When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have a 95 corvette, and I’m noticing that when I’m at idle in drive or park my rpm’s are around 950-1100. If I quickly press down on the gas and let go it drops back down to around 600. I cleaned up my throttle body this winter. Not 100% what could be causing this.
In all likelihood it is worn throttle shaft bushings. I believe this is a common failure. My 94 does the same thing intermittently, same RPM hangup around 1100 unless I tap the accelerator. Believe you need to replace the throttle body, I recall seeing a thread in the past about rebushing it also but not sure.
I'd be curious if there is a quick fix, or if there is a suggested lubricant to mitigate the effects.
Last edited by Soundwave; May 17, 2025 at 02:21 PM.
Reason: typo
This is likely a common issue with any throttle body if the butterflies come in contact with the throttle bore. Here's the likely sequence of events leading up to this:
1. There's a vacuum leak in the system, can be cracked lines, degraded manifold seals, any leak in the vehicle's vacuum system, cruise control diaphragm, heater vent controls, or even the throttle body as mentioned.
2. The throttle stop is backed off in order to tune out the leak in the system, to tame the high idle, stumbling at initial throttle, and slow to drop idle (that's caused by a lean of stoich idle mixture)
3. The butterfly contacting the bore creates a slight burr as the steel blade sits on soft aluminum alloy, vibrating and impacting frequently. Then if you gently release the throttle to idle, it gets caught up on the burr which may also have sticky carbon residue to help the process.
So, make sure that the throttle linkage idle stop (sometimes there's a cap on the screw) contacts well before the butterfly blades contact the bore... and any adjustment also means reset the TPS.
Another sign of this is the IAC goes to zero duty cycle at idle when the engine is warm, it shouldn't be at zero, but ideally close to it. All points to a vacuum leak, can be troubleshot with a smoke generator.
I had this exact same issue on my '96. Before you try replacing the throttle body or bushings try this:
- Buy throttle body gasket set: Standard Motor P/N 2009. It's $15 on amazon prime or elsewhere. This includes the gasket for the top plate as well as the IAC housing plus extras for different years. You only need those two plus the gasket at the manifold. I found when I took it apart the gasket for the top plate had basically been sucked into the ports-no wonder had goofy idle problems.
- Disassemble and clean the entire throttle body w a toothbrush and cleaner. Make sure you open the butterflies and clean the edges too. Only use Throttle Body Cleaner. I had the same sticking problem and this took care of it. Just a bunch of carbon buildup.
- Make sure you take off the IAC and clean the tip too. I replaced mine since it was original w/ 135,000 miles on it.
- You don't have to take off the TPS to do this cleaning. It doesn't get dirty.
- Replace any and all vacuum lines you can find that even remotely look old. They're all on top of the engine and easy to get. Some of them are sized differently on each end-just get a heat gun/hair dryer and heat up the "big end" and it'll slide on.
This is likely a common issue with any throttle body if the butterflies come in contact with the throttle bore. Here's the likely sequence of events leading up to this:
1. There's a vacuum leak in the system, can be cracked lines, degraded manifold seals, any leak in the vehicle's vacuum system, cruise control diaphragm, heater vent controls, or even the throttle body as mentioned.
2. The throttle stop is backed off in order to tune out the leak in the system, to tame the high idle, stumbling at initial throttle, and slow to drop idle (that's caused by a lean of stoich idle mixture)
3. The butterfly contacting the bore creates a slight burr as the steel blade sits on soft aluminum alloy, vibrating and impacting frequently. Then if you gently release the throttle to idle, it gets caught up on the burr which may also have sticky carbon residue to help the process.
So, make sure that the throttle linkage idle stop (sometimes there's a cap on the screw) contacts well before the butterfly blades contact the bore... and any adjustment also means reset the TPS.
Another sign of this is the IAC goes to zero duty cycle at idle when the engine is warm, it shouldn't be at zero, but ideally close to it. All points to a vacuum leak, can be troubleshot with a smoke generator.
I just had all of that off to clean everything. It was filthy. I replaced bad hoses and put on new gaskets. I probably messed something up. I look through everything and see if something isn’t tight.
I just had all of that off to clean everything. It was filthy. I replaced bad hoses and put on new gaskets. I probably messed something up. I look through everything and see if something isn’t tight.
Did you ever figure this out? I'm going through something similar on my 85 and it's driving me insane
I have this issue on my 89. Have Completely replaced throttle body and problem persists. Only happens when vehicle is running. The higher the temp gauge the worse it gets. Put return springs on it to help but will still get stuck. Will even show the shift up light on dash. Usually sticks around 11-1400rpm. If it sits to long and I snap throttle the car will stall but fires right back up. My cruise control cable is not hooked to the tb. Again this only happens at temp while running. If I leave throttle stuck and shut car off you can hear it snap close. All vac lines were replaced when the engine was torn down. Except the cruise control unit cause I planned on removing it but unsure if it will throw a check engine light or not.
I have this issue on my 89. Have Completely replaced throttle body and problem persists. Only happens when vehicle is running. The higher the temp gauge the worse it gets. Put return springs on it to help but will still get stuck. Will even show the shift up light on dash. Usually sticks around 11-1400rpm. If it sits to long and I snap throttle the car will stall but fires right back up. My cruise control cable is not hooked to the tb. Again this only happens at temp while running. If I leave throttle stuck and shut car off you can hear it snap close. All vac lines were replaced when the engine was torn down. Except the cruise control unit cause I planned on removing it but unsure if it will throw a check engine light or not.
I've sent my throttle body off to SPR Performance to be cleaned and rebuilt with needle bearings. I'll update on if it helped or not when I get it back on the car. I've heard others say having their throttle shaft rebushed cleared up this issue.
it will work ghost. as long as you follow the min idle setting procedure.
it is a surprisingly small amount of wear that will cause the binding. a return spring will work but looks horrible and messes up with the pedal resistance.
it will work ghost. as long as you follow the min idle setting procedure.
it is a surprisingly small amount of wear that will cause the binding. a return spring will work but looks horrible and messes up with the pedal resistance.
Yeah my factory throttle body had a lot of play in it, then the one I bought off eBay had new bushings installed at some point but still had a little slop, so it would bind up when the engine got hot.
it will work ghost. as long as you follow the min idle setting procedure.
it is a surprisingly small amount of wear that will cause the binding. a return spring will work but looks horrible and messes up with the pedal resistance.
Curious though, what about it doing that on a new throttle body.
this will 100% need to be done when the refurbished tb comes back.
All it takes is a volt meter. Peel back the loom on the tps a very very small knick in the wires (u will have to look up which two, cant recall off too of mind) and set it up. I use 550rpm for iac closed on 84’s + 85’s and 500rpm on 86+.
this will 100% need to be done when the refurbished tb comes back.
All it takes is a volt meter. Peel back the loom on the tps a very very small knick in the wires (u will have to look up which two, cant recall off too of mind) and set it up. I use 550rpm for iac closed on 84’s + 85’s and 500rpm on 86+.
It's the top two wires, set to .54V, though I've heard of people setting it slightly lower so the IAC comes on quicker as you return to idle.
this will 100% need to be done when the refurbished tb comes back.
All it takes is a volt meter. Peel back the loom on the tps a very very small knick in the wires (u will have to look up which two, cant recall off too of mind) and set it up. I use 550rpm for iac closed on 84’s + 85’s and 500rpm on 86+.
Already did the relearn procedures. And what I was referring to was the binding. My tb is new. And it doesn't "bind" when the car is off. Only while running.
Sticky Throttle
