I've recently noticed that after a short trip with a warm engine; I get a bucking inconsistent idle upon warms start-ups. The engine revs up to 2000 rpm and down to about 500 and back up for about 30 seconds, then smooths out.

Previous experience points me at fuel pressure, but the truck drives fine. Its only idle at initial start-up on a warm engine.

Im confused here need some help.

 

So am I.

What engine are we talking about?

 

vaccuum leak?

 

This is a 22re with a 124000 miles on it.

 

Are you doing anything when the idle is bouncing up and down, like on the brakes? If might be the idle is a little too high and you are hitting the ECU idle cutout RPM. It cuts fuel if it sees the idle speed too high. Or you might have an air bubble in the cooling system. If that bubble gets under the ECU coolant temp sender, it can send erroneous readings to the ECU and it'll switch between fast-idle and normal-idle.

 

I cant really say. I wasnt paying attention when it has happened. I'll try to induce it and observe.

 

Seems to me like 9 times out of 10 the 22re surging idle problem is simply due the idle being set too high. As 4Crawler said, if you're on the brake, the ecu will cut fuel after a certain rpm, i believe it's 1200 or so. Then the rpms get low enough for the fuel to be turned back on, then rev too high and get cut off, then down low again, etc, etc. Sometimes the idle will be set high to mask other problems, like vacuum leaks. Your throttle position sensor might be out of adjustment as well. Another thing i've noticed on other's trucks, is that sometimes the dashpot on the throttle body won't close fully. If you look at the side of the throttle body, there's a little saucer shaped thing underneath that has a little rod on it that goes in slowly when you close the throttle and basically acts as a shock absorber for the throttle. These things sometimes get dirty and don't let the throttle close all the way.