get a high idle as you report. Check the spec on the decal or the shop manual, and turn the screw counter-clockwise a little bit, and then open the throttle and let it go closed, and then check the rpm. Repeat as necessary. My 2.3 idles at about 700-750rpm.
tom

 

Again, thanks for the input. I won't get a chance to work on the truck till the weekend but I will check both of these possibilities.

Thanks for your input - I know it has to be something relatively simple that I have overlooked.

Jeff

 

I have had more than one of these engines that have had bad manifold gaskets usually but not always on number 4 clyinder. Caused by a warped manifold. Get the wd-40 or carb cleaner out and start spraying stuff down you will know when you find the problem. And yes I have had PVC valves do this also.