high idle

I have an 89 D50 4X4 that I put a 3.0 V6 in. It runs great but when started, it idles up around 2k until it gets warm and then comes down and idles fine. However sometimes I will be driving along and it starts to idle high while it is at operating temp. Sometime it takes a while for it to idle properly. Any ideas? I replaced the temp sensor and had the computer rebuilt when I rebuilt the engine.

How about the high idle solenoid. The one that kicks up the idle for the AC. I think it makes a vacuum leek to do that. I may be wrong. The other guess would be a sticking cold start injector or something along those lines. Or the MAS is doing something strange. How is the fuel mileage since it started doing this?

It has done it from the start. After I rebuilt the engine it would rev wildly high to low until it warmed up. That is when I replaced the temp sensor. That stopped it from doing that but it has always done this other thing since. Fuel economy is a steady 19 which is acceptable but not great. Don't know what I should be getting with this engine.

I have a '90 and a '91, both 4x4's with 3.0 V6's and I'm always in the 17-20 mpg range. It doesn't seem to matter if they are running empty or hauling a ton of stone, the mileage is very consistent. My all time best was on a trip keeping it right at 60 mph and I got a whopping 21 mpg!

Thanks Guess I'm doing o.k.