Idle problem on a 94 tbi - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Ackattack · 01-01-2014, 08:03 PM

So driving around, my truck has developed an idle problem when I come to a stop. It will stumble real bad (sometimes) and has died a few times. Other than that it drives fine.

So I started checking stuff and took out the IAC to clean it. When I put it back in, I over tightened it, so I removed the TBI assembly and got the IAC out. Cleaned up the TBI assembly and reinstalled with a new gasket and new IAC. No change in the idle.

Then today I started messing with it again. I had it in park and stepped on the brake and the idle sped up and then dropped back down. So my suspicion is a problem with with the brake booster or check valve.

Before I go replace the brake booster, I wanted some input from others.

**Palf70Step** · 01-02-2014, 12:15 PM

I agree with you, but honestly don't know any other checks other than plugging the manifold where the booster is connected to see if it goes away there.

sntrym95 · 01-02-2014, 02:26 PM

Could also be the MAP sensor or EGR valve but most likely a vacuum leak - either in the brake booster or on the manifold/TBI.

Tx Firefighter · 01-02-2014, 02:55 PM

Stumbling idle and dying at idle also points to EGR valve sticking slightly open.

mgchevyparts · 01-02-2014, 11:26 PM

Bad booster will be a vacuum leak when you depress pedal, eliminate booster and see if it runs fine.

01-01-2014, 08:03 PM	#1
Ackattack Senior Member Join Date: Aug 2002 Location: Valley Center KS Posts: 3,525	Idle problem on a 94 tbi So driving around, my truck has developed an idle problem when I come to a stop. It will stumble real bad (sometimes) and has died a few times. Other than that it drives fine. So I started checking stuff and took out the IAC to clean it. When I put it back in, I over tightened it, so I removed the TBI assembly and got the IAC out. Cleaned up the TBI assembly and reinstalled with a new gasket and new IAC. No change in the idle. Then today I started messing with it again. I had it in park and stepped on the brake and the idle sped up and then dropped back down. So my suspicion is a problem with with the brake booster or check valve. Before I go replace the brake booster, I wanted some input from others. __________________ Project Bruiser: 68 Pro-Touring C-10 5.3L / 4L60E Project Ironhide: 97 GMC Crew Cab 4x4 Cummins SOLD: '69 GMC 1/2T SWB TBI'd: Project No Buck Assembly Manual Index Sign up Thread!!! Factory Service Manual Index

01-02-2014, 12:15 PM	#2
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 48,486	Re: Idle problem on a 94 tbi I agree with you, but honestly don't know any other checks other than plugging the manifold where the booster is connected to see if it goes away there. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

01-02-2014, 02:26 PM	#3
sntrym95 Registered User Join Date: Jan 2006 Location: Big Pine Key, FL Posts: 758	Re: Idle problem on a 94 tbi Could also be the MAP sensor or EGR valve but most likely a vacuum leak - either in the brake booster or on the manifold/TBI. __________________ Mike

01-02-2014, 02:55 PM	#4
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Idle problem on a 94 tbi Stumbling idle and dying at idle also points to EGR valve sticking slightly open. __________________ I'm on the Instagram- @Gearhead_Kevin

01-02-2014, 11:26 PM	#5
mgchevyparts Registered User Join Date: Feb 2013 Location: Upland, Calif Posts: 698	Re: Idle problem on a 94 tbi Bad booster will be a vacuum leak when you depress pedal, eliminate booster and see if it runs fine. __________________ 1957 CHEVY 1/2 TON SHORT BED 1940 FORD 1/2 TON SHORT BED



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