87' TBI High Idle - The 1947 - Present Chevrolet & GMC Truck Message Board Network

.38 special · 11-01-2003, 01:05 AM

My first post, seems like a cool board.
I have a TBI 350 in my 87 GMC. Since I have owned it (3months) it has had a pretty high idle off and on. I tried to fix the problem by adjusting the tps which was at .74--I adjusted it to .41 like it said in the manual. This did not fix the problem, it is idling at like 1800 rpm. Please help

Low87 · 11-01-2003, 09:13 AM

Welcome to the board! I've had my share of nightmares with TBI. Check the IAC (idle air control valve). It could either be bad or just have come loose. 1st time I rebuilt my TBI I forgot to plug it back in, idled very high until I realized what I had done. Good luck, as Mike (swervin ervin) and I can attest to, diagnosing TBI problems is kind of like Vegas and the stock market.

**swervin ervin** · 11-01-2003, 10:52 AM

I had a high idle on my 87 van too. Replaced everything on it trying to fix it. I rebuilt the throttle body, still nothing. Finally I replaced the throttle body after noticing the original one had slop in the throttle shaft. Only thing I can figure is it was a vacuum leak around the shaft.

.38 special · 11-01-2003, 01:48 PM

I was thinking IAC too, but HOW DO I RESET IT or is there a way to reset it. I tried the way I reset my turbo Buick, but to no avail. Thanks for the speedy response already.

Low87 · 11-01-2003, 07:11 PM

I don't know of a way to reset it. I can pay forward a favor Mike did me and send you a used but working IAC. Just pm me your address and I'll have it in the mail Monday.

87 STEPPER · 11-01-2003, 07:33 PM

Welcome,

First thing i would look at is the IAC as mentioned if it has a black build up on it (known as cokeing) clean it and then remove the TBI and clean the pintal seat and the air cavity under neath it if it's got build up and then reinstall it.

To reset the IAC for the proper idle jumper the diagonstic pins on the ALDL A&B then turn the ignition on and the IAC motor will be driven to the full closed position, With the ign. still on and the ALDL pins jumpered go unplug the connector on the IAC valve then turn off the ign. and remove the ALDL jumper now reconnect the IAC plug and start the truck you have just reset what's called (minimum air gap).

IMO TBI system's are very easy to trouble shoot and understand if you have the correct diagonstic tool's and a factory maintenance manual the ECM computer will tell you every thing you need to know in order to fix it. That and with a little common sense your set.

**swervin ervin** · 11-01-2003, 08:55 PM

Yeah, that's easy for you to say. One thing about them, it's expensive to replace the stuff that quits working.

Now, a carb. I can turn one inside out. TBI sucks IMO. I flat out don't like having a computer telling my vehicles what to do. It's like everything is out of my control. I don't like not being in control.

Oh, and I have plenty of common sense. As a matter of fact, it's the only kind of sense I do have.

87 STEPPER · 11-01-2003, 10:44 PM

Quote:

Originally posted by swervin ervin

Oh, and I have plenty of common sense. As a matter of fact, it's the only kind of sense I do have.

Mike,

That statement was in no way ment as an insult to you or any one else and i hope you didn't take it that way.

.38 special · 11-01-2003, 10:47 PM

Man, you guys are great. Honestly I didn't expect this good of a response, I figured everyone on here had a carb. I will definately hit you up LOW87 if what what 87STEPPER wrote doesn't work.

One stupid question 87Stepper: which ones are A and B?
Top left two?

87 STEPPER · 11-01-2003, 10:54 PM

Quote:

Originally posted by .38 special

One stupid question 87Stepper: which ones are A and B?
Top left two?

No. the top right two

And it's not a stupid question.

**swervin ervin** · 11-01-2003, 11:48 PM

Bruce,

didn't take it that way. It's my dry sense of humor shining through. I knew what you were talking about. I thought I would add some humor.

.38 special · 11-02-2003, 12:28 AM

I'll post results tommorrow.
Thanks again.

Low87 · 11-04-2003, 01:34 PM

Quote:

Originally posted by .38 special
I'll post results tommorrow.
Thanks again.

Well?

1976K5CHALET · 11-08-2003, 03:26 AM

Okay...gotta join the post on this one...as i am well versed in tbi's and some of there quirks...but they do eat my lunch from time to time....and this time i have the same problem.

After the engine warms up...in gear..at a light...the wifes 90 V2500 Burb gets the hunting idle problem...and it is driving me batty...

Thouhgt...at thats what i get for thinking...that i had it solved....i have my own snap on scanner...and as a deisel tech...lol...i only use it at home...brought home my infra red temp gun and checked the CTS vs. actual temp early one am before work..outside temp was 37 degree's...block temp near cts around 40...ecm seeing 76 degree's....so pull out known good spare...amazing how a S60 detroit deisel uses the same sensor....hehehe. Let it warm up to operating temp...put it gear...let it idle away with P/B set for a half hour or so..not even a peep....wife gets in it the next day and we are back to square one again...

