1987 suburban 454 T.B.I. Issue

[Chrisg82]

My 87’ suburban 28,000 miles recent full tune up ,fuel pump ,fuel filter .cold start usually high idle for a minute or so ,then kicks down .right around 950-1000 rpm when warm .never skipped a beat or sputters.went for a drive yesterday ,usual behavior.came to a light ,started rough idle like she was going to stall out ,once back in the gas seemed to clear up .was fine for a few minutes ,then started again ..and won’t clear up .now getting into the throttle ,started to buck and pop (backfire) out of the throttle body ....never had an issue with the truck in the year I’ve owned it ...any info or a place to start would be greatly appreciated .common issue ??

Thanks Chris

 

[89 GMC Burb]

I would check the vacuum hoses. Sounds like it has a leak somewhere or the timing jumped.

 

[1987 GMC Jimmy]

Is the SES light coming on at any point during this? Does it come on when you first turn the key on? If it’s actually idling like that, that’s a bit high first of all. You can try an IACV relearn which involves jumping your A/B pins (top right two pins, paperclip works best) on the ALDL, turning the key to ON for thirty seconds, unplugging the IACV connector, turning the key off, removing the jumper from the ALDL, and reconnecting the valve plug. If that doesn’t solve your idle speed, I’d consider replacing the valve and performing the aforementioned procedure. I’d like to see what your vacuum is also, but do a thorough check for leaks including at the base gasket and brake booster. I had this issue when I first got my car, and it ended up being a fried ECM that had gotten wet when it rained.

 

[Chrisg82]

I do not have that light on my dash ,lights come on with ignition power but go out .no lights on the dash when this is happening

 

[4WDKC]

borrow a fuel pressure tester from the parts store and check while running.

 

[Chrisg82]

Thanks for all the help ,turned out to be the ignition coil .