Throttle Body Will Not Close Completely
Thread Starter
Racer
Joined: Jun 2007
Posts: 367
Likes: 0
From: Springfield MA
Throttle Body Will Not Close Completely
Hey guys I really need you experience/ideas on this one.
1989 L98 6 speed, Throttle Body Will Not Close Completely. It is staying open about 1/8". If I close it by hand the engine runs perfect.
So I replaced all 8 fuel injectors (22lbs) this weekend. Added a Adjustable Fuel Pressure Regulator (42.5psi) & new EGR valve. I also did a coolant bypass on the throttle body and Cleaned the TB with a can of carb cleaner.
This problem DID existed before I replaced the fuel injectors. (I did think it was a by-product of the bad fuel injector)
I did check the TPS and it was a perfect .58 @ idle (& 4.3 WOT). I did not attempt to adjust the IAC.
While I was driving I guessed it would be some vacuum hose but know i feel a bit lost. It did fell like it was down on power but I can say for certain.
All ideas welcome.
Fingers crossed I dont need a new TB
1989 L98 6 speed, Throttle Body Will Not Close Completely. It is staying open about 1/8". If I close it by hand the engine runs perfect.
So I replaced all 8 fuel injectors (22lbs) this weekend. Added a Adjustable Fuel Pressure Regulator (42.5psi) & new EGR valve. I also did a coolant bypass on the throttle body and Cleaned the TB with a can of carb cleaner.
This problem DID existed before I replaced the fuel injectors. (I did think it was a by-product of the bad fuel injector)
I did check the TPS and it was a perfect .58 @ idle (& 4.3 WOT). I did not attempt to adjust the IAC.
While I was driving I guessed it would be some vacuum hose but know i feel a bit lost. It did fell like it was down on power but I can say for certain.
All ideas welcome.
Fingers crossed I dont need a new TB
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
Did you try adjusting the idle-stop screw? If TPS is set "correctly", maybe someone opened it, and reset the TPS. Maybe they did so -- in response to bad injectors?
Seems like you'd be running too fast on the idle though....after swapping in new injectors.
No way it SHOULDn't be running (idling) too fast with the TB open too much.
Maybe the timing is off too?
Seems like you'd be running too fast on the idle though....after swapping in new injectors.
No way it SHOULDn't be running (idling) too fast with the TB open too much.
Maybe the timing is off too?
Thread Starter
Racer
Joined: Jun 2007
Posts: 367
Likes: 0
From: Springfield MA
Hey guys thanks for the replies. I will check the linkage cables to be sure the move smoothly.
I didn't touch the idle screw since the factory plug was still installed and did not appear to ever been knocked out. Also when I had the bad fuel injector in the engine would idle as low as 450 while hot. Idk of that is worth anything though.
When I cleaned the tb it would snap back to the screw. It was in the 90s in Boston today. How outrageous would it be to think the weather is a factor? I'm guessing that isn't the sole issue but worth asking. Updates coming. Thanks again
I didn't touch the idle screw since the factory plug was still installed and did not appear to ever been knocked out. Also when I had the bad fuel injector in the engine would idle as low as 450 while hot. Idk of that is worth anything though.
When I cleaned the tb it would snap back to the screw. It was in the 90s in Boston today. How outrageous would it be to think the weather is a factor? I'm guessing that isn't the sole issue but worth asking. Updates coming. Thanks again
Thread Starter
Racer
Joined: Jun 2007
Posts: 367
Likes: 0
From: Springfield MA
Alright still scratching my head b/c of this one. First I checked the cables. They are taunt but not tight. Seemed like it is as it should be. I pulled the TB cables off and started the car. The TB would still not close completely on it own staying open just a bit to cause a high idle like yesterday.
I shut the car off and stroked the TB and it did shut as it should. So I was thinking vacuum leak. I sprayed carb cleaner on both ends of the runners, the ERG, the nozzle end of each injector, and the plenum side of the TB & the rev's stayed flat (judging with my ear). I have never tested Vacuum that way (or any way); so Im guessing that if there was a leak the rev's would pick up a noticeable amount.
I'm just realizing I should start the car and get it to stick open a bit and then shut the car off to see if it returns or stays put. I will do after work.
I guess that only leaves the timing to be checked. Can this be done with the ALDL cable I've read about? Or should I buy a timing light?
Both?
I have 22lbs/hr injectors @42.5 should the fuel pressure be higher than that?
I shut the car off and stroked the TB and it did shut as it should. So I was thinking vacuum leak. I sprayed carb cleaner on both ends of the runners, the ERG, the nozzle end of each injector, and the plenum side of the TB & the rev's stayed flat (judging with my ear). I have never tested Vacuum that way (or any way); so Im guessing that if there was a leak the rev's would pick up a noticeable amount.
I'm just realizing I should start the car and get it to stick open a bit and then shut the car off to see if it returns or stays put. I will do after work.
I guess that only leaves the timing to be checked. Can this be done with the ALDL cable I've read about? Or should I buy a timing light?
Both?
I have 22lbs/hr injectors @42.5 should the fuel pressure be higher than that?
