in the mood for online diagnostics?

[jatibb]

ill try and keep it short. truck started running rough at idle,and almost stalling when leaving stoplight. finally popped a code 48. purchased aftermarket stepper, replaced. when cold, starts right up, when warm almost seems like its not getting fuel at start up, will fire a stumble to a halt 2-3 times then wont start. sometimes if i time a pump of gas pedal at right time it'll start but idle at 1500 rpm before settling down.but when it does finally start it runs fine until you shut it off again. again, it doesnt really have to get warm to have the same old problem. ive felt the amp on the dizzy and it is not hot or even warm sometimes. ive sprayed carb cleaner all over the intake and surrounding area hoping for vaccum leak, nuthin. so far ive purchased 2 new (aftermarket) steppers and still have the old one. it had a "made in mexico" stepper in it for the last 2.5 yrs ive owned it so i dont think it'd be a problem with aftermarket parts. the tips all look the same size.a couple of possible hints.. when setting base idle per online instructions when i start with the stepper disconnected it wont come below 2000 rpm no matter what, another, when i disconnect the bypass hose in the back of plenum there is suction on both ends (hose leading to plenum and stepper housing. anybody got any ideas, i dont think its fuel related because it runs fine, when it runs at any speed and ive replaced the fuel pump off the parts truck trying to figure this out. oh yeah, 1991 rr classci 3.9

 

[muskyman]

did you just replace the stepper or did you also clean the inside of the stepper housing?

a tooth brush and some diesel kleen will clean it up real well and fix alot of idle related issues.

 

[greenmeanie]

Out of left field perhaps because I have no idea what a code 48 is on one of the modern fagled computerized thingies but it could be a coolant temp sensor gone south. If the computer is getting a false reading thinking the engine is cold it will richen the mixture - I think some run open loop at that point. If the engine is cold it will start on this rich mixture but if hot it will essentially be flooding the engine.

Temp sensors are cheap to reaplce so worth a shot.

 

[evilfij]

Bad something else in the system. Probably 02 sensor, but possible coolant temp or MAF.