truck idles down till off

[Nathan N.]

When I start my truck it starts fine but after about 3 second it idles down s
lowly until its off. When I unplug the iac the rpms increase really high gradually then I plug it back in it again slowly decreases till its off. Any help would be appreciated.

Topic

[college man]

Try tapping on the IAC with the handle of a screw driver to see
if the idle changes.If it does change the IAC. also turn on the
ac to see if the engine idles up.if not change the IAC.Whats
the make,model,year and engine size of the truck? how many miles?

[Nathan N.]

93 s10 blazer 4.3 fi 140xxx miles. I switched out the iac with a new one and nothing changed.

[college man]

are the passages clean? also search for vacuum leaks.

[Nathan N.]

All the passages are clear and its hard to keep running but I sprayed carb cleaner and when I got to the air intake it shut off quick. So would you think it could come from my plastic intake being dry rotted? if it is wouldn’t it run at higher rpm’s?

[college man]

If the air intake tube is dry rotted and the truck shuts off.
Then thats a major vacuum leak. The truck shuts off due to unmetered
air.Try pulling the vacuum booster line off and see what happens.
you need to replace the air intake tube to stop the vacuum leak.

[Nathan N.]

I unplugged the brake booster and it stayed running. I had tapped up the intake hose and it still shuts off? It also runs real rough when I give it a little gas then smooths out when I give it
allot

[EricTheCarGuy]

That does sound like it might be a vacuum leak. It’s worth checking anyway. GM’s are famous for intake gasket leaks. You can use the info in the video above for that. Also, do you have any check engine lights on? If so start with those as they are an important clue to problems like this.

Keep us posted on what you find.

[Author]

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