high idle - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jaspadafore · 09-17-2004, 04:22 PM

I have a 89 gmc 1500 pickup with tbi.....my idle is to high and i dont know what to do...it's real high in park and then drops when i put it in gear, but even in gear its real high....what can i do.....

ChevyTech · 09-17-2004, 04:35 PM

A vacuum leak can make it idle high. The base gasket under the TBI unit tends to fail a lot. Check your vacuum hoses and PCV hose and valve.

Your IAC (Idle air control) valve could be stuck with the plunger retracted.

A bad coolant sensor can make the computer think the engine is cold causing a high idle. Does it seem to run to rich?

Is there any other symptoms other then the high idle?

MD8349 · 09-18-2004, 07:52 AM

ChevyTech WHERE IS THE COOLANT SENSOR USUALLY LOCATED.

ChevyTech · 09-18-2004, 09:36 PM

On a TBI V8 chev it is screwed into the intake manifold just to the passenger side and forward of the thermostat housing. This is the coolant sensor for the computer only.

The coolant sensor for the dash gauge or light is in the cylinder head in the area kinda between the spark plugs.

Arrow211 · 11-30-2004, 08:19 PM

Also you may have to reset IAC motor settings, (curb idle).
If someones played with the factory settings.supposed to be around 500-550 rpm, with iac disconnected & aldl jumped.
Lots of instructions online as to how to properly rest factory curb idle speed.
BTW: That idle speed effects almost ALL your computer sensors as to what they read.So mileage & power will suffer GREATLY.

greg0380 · 12-01-2004, 11:56 AM

Don't mean to hijack threads, but I have been tracing a high idle issue for a while and really havent gotten too far. I'm pretty sure its not a vac leak but since you guys were talking t-stats, I was wondering if that could be my problem. I have noticed the truck smells rich and with WINALDL the temp. sensor shows a consistent 188-189 degs once it warms up. Is that too low? The stat is rated at 195.

Arrow211 · 12-01-2004, 12:06 PM

I agree with chevy tech:
If it was mine I'd go after the thermostat first , till I got one reading at 195 degrees, my sons 4x4 (91) read 188 on an aldl reader we swapped out 3 thermostsats (gm's) until we finally got a 195 reading & changed the comp sensor unit, he improved by 6 mpg, these engines really are VERY temperature sensative.When that comp wants 192-195 it really does mean it.His was running so rich and at $4.00 a gallon it was costing.good luck.

greg0380 · 12-01-2004, 01:23 PM

I looked at a recent WINALDL that I had logged and the highest temp read I got was 190, I will change the tstat. thanks for the input...

Arrow211 · 12-01-2004, 01:48 PM

If it is a vacuum leak,fel pro tbi base gasket actually seals better than the stock gm gasket.been there , done that.
Firstly, check in drive to see if engine is "hunting" at idle.
If the comp cannot find the perfect idle, it most likely a vacuum leak.
vacuum hoses, tbi base gasket,intake leak,power brake booster,even a sticky egr valve.
a malfunctioning idle air control motor, will cause high idle,a thermostat, temp sening unit (computer one)chevy tech talks about.
warning, use gm coolant computer temp sensor, or standard motor products brands only.
I've got a box of other brands that DO NOT work properly !
For Iac motors use gm only.

09-17-2004, 04:22 PM	#1
jaspadafore Registered User Join Date: Sep 2004 Posts: 3	high idle I have a 89 gmc 1500 pickup with tbi.....my idle is to high and i dont know what to do...it's real high in park and then drops when i put it in gear, but even in gear its real high....what can i do.....

12-01-2004, 11:56 AM	#6
greg0380 Registered User Join Date: Dec 2003 Location: CT Posts: 454	Don't mean to hijack threads, but I have been tracing a high idle issue for a while and really havent gotten too far. I'm pretty sure its not a vac leak but since you guys were talking t-stats, I was wondering if that could be my problem. I have noticed the truck smells rich and with WINALDL the temp. sensor shows a consistent 188-189 degs once it warms up. Is that too low? The stat is rated at 195. __________________ 1985 GMC Sierra 1500, 1/2 ton, 2WD, LWB, TBI 305 5 speed, 3.42 rear 2007 GMC Sierra 1500, xtended cab, 4X4, flexfuel 5.3L 1999 BMW 528i

12-01-2004, 01:23 PM	#8
greg0380 Registered User Join Date: Dec 2003 Location: CT Posts: 454	I looked at a recent WINALDL that I had logged and the highest temp read I got was 190, I will change the tstat. thanks for the input... __________________ 1985 GMC Sierra 1500, 1/2 ton, 2WD, LWB, TBI 305 5 speed, 3.42 rear 2007 GMC Sierra 1500, xtended cab, 4X4, flexfuel 5.3L 1999 BMW 528i

09-17-2004, 04:35 PM	#2
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	A vacuum leak can make it idle high. The base gasket under the TBI unit tends to fail a lot. Check your vacuum hoses and PCV hose and valve. Your IAC (Idle air control) valve could be stuck with the plunger retracted. A bad coolant sensor can make the computer think the engine is cold causing a high idle. Does it seem to run to rich? Is there any other symptoms other then the high idle?

09-18-2004, 07:52 AM	#3
MD8349 1999 Chevy Join Date: May 2004 Location: DALLAS, TX Posts: 61	ChevyTech WHERE IS THE COOLANT SENSOR USUALLY LOCATED.

09-18-2004, 09:36 PM	#4
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	On a TBI V8 chev it is screwed into the intake manifold just to the passenger side and forward of the thermostat housing. This is the coolant sensor for the computer only. The coolant sensor for the dash gauge or light is in the cylinder head in the area kinda between the spark plugs.

11-30-2004, 08:19 PM	#5
Arrow211 Registered User Join Date: Nov 2004 Posts: 45	Also you may have to reset IAC motor settings, (curb idle). If someones played with the factory settings.supposed to be around 500-550 rpm, with iac disconnected & aldl jumped. Lots of instructions online as to how to properly rest factory curb idle speed. BTW: That idle speed effects almost ALL your computer sensors as to what they read.So mileage & power will suffer GREATLY.

12-01-2004, 12:06 PM	#7
Arrow211 Registered User Join Date: Nov 2004 Posts: 45	I agree with chevy tech: If it was mine I'd go after the thermostat first , till I got one reading at 195 degrees, my sons 4x4 (91) read 188 on an aldl reader we swapped out 3 thermostsats (gm's) until we finally got a 195 reading & changed the comp sensor unit, he improved by 6 mpg, these engines really are VERY temperature sensative.When that comp wants 192-195 it really does mean it.His was running so rich and at $4.00 a gallon it was costing.good luck.

12-01-2004, 01:48 PM	#9
Arrow211 Registered User Join Date: Nov 2004 Posts: 45	If it is a vacuum leak,fel pro tbi base gasket actually seals better than the stock gm gasket.been there , done that. Firstly, check in drive to see if engine is "hunting" at idle. If the comp cannot find the perfect idle, it most likely a vacuum leak. vacuum hoses, tbi base gasket,intake leak,power brake booster,even a sticky egr valve. a malfunctioning idle air control motor, will cause high idle,a thermostat, temp sening unit (computer one)chevy tech talks about. warning, use gm coolant computer temp sensor, or standard motor products brands only. I've got a box of other brands that DO NOT work properly ! For Iac motors use gm only.



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