Last edited by rube1975; Jun 25, 2013 at 01:38 PM.
Team Owner
Joined: Sep 2003
Posts: 20,179
Likes: 673
From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
If the butterflys are not closing completely when the cable is disconnected,
there is a mechanical problem with the TB.
Remove, disassemble, clean, inspect, reassemble.
Quit chasing around and get your initial problem fixed first.
there is a mechanical problem with the TB.
Remove, disassemble, clean, inspect, reassemble.
Quit chasing around and get your initial problem fixed first.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Hi, try this first before you do anything else!
This passed week, I was experiencing the same problem. I would drive and come to a stop light and idle at 1100 - 1400 rpms at times. The only way to get it to stop would be to tap the gas. So I figured it wouldn't be the IAC valve since tapping the gas stopped the problem temporarily, so I thought, okay, stuck throttle plate.
I pulled over when it happened one day and I did notice my throttle plate was open a little bit, and when I closed it the problem went away. I brought it hope, took off the snorkel, and sprayed the linkage and all pivot points of the cables with WD40. I opened the throttle body and sprayed the throttle plate bores (4 internal). Then I also sprayed the bore on the outside right next to the TPS. Work the throttle plate back and forth while you keep do this 5 times. Get in your car and go for a ride. Mine got stuck one more time, and then the WD40 worked its way in and it doesn't do this anymore.
If this solution doesn't work, because it doesn't always, then you will need a new throttle body. If it comes down to that, I recommend go with a bigger throttle body, (if you want to put some more power into it.), but if you aren't going to put a bigger intake into the car, or port and polish, then don't go too big.
Best of luck to you!
This passed week, I was experiencing the same problem. I would drive and come to a stop light and idle at 1100 - 1400 rpms at times. The only way to get it to stop would be to tap the gas. So I figured it wouldn't be the IAC valve since tapping the gas stopped the problem temporarily, so I thought, okay, stuck throttle plate.
I pulled over when it happened one day and I did notice my throttle plate was open a little bit, and when I closed it the problem went away. I brought it hope, took off the snorkel, and sprayed the linkage and all pivot points of the cables with WD40. I opened the throttle body and sprayed the throttle plate bores (4 internal). Then I also sprayed the bore on the outside right next to the TPS. Work the throttle plate back and forth while you keep do this 5 times. Get in your car and go for a ride. Mine got stuck one more time, and then the WD40 worked its way in and it doesn't do this anymore.
If this solution doesn't work, because it doesn't always, then you will need a new throttle body. If it comes down to that, I recommend go with a bigger throttle body, (if you want to put some more power into it.), but if you aren't going to put a bigger intake into the car, or port and polish, then don't go too big.
Best of luck to you!
Thread Starter
Racer
Joined: Jun 2007
Posts: 367
Likes: 0
From: Springfield MA
Hey Dan Thanks for the tip it worked like a charm!
Hi, try this first before you do anything else!
This passed week, I was experiencing the same problem. I would drive and come to a stop light and idle at 1100 - 1400 rpms at times. The only way to get it to stop would be to tap the gas. So I figured it wouldn't be the IAC valve since tapping the gas stopped the problem temporarily, so I thought, okay, stuck throttle plate.
I pulled over when it happened one day and I did notice my throttle plate was open a little bit, and when I closed it the problem went away. I brought it hope, took off the snorkel, and sprayed the linkage and all pivot points of the cables with WD40. I opened the throttle body and sprayed the throttle plate bores (4 internal). Then I also sprayed the bore on the outside right next to the TPS. Work the throttle plate back and forth while you keep do this 5 times. Get in your car and go for a ride. Mine got stuck one more time, and then the WD40 worked its way in and it doesn't do this anymore.
If this solution doesn't work, because it doesn't always, then you will need a new throttle body. If it comes down to that, I recommend go with a bigger throttle body, (if you want to put some more power into it.), but if you aren't going to put a bigger intake into the car, or port and polish, then don't go too big.
Best of luck to you!
This passed week, I was experiencing the same problem. I would drive and come to a stop light and idle at 1100 - 1400 rpms at times. The only way to get it to stop would be to tap the gas. So I figured it wouldn't be the IAC valve since tapping the gas stopped the problem temporarily, so I thought, okay, stuck throttle plate.
I pulled over when it happened one day and I did notice my throttle plate was open a little bit, and when I closed it the problem went away. I brought it hope, took off the snorkel, and sprayed the linkage and all pivot points of the cables with WD40. I opened the throttle body and sprayed the throttle plate bores (4 internal). Then I also sprayed the bore on the outside right next to the TPS. Work the throttle plate back and forth while you keep do this 5 times. Get in your car and go for a ride. Mine got stuck one more time, and then the WD40 worked its way in and it doesn't do this anymore.
If this solution doesn't work, because it doesn't always, then you will need a new throttle body. If it comes down to that, I recommend go with a bigger throttle body, (if you want to put some more power into it.), but if you aren't going to put a bigger intake into the car, or port and polish, then don't go too big.
Best of luck to you!