90 max 2.4 idle/ run issues

[yosemite]

I have a 1990 Mighty Max 2.4, starts fine, when warm it's Idle pulsates or "hunts" a few cycles then goes to fast Idle, and most recently I set out from the house , started down the access ramp, and itstalled, or nearly, as if someone were turning the ign off and on, now it is pretty much a lawn ornament, have driven a few times since, still pulsates, but afraid to go far, my initial thoughts were te IAC, but that was berore the off on situation, any suggestions? and BTW Happy NEW Year

[4doorciv]

Happy new years and welcome to the board. My g63b would do that at a certain rpm all the time. I found out I had a small coolant leak and because of that I would get this bucking between 2.5k and 3.5k rpm oy on light throttle application. Fill up with water and I was good to go. Only a small hiccup at 3k. I would start out with the easy stuff like check all your fluids and check your ecu for anythink that looks wierd like something verry small dropped in ther and made a puddle. Then I would do rutine maintenance like cap and rotor, spark plugs, wires, fuel filter, all that good stuff. Hope this would fix things.

[yosemite]

previous to the run don't run episode, it ran good off idle, but as said when warm would pulsate at idle about 6 cycles then go to fast idle, ran fine above idle

[LSR Mike]

lots of possibilities, IAT, water temp sensor, could be a throttle position sensor also. checked for any codes?

[pennyman1]

Your ECM could also cause this issue - caps dry out on the curcuit board and cause all kinds of problems. With the age of these trucks, an ecm recap is damn near essential to have it run right.

[yosemite]

back again, replaced pump,whic was not needed, replaced relay, still no run, pulled puter and opened, never seen one so clean, no signs of cap leakage, but microntroller appears to have a small crack in top of case, not sure if the cheapie rebuild guys would consider this rebuildable, I have a chance to pick up a used 1 from a 91 mm, similarly equipped but will it work on my 90, connector is same, sensors etc on both same, wiring schematic looks same part number different inside case, some components different, are the differences due to epa regs changng year to year? will different years physically interchang and be runnable? Expiring Minds Want To Know, I know you could write a book,or several, about the things I do not know about this , if someone has , where can I get a copy???