Engine roars at start up.
Thread Starter
Burning Brakes
Joined: Jan 2007
Posts: 921
Likes: 0
From: Houston TX
Engine roars at start up.
Hi all,
On an 85 L98 4+3, when I start the car the engine turns over once and instantly roars to a very high rpm then backs down. With the flow master exhaust, anyone within 20 feet will soil their shorts.
No other car I know of does this. Is it normal?
Thanks,
the beep
On an 85 L98 4+3, when I start the car the engine turns over once and instantly roars to a very high rpm then backs down. With the flow master exhaust, anyone within 20 feet will soil their shorts.
No other car I know of does this. Is it normal?
Thanks,
the beep
Thread Starter
Burning Brakes
Joined: Jan 2007
Posts: 921
Likes: 0
From: Houston TX
I can do relatively simple things but as soon as it gets involved, I'm in trouble.
Le Mans Master
Joined: Apr 2005
Posts: 6,413
Likes: 9
From: The Old Dominion
The two C4's I've owned both start up at a higher rpm than they idle at. I think that's quite normal. How high are you talking about? I'm talking like 2,000 rpm max, but it sure sounds loud with a loud exhaust. Personally I like it.
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: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
idle
mine does the same, except it's 800 RPM, then drops to 600 RPM.
I would expect that you have a vacuum leak, making the IAC ineffective, and the fuel management is relegated to the oxygen sensor, instead of the iac, throttle plates, and the O2 sensor. I am guesing the computer sees the position of the throttle position sensor, and reschedules the fuel.
for a minute there, I was afraid it was a white corvette forum.............
I would expect that you have a vacuum leak, making the IAC ineffective, and the fuel management is relegated to the oxygen sensor, instead of the iac, throttle plates, and the O2 sensor. I am guesing the computer sees the position of the throttle position sensor, and reschedules the fuel.
for a minute there, I was afraid it was a white corvette forum.............
Le Mans Master
Joined: Jan 2003
Posts: 5,858
Likes: 7
From: Santa Maria CA
Mine growls on cold startup. I think the eliminators are the problem.
When I ran open headers, I was nervous to start it.
Seriously though, at what RPM does it rise to and how long does it stay there? What does it do on warm startups? It's normal for it to idle a little high on cold startups then gradually drop to spec idle after a few minutes of warm up. The TPI won't idle at spec speed right out of a cold start. Mine idles at about 1,200 RPM then drops to my 650 RPM setting.
When I ran open headers, I was nervous to start it.
Seriously though, at what RPM does it rise to and how long does it stay there? What does it do on warm startups? It's normal for it to idle a little high on cold startups then gradually drop to spec idle after a few minutes of warm up. The TPI won't idle at spec speed right out of a cold start. Mine idles at about 1,200 RPM then drops to my 650 RPM setting.
Thread Starter
Burning Brakes
Joined: Jan 2007
Posts: 921
Likes: 0
From: Houston TX
Gotta love white Vette's.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
I'd clear memory from the ECM first - at least in the old days, it was rumored that you could train it to give it this humbling little blast by simply goosing the throttle for a couple hundred startups. Eventually, it was suppose to burn that activity into memory and you wouldn't have to do anything. Pretty cool? Beats me, but all the youngsters were trying it. Otherwise, your ECM parks that IAC pintle at something like a 160 counts everytime you shut it down. That makes for a quick restart, but the rpms are going to be up there. Scan to see where yours is.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Is this something a half-blind knucklehead would screw up and would actually be cheaper to have a real mechanic do?
