1981 Idle Surge/ Rough Idle Issues.
Thread Starter
6th Gear
Joined: Nov 2024
Posts: 6
Likes: 1
1981 Idle Surge/ Rough Idle Issues.
As mentioned in the title I’m having some idle issues on my 81 4 speed. It’s a completely bone stock car. I got it out for the winter and I started noticing some surging issues, I have the idle set to about 800 but it will begin to idle up to about 1400 (sometimes higher.) it also will occasionally just start to rough idle, ranging from 500 to 1200 rpm in about a second before stalling. I doubt it’s a carb issue because as soon as I give it gas I get perfect throttle response and it runs fine when I hold the throttle open.
I’m suspecting a vacuum leak of some sort or bad fuel, I had put non ethanol fuel in it for the winter and I’ve completely ran that fuel out and I’ve put 93 in hoping that would solve the issue but it’s only gotten worse. If anyone has had any similar issues I’d love to hear what was wrong with yours and any advice you have for fixing it.
Thanks,
Max
I’m suspecting a vacuum leak of some sort or bad fuel, I had put non ethanol fuel in it for the winter and I’ve completely ran that fuel out and I’ve put 93 in hoping that would solve the issue but it’s only gotten worse. If anyone has had any similar issues I’d love to hear what was wrong with yours and any advice you have for fixing it.
Thanks,
Max
Thread Starter
6th Gear
Joined: Nov 2024
Posts: 6
Likes: 1
Racer
Joined: Mar 2018
Posts: 395
Likes: 52
From: wilmington Ma
Use a smoke machine if you can get your hands on one , much better than spraying toxic chemicals all over your car , with vettes the vacuum leak could be up front with the head light stuff or inside under dash.
Advanced
Joined: Oct 2023
Posts: 72
Likes: 22
From: Greeley, CO
Advanced
Joined: Sep 2008
Posts: 59
Likes: 12
From: London Ontario, Canada
Idle surge
As mentioned in the title I’m having some idle issues on my 81 4 speed. It’s a completely bone stock car. I got it out for the winter and I started noticing some surging issues, I have the idle set to about 800 but it will begin to idle up to about 1400 (sometimes higher.) it also will occasionally just start to rough idle, ranging from 500 to 1200 rpm in about a second before stalling. I doubt it’s a carb issue because as soon as I give it gas I get perfect throttle response and it runs fine when I hold the throttle open.
I’m suspecting a vacuum leak of some sort or bad fuel, I had put non ethanol fuel in it for the winter and I’ve completely ran that fuel out and I’ve put 93 in hoping that would solve the issue but it’s only gotten worse. If anyone has had any similar issues I’d love to hear what was wrong with yours and any advice you have for fixing it.
Thanks,
Max
I’m suspecting a vacuum leak of some sort or bad fuel, I had put non ethanol fuel in it for the winter and I’ve completely ran that fuel out and I’ve put 93 in hoping that would solve the issue but it’s only gotten worse. If anyone has had any similar issues I’d love to hear what was wrong with yours and any advice you have for fixing it.
Thanks,
Max
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
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Max,
Due to your symptoms of good throttle response, I would question ignition system.
If you have the std HEI distributor, you could remove 3 - 4 plug wires from the cap, passenger side and lay the cap over on its side.
The harness clip will stay with the cap.
Use a dry shop towel and wipe the entire inside of the cap clean of carbon tracking.
Grab the rotor, rotate and see if it snaps back.
Then remove rotor and inspect the springs / weights underneath. Rusty? Dry? Needs some lube?
I suspect with your erratic RPMs, the IGN timing is all over the place. Up-down, up down.
Could be either mechanical advance or a defective vacuum advance canister.
If you have a Mity-Vac tool, see if the Vac Can will hold vacuum.
Due to your symptoms of good throttle response, I would question ignition system.
If you have the std HEI distributor, you could remove 3 - 4 plug wires from the cap, passenger side and lay the cap over on its side.
The harness clip will stay with the cap.
Use a dry shop towel and wipe the entire inside of the cap clean of carbon tracking.
Grab the rotor, rotate and see if it snaps back.
Then remove rotor and inspect the springs / weights underneath. Rusty? Dry? Needs some lube?
I suspect with your erratic RPMs, the IGN timing is all over the place. Up-down, up down.
Could be either mechanical advance or a defective vacuum advance canister.
If you have a Mity-Vac tool, see if the Vac Can will hold vacuum.
Safety Car
Joined: Jul 2005
Posts: 3,697
Likes: 833
From: WI
Guys say to save around the top of the engine with a piece of hose on an unlit propane torch. The propane will smooth out an engine when it is drawn in. Use care obviously. Make sure it's coming off high-idle.
Pro
Joined: Mar 2022
Posts: 564
Likes: 185
I have a smoke machine and it’s great at finding leaks in lines but useless for confirming leaks at the carb. Worn carb bushings sucking air and base gasket leaks can’t be confirmed with a smoke machine. Spraying carb cleaner around these points while it’s idling can.
Racer
Joined: Mar 2018
Posts: 395
Likes: 52
From: wilmington Ma
