So this has happened very rarely, maybe 3 times in the past 2 or 3 months. When I startup my truck for maybe 5 or 10 seconds the idle will steadily fluctuate between maybe 900 and really low like 300 then go back to normal. What do you guys think? I'm not to concerned about it since it is such a rare occurrence but I am curies.

My 99 Trooper did that same surging thing...turned out to be the intake manifold gasket. Pretty common problem...

LOL just replaced that 2000 miles ago.

Well FWIW the IMG went out TWICE on my 99 Trooper... <img src="/forums/images/graemlins/shiner.gif" alt="" />

Mine also did that before the IMG went last winter. The dealer told me that they usually go when there are big fluctuations in ambient temp (I don't know if you have that in Sunny CA).

My new IMG has lasted about one year and 20K miles and so far so good.

I have a 99 Rodeo with 126000km. Mine has been doing the "Idle Surge" for about a year and half. It runs great other than that. I have replaced the IMG as well. It started surging along with some other problems so i had it replaced and it still surged. Im out of ideas and the dealership has no idea without me spending a pile of money for them to try and find the problem. There advise was if it runs good. Live with it.

an O2 sensor maybe? Mine is doing it now and that is the first thing I thought of.

How big of a job is it to replace that IMG?

Replaced all the O2 sensors maybe 500 miles ago.

Haven't had it fluctuate since I started this thread, it's just so random and rare, probably some wire somewhere.

IMG isn't to bad to do, but it depends if you just lift up the manifold or actually remove it. I like the idea of actually removing it so you can really clean it and clean up the gasket surfaces, also with it removed you can change the thermostat. But it can be difficult to get the bolts for the fuel lines off the back of the manifold and changing the thermostat requires a universal joint 12mm socket, not a 12mm with a universal added to it. Also other things here and there, I could tell people if they really wanted to know.

My engine was surging until it finally threw a code for the EGR valve. I cleaned the valve and no more surging. It may not be what's causing trouble for everyone but it's easy and quick to clean the EGR valve.

Did that too when I changed the IMG.