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Old 01-04-2018, 09:52 AM   #1
57NAPCO
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Help, High idle problem TBI, how the heck do you get it down.

I have a 1988 Chevrolet V30, 7.4, 400 transmission. I have a high idle problem. On startup its idles way to high and never really drops down. Truck has low original miles on it. Changed...iac, tps, rebuilt TBI and new base gasket, pulled the egr and its not froze up, new fuel pump. Never touched the timing, could timing cause it on a TBI ? Sorry for the stupid question but Im not a technician, just a parts changer...
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Old 01-04-2018, 09:58 AM   #2
b454rat
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Re: Help, High idle problem TBI, how the heck do you get it down.

One of mine idled high, I turned the idle screw out some. But for whatever reason they have a plug that covers up the screw. I think there is a way to “reset” the IAC and TPS but not 100% if that adjusts idle speed or not.
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Old 01-04-2018, 05:30 PM   #3
Tiger Joe
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Re: Help, High idle problem TBI, how the heck do you get it down.

Coolant temp sensor will make it idle high too.

On the front of the intake. Our 92 454 rib would idle way high and that solved it
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Old 01-04-2018, 08:14 PM   #4
kwmech
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Re: Help, High idle problem TBI, how the heck do you get it down.

Did you replace the gasket under the adapter plate?
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Old 01-04-2018, 08:20 PM   #5
A1971Blazer
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Re: Help, High idle problem TBI, how the heck do you get it down.

check all the vacuum lines for cracking...high idle is usually a vacuum leak....
also as someone stated check the coolant temp sensor AND the connector....
but usually if either one is bad you will get a rich condition in addition to a high idle...if the pcm sees a cold engine condition it will dump in extra fuel....
also check the IAC for proper operation....this controls the amount of air going in at idle...
and check the TPS voltage at idle...you may need to tweak it a little.

read here...http://www.gmtuners.com/tech/TPS_IAC.htm
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Old 01-05-2018, 04:48 AM   #6
57NAPCO
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Re: Help, High idle problem TBI, how the heck do you get it down.

Quote:
Originally Posted by kwmech View Post
Did you replace the gasket under the adapter plate?
Yes I did, also rebuilt the TBI. Thanks
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Old 01-05-2018, 04:50 AM   #7
57NAPCO
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Re: Help, High idle problem TBI, how the heck do you get it down.

Quote:
Originally Posted by A1971Blazer View Post
check all the vacuum lines for cracking...high idle is usually a vacuum leak....
also as someone stated check the coolant temp sensor AND the connector....
but usually if either one is bad you will get a rich condition in addition to a high idle...if the pcm sees a cold engine condition it will dump in extra fuel....
also check the IAC for proper operation....this controls the amount of air going in at idle...
and check the TPS voltage at idle...you may need to tweak it a little.

read here...http://www.gmtuners.com/tech/TPS_IAC.htm
Good stuff, Ill order the coolant sensor, they are cheap.

Good reading on the link, thanks.
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Old 01-05-2018, 03:52 PM   #8
DieselSJ
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Re: Help, High idle problem TBI, how the heck do you get it down.

If you rebuilt it, follow the steps for the minimum idle setting.

Also, get a ALDL cable and download a scanning app and you won't need to guess about whether sensors are good.
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Old 01-06-2018, 10:31 AM   #9
57NAPCO
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Re: Help, High idle problem TBI, how the heck do you get it down.

Quote:
Originally Posted by DieselSJ View Post
If you rebuilt it, follow the steps for the minimum idle setting.

Also, get a ALDL cable and download a scanning app and you won't need to guess about whether sensors are good.
Thanks for the info, I certainly need the ALDL set up but I ditched all my PC stuff and drank the apple coolaide
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Old 01-06-2018, 07:52 PM   #10
57NAPCO
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Re: Help, High idle problem TBI, how the heck do you get it down.

Where the heck is the coolant temp sensor anyway ?
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Old 01-06-2018, 10:35 PM   #11
Tiger Joe
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Re: Help, High idle problem TBI, how the heck do you get it down.

I said on our 92 it’s right by the thermostat front of the intake not sure if 88 is the same know it’s a different manifold
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