First tbi had the dreaded worn out tbi shaft syndrome....spare went on and we have the same problem...i give...uncle. Any thoughts out there. Its amazing that i have the skills to build my own tbi harness from a donor truck....have the experience of retro fiting 2 old k5's from carbs to tbi....lucky enough to have a laptop to run winaldl so i can save raw data to get a new chip burned....but i can't fix a stupid idle problem....lol.

Any other thoughts and help would be greatly appreciated...

DW

.38 special · 11-11-2003, 10:03 PM

Sorry it took so long to respond. But the site was down, and at the worse possible time for me.
I had my hands on an OTC 2000, but couldn't really figure it out without the help of the board.
The problem was (of course) simpler than I thought. I had a leak in the tb to intake gasket.
But after fiddling with everything I could get my hands on to fix it--now that I fixxed it I have a very low idle--400rpm.
I couldn't access this post to find out how to re-reset the IAC.

Now it will have to wait though because I took it to the tranny shop, I just installed a rebuilt and it is taking like 7 seconds to downshift. So he'll have to fix it.

By the way, it has always had a pretty high idle. At the beginning of the post, I reset the TPS, and a bolt broke in the TB. I had to remove it to drill and retapp. Thats why I didn't have a good seal in the gasket, I guess I was scared to really torque on it after breaking the tps bolt.

Thanks everyone for all the help.
I will ask more questions if I can't figure out the low idle problem.
and I'll be a regular.

Low87 · 11-12-2003, 10:46 AM

Quote:

Originally posted by .38 special
and I'll be a regular.

Sorry, we can't allow you to be a regular until you post a picture of your truck.

**Captkaos** · 11-12-2003, 06:20 PM

Quote:

Originally posted by swervin ervin
TBI sucks IMO. I flat out don't like having a computer telling my vehicles what to do. It's like everything is out of my control.

Rather depend on vacuum telling your vehicle what to do huh?

Brings a whole new meaning to blowing/sucking hot air...

BTW, primitive computers use vacuum to calculate also..... so... sounds like you have something primitive "computing" your settings.

**swervin ervin** · 11-12-2003, 06:31 PM

OK, we're even.

.38 special · 11-12-2003, 06:39 PM

My truck is pretty plain, very clean though. When I get it back, I'll clean it really good and get it posted, I hope you don't mind that a turbo buick will be in the background.

11-01-2003, 01:05 AM	#1
.38 special Registered User Join Date: Oct 2003 Location: Houston area Posts: 65	87' TBI High Idle My first post, seems like a cool board. I have a TBI 350 in my 87 GMC. Since I have owned it (3months) it has had a pretty high idle off and on. I tried to fix the problem by adjusting the tps which was at .74--I adjusted it to .41 like it said in the manual. This did not fix the problem, it is idling at like 1800 rpm. Please help

11-01-2003, 09:13 AM	#2
Low87 been here longer than Liz Join Date: Feb 2000 Location: Broken Arrow, OK Posts: 2,437	Welcome to the board! I've had my share of nightmares with TBI. Check the IAC (idle air control valve). It could either be bad or just have come loose. 1st time I rebuilt my TBI I forgot to plug it back in, idled very high until I realized what I had done. Good luck, as Mike (swervin ervin) and I can attest to, diagnosing TBI problems is kind of like Vegas and the stock market. __________________ ~Greg~ Mac's Garage '87 SWB 6/8 drop "Piso" '08 CCSB Silverado DD the departed '89 GMC K5 Jimmy 4x4 "Rusty Nuts" '77 Chevy K5 Blazer 2wd '83 Chevy stepside "You get what you pay for" - Mike 'swervin ervin' Ervin

11-01-2003, 10:52 AM	#3
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	I had a high idle on my 87 van too. Replaced everything on it trying to fix it. I rebuilt the throttle body, still nothing. Finally I replaced the throttle body after noticing the original one had slop in the throttle shaft. Only thing I can figure is it was a vacuum leak around the shaft. __________________ Mike 1985 Chevy C-10

11-01-2003, 07:11 PM	#5
Low87 been here longer than Liz Join Date: Feb 2000 Location: Broken Arrow, OK Posts: 2,437	I don't know of a way to reset it. I can pay forward a favor Mike did me and send you a used but working IAC. Just pm me your address and I'll have it in the mail Monday. __________________ ~Greg~ Mac's Garage '87 SWB 6/8 drop "Piso" '08 CCSB Silverado DD the departed '89 GMC K5 Jimmy 4x4 "Rusty Nuts" '77 Chevy K5 Blazer 2wd '83 Chevy stepside "You get what you pay for" - Mike 'swervin ervin' Ervin

