Why does my truck die when stopped or in park every time?

Asked by Jul 26, 2016 at 09:25 PM about the 1993 GMC Sierra 1500 C1500 SLE Standard Cab SB

Question type: Maintenance & Repair

My truck's rpm is acting up, the idle is
rough, the air intake valve has been
replaced with a new one from the
factory, the throttle body has been
checked gasket replaced, spark plugs
are brand new ac delco's, fuel is
coming through the lines, truck is
acting as if I was driving a stick shift
and dies without putting my foot in the
clutch. Oil is good, battery is at 15, 3
different mechanics have looked at it
and can't seem to pin point it. Please
help.

1 Answer

After replacing the Erg valve, the ignition module, the air intake valve, map sensor, all new AC Delco spark pkugs, doing a fuel pressure test, blowing out any gunk stuck in my lines, and cleaning out the trottle body; I took a break on Saturday and read two books front to back on how to read schematic diagrams and how horse powered engines work. I was tired of reading about what everyone else did or thought and just focused on my specific issues. My truck starts fine. As soon as I would take off the the rpm needle went mad. My temperature gauge always read at 210 during the day and these last 24 days it has been reading a quarter of that but running hot. When doing 75-80mph in 85+ degree heat I would drive it in overdrive. When in reg drive the rpm was red lining in the 4-5 zone and felt like it was hesitating on shifting when acclerating. I am starting to rule out short and think temperatur , probably my thermostat or water pump. Thermos can shut circuitry off to protect the engine and totally bypass the ecm to read normal. When stopped at a light when in drive it would do 2-4 little rumbles then choke and die. If in park it would last a little longer but still idle'n rough and die. It would start up again but super irritating and just impossible to deal with if stuck in bumper to bumper traffic. If I put it in neutral it wouldn't die. We ran several tests, my diagnostic check just blinks reg 12 over and over again. So I get my friend in my truck we take it for a spin he says pull over and pulls the coolant sensor. The small black snap in one in the front of the carburator behind the belts. Engine like on but runs perfect now! So all I need is a new coolant sensor.

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