Odd Idle
Thread Starter
Instructor
Joined: Feb 2000
Posts: 154
Likes: 1
From: Gravette Arkansas
Odd Idle
Heres the deal...
Vette starts fine, no problems at all. Once running, however, the idle starts jumping all over the place between 500 and 1000 rpm. Secondly, the car is running extremely rich. When the engine is revved, once you let off the gas the engine backfires. You can smell it in the car too.
But thats not all...
Gas mileage is way down too.
I'm gussing it has to be fuel delivery. Perhaps clogged fuel filter? Possibly a bad O2 sensor?
Just wanted to get you guys' input before diagnosing to see if anyone has had a similar problem. Any suggestions?
Vette starts fine, no problems at all. Once running, however, the idle starts jumping all over the place between 500 and 1000 rpm. Secondly, the car is running extremely rich. When the engine is revved, once you let off the gas the engine backfires. You can smell it in the car too.
But thats not all...
Gas mileage is way down too.
I'm gussing it has to be fuel delivery. Perhaps clogged fuel filter? Possibly a bad O2 sensor?
Just wanted to get you guys' input before diagnosing to see if anyone has had a similar problem. Any suggestions?
Safety Car
Joined: Feb 2002
Posts: 4,212
Likes: 10
From: Sun City West Az
The O2(s) don't come into play until the ECM goes closed loop. If the symptoms are ocurring in open loop it could be several things. Any codes? The CTS, injecotrs, canister purging @ idle etc. Your going to have to trouble shoot it. I'd start with fp guage and a scanner to see whats going on.
Team Owner
Joined: Oct 2000
Posts: 96,443
Likes: 9
From: Fort Knox, KY
Cruise-In IV Veteran
Cruise-In VI Veteran
Cruise-In VII Veteran
Cruise-In VIII Veteran
What year? Your IAC pintle could be clogged, too. But I agree with ittlfly. Best to troubleshoot first with a fuel pressure guage and work your way out.
Pro
Joined: Mar 1999
Posts: 678
Likes: 0
From: Oslo, Norway
Hi.
It sounds like vacuum leak. Check the vacuum hoses and tubes. Then check the areas around the runners where they enter the manifold and plenum. That is easy to do. Take start gas or propane and "spray" it overthe area and see if the rpm increases immediately afterwards. I had that and the same symptom as you.
It sounds like vacuum leak. Check the vacuum hoses and tubes. Then check the areas around the runners where they enter the manifold and plenum. That is easy to do. Take start gas or propane and "spray" it overthe area and see if the rpm increases immediately afterwards. I had that and the same symptom as you.
Thread Starter
Instructor
Joined: Feb 2000
Posts: 154
Likes: 1
From: Gravette Arkansas
Sorry guys...
To answer as many of the questions I can....
Not sure why my sig didn't post. It's an 89.
I changed the fuel filter about 4 years ago but the car was in storage for about 2 of those.
Oh yeah, one last thing I forgot to include...
When driving down the road, under moderate throttle, it "hiccups" and by that it's like it almost cuts out. Going to take a look at the vac lines this weekend. Lets hope it's nothing major!
To answer as many of the questions I can....
Not sure why my sig didn't post. It's an 89.
I changed the fuel filter about 4 years ago but the car was in storage for about 2 of those.
Oh yeah, one last thing I forgot to include...
When driving down the road, under moderate throttle, it "hiccups" and by that it's like it almost cuts out. Going to take a look at the vac lines this weekend. Lets hope it's nothing major!
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
Advanced
Joined: Mar 2001
Posts: 89
Likes: 1
From: ca
I don't like "It sounds like my..." trouble shooting, BUT. My M.A.F. sensor went out and it had every symptom including the backfire that you mentioned. Easy check. Pull the plug off and restart the engine. The computer will use a default setting from its memory and it will run better if that is the problem.
Thread Starter
Instructor
Joined: Feb 2000
Posts: 154
Likes: 1
From: Gravette Arkansas
Originally Posted by RichardJ
I don't like "It sounds like my..." trouble shooting, BUT. My M.A.F. sensor went out and it had every symptom including the backfire that you mentioned. Easy check. Pull the plug off and restart the engine. The computer will use a default setting from its memory and it will run better if that is the problem.
**New development: The voltage is down around 11.4 when running. Happened all of a sudden Friday night. I have changed out two alternators in the past 6 months and 1 battery. Sound like a parasitic drain to anyone else. Could this be causing my trouble somehow?