11-01-2003, 07:33 PM	#6
87 STEPPER STILL PLAYS WITH TRUX Join Date: Nov 2002 Location: Melbourne, Fla. Posts: 2,764	Welcome, First thing i would look at is the IAC as mentioned if it has a black build up on it (known as cokeing) clean it and then remove the TBI and clean the pintal seat and the air cavity under neath it if it's got build up and then reinstall it. To reset the IAC for the proper idle jumper the diagonstic pins on the ALDL A&B then turn the ignition on and the IAC motor will be driven to the full closed position, With the ign. still on and the ALDL pins jumpered go unplug the connector on the IAC valve then turn off the ign. and remove the ALDL jumper now reconnect the IAC plug and start the truck you have just reset what's called (minimum air gap). IMO TBI system's are very easy to trouble shoot and understand if you have the correct diagonstic tool's and a factory maintenance manual the ECM computer will tell you every thing you need to know in order to fix it. That and with a little common sense your set. __________________ ~~Bruce~~ MY 87 STEPPER MY 99 2D/WD TAHOE

11-01-2003, 01:48 PM	#4
.38 special Registered User Join Date: Oct 2003 Location: Houston area Posts: 65	I was thinking IAC too, but HOW DO I RESET IT or is there a way to reset it. I tried the way I reset my turbo Buick, but to no avail. Thanks for the speedy response already.

11-01-2003, 08:55 PM	#7
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Yeah, that's easy for you to say. One thing about them, it's expensive to replace the stuff that quits working. Now, a carb. I can turn one inside out. TBI sucks IMO. I flat out don't like having a computer telling my vehicles what to do. It's like everything is out of my control. I don't like not being in control. Oh, and I have plenty of common sense. As a matter of fact, it's the only kind of sense I do have. __________________ Mike 1985 Chevy C-10

11-01-2003, 10:47 PM	#9
.38 special Registered User Join Date: Oct 2003 Location: Houston area Posts: 65	Man, you guys are great. Honestly I didn't expect this good of a response, I figured everyone on here had a carb. I will definately hit you up LOW87 if what what 87STEPPER wrote doesn't work. One stupid question 87Stepper: which ones are A and B? Top left two?

11-01-2003, 11:48 PM	#11
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Bruce, didn't take it that way. It's my dry sense of humor shining through. I knew what you were talking about. I thought I would add some humor. __________________ Mike 1985 Chevy C-10

11-02-2003, 12:28 AM	#12
.38 special Registered User Join Date: Oct 2003 Location: Houston area Posts: 65	I'll post results tommorrow. Thanks again.

11-08-2003, 03:26 AM	#14
1976K5CHALET Senior Member Join Date: Jan 2003 Location: Grand Junction, Colorado Posts: 611	Okay...gotta join the post on this one...as i am well versed in tbi's and some of there quirks...but they do eat my lunch from time to time....and this time i have the same problem. After the engine warms up...in gear..at a light...the wifes 90 V2500 Burb gets the hunting idle problem...and it is driving me batty... Thouhgt...at thats what i get for thinking...that i had it solved....i have my own snap on scanner...and as a deisel tech...lol...i only use it at home...brought home my infra red temp gun and checked the CTS vs. actual temp early one am before work..outside temp was 37 degree's...block temp near cts around 40...ecm seeing 76 degree's....so pull out known good spare...amazing how a S60 detroit deisel uses the same sensor....hehehe. Let it warm up to operating temp...put it gear...let it idle away with P/B set for a half hour or so..not even a peep....wife gets in it the next day and we are back to square one again... First tbi had the dreaded worn out tbi shaft syndrome....spare went on and we have the same problem...i give...uncle. Any thoughts out there. Its amazing that i have the skills to build my own tbi harness from a donor truck....have the experience of retro fiting 2 old k5's from carbs to tbi....lucky enough to have a laptop to run winaldl so i can save raw data to get a new chip burned....but i can't fix a stupid idle problem....lol. Any other thoughts and help would be greatly appreciated... DW __________________ Doug Wright aka K5NUTT over @coloradok5.com Owner of http://groups.yahoo.com/group/ChevyK5BlazerChalets Certified K5 Nut

11-11-2003, 10:03 PM	#15
.38 special Registered User Join Date: Oct 2003 Location: Houston area Posts: 65	Sorry it took so long to respond. But the site was down, and at the worse possible time for me. I had my hands on an OTC 2000, but couldn't really figure it out without the help of the board. The problem was (of course) simpler than I thought. I had a leak in the tb to intake gasket. But after fiddling with everything I could get my hands on to fix it--now that I fixxed it I have a very low idle--400rpm. I couldn't access this post to find out how to re-reset the IAC. Now it will have to wait though because I took it to the tranny shop, I just installed a rebuilt and it is taking like 7 seconds to downshift. So he'll have to fix it. By the way, it has always had a pretty high idle. At the beginning of the post, I reset the TPS, and a bolt broke in the TB. I had to remove it to drill and retapp. Thats why I didn't have a good seal in the gasket, I guess I was scared to really torque on it after breaking the tps bolt. Thanks everyone for all the help. I will ask more questions if I can't figure out the low idle problem. and I'll be a regular.

11-12-2003, 06:31 PM	#18
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	OK, we're even.

11-12-2003, 06:39 PM	#19
.38 special Registered User Join Date: Oct 2003 Location: Houston area Posts: 65	My truck is pretty plain, very clean though. When I get it back, I'll clean it really good and get it posted, I hope you don't mind that a turbo buick will be in the background.



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