fast idle in my DD - Pirate4x4.Com : 4x4 and Off-Road Forum

Andy351 · 08-31-2006, 08:22 PM

so my 89 k2500 (200k on original 350/700r4) has got a real fast idle and gets bad mileage. i rebuilt the throttle body and changed the idle air control valve, which helped performance quite a bit (does peg leg burnouts again

) but it still idles real high and sucks gas. when the truck is cold it idles fairly low but once up to operating temp it gets real high, the truck has no tach but my guess would be 1500-1750 in neutral. i'm not too familiar with the TBI system and how it computes, but is there something like a coolant temp sensor that tells the computer how much fuel to give? is it as simple as disconnecting the battery and letting the computer reset itself? TPS sticking?

TIA

#rawkon · 08-31-2006, 11:03 PM

Sounds like a vacuum leak, These were prone to leak around the base of the throttle body. Its a good place to start. Spray some carb cleaner around the base of the TBI while its running and listen for the idle to change

My88TexasTruck · 09-01-2006, 04:25 AM

Yes, thereis a coolant temp sensor on the engine for the ECM. I believe it is on the DS of the block between the first two cylinders. On my '88 it is a green single wire.

#rawkon · 09-01-2006, 11:34 AM

If the coolant temp sensor goes out the truck will idle fine until it warms up and then run real rich and blow black smoke. usually it dies when it is warmed up.

08-31-2006, 08:22 PM	#1 (permalink)
Andy351 Granite Guru Join Date: Aug 2003 Member # 22290 Location: San Diego Posts: 678	fast idle in my DD so my 89 k2500 (200k on original 350/700r4) has got a real fast idle and gets bad mileage. i rebuilt the throttle body and changed the idle air control valve, which helped performance quite a bit (does peg leg burnouts again ) but it still idles real high and sucks gas. when the truck is cold it idles fairly low but once up to operating temp it gets real high, the truck has no tach but my guess would be 1500-1750 in neutral. i'm not too familiar with the TBI system and how it computes, but is there something like a coolant temp sensor that tells the computer how much fuel to give? is it as simple as disconnecting the battery and letting the computer reset itself? TPS sticking? TIA __________________ www.PolyPerformance.com WE GOT WHAT YOU NEED When people in the Taliban are riding around in better trucks than you, you might have a problem.

08-31-2006, 11:03 PM	#2 (permalink)
#rawkon Registered User Join Date: Aug 2006 Member # 78077 Posts: 1,901	Sounds like a vacuum leak, These were prone to leak around the base of the throttle body. Its a good place to start. Spray some carb cleaner around the base of the TBI while its running and listen for the idle to change Last edited by #rawkon; 08-31-2006 at 11:03 PM.

09-01-2006, 04:25 AM	#3 (permalink)
My88TexasTruck Registered User Join Date: Dec 2005 Member # 64344 Location: Northern Michigan Posts: 32	Yes, thereis a coolant temp sensor on the engine for the ECM. I believe it is on the DS of the block between the first two cylinders. On my '88 it is a green single wire. __________________ 1988 Chevy Suburban 4X4 1947 Willys CJ2A Jeep

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09-01-2006, 11:34 AM	#4 (permalink)
#rawkon Registered User Join Date: Aug 2006 Member # 78077 Posts: 1,901	If the coolant temp sensor goes out the truck will idle fine until it warms up and then run real rich and blow black smoke. usually it dies when it is warmed up.