l98 starts rough, idles rough today
Thread Starter
Le Mans Master
Joined: Mar 2001
Posts: 9,739
Likes: 0
From: A Pretty Part of MO
l98 starts rough, idles rough today
The vette has been running fine until today. I started it up this evening, and it is stumbling. Check engine light comes on. The exhaust smells real rich. Where should I start checking? I'm thinking spark. The car has 66k on it, and I think the plugs and wires are still the original ones. What else could I check?
thanks,
chris
thanks,
chris
Team Owner
Joined: Sep 2001
Posts: 62,119
Likes: 1,725
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Re: l98 starts rough, idles rough today (MtlSphere)
i'm leaning towards MAF right now
crap, no MAF on 90-91. hmmmmmmm
[Modified by vader86, 9:30 AM 8/10/2003]
crap, no MAF on 90-91. hmmmmmmm
[Modified by vader86, 9:30 AM 8/10/2003]
Burning Brakes
Joined: Oct 2002
Posts: 835
Likes: 3
From: Water Winter Wonderland
Re: l98 starts rough, idles rough today (90qzrblu)
Read the code(s). But here's my predictions:
The car doesn't use feedback from the O2 sensor until going closed loop (about three minutes after starting up a cold motor). SO even though it's probably time for a new O2 sensor, I don't think a bad one will make your car run crappy when cold.
If I'm reading your handle correctly, you have a 1990. No MAF on a 90. But a crummy MAP will make the car practically unable to run. Thing is, MAPS are very reliable.
I'm guessing plug or plug wire. After 66,000 miles, man, it could use a tune up!
Do we get a prize for guessing correctly?! Be sure to let us know what you find.
[Modified by ELEVENS, 7:55 AM 8/10/2003]
The car doesn't use feedback from the O2 sensor until going closed loop (about three minutes after starting up a cold motor). SO even though it's probably time for a new O2 sensor, I don't think a bad one will make your car run crappy when cold.
If I'm reading your handle correctly, you have a 1990. No MAF on a 90. But a crummy MAP will make the car practically unable to run. Thing is, MAPS are very reliable.
I'm guessing plug or plug wire. After 66,000 miles, man, it could use a tune up!
Do we get a prize for guessing correctly?! Be sure to let us know what you find.
[Modified by ELEVENS, 7:55 AM 8/10/2003]
Advanced
Joined: May 2003
Posts: 60
Likes: 0
Re: l98 starts rough, idles rough today (90qzrblu)
I had this happen a couple years ago on my '90. I pulled up to a stop light, it's idling great, then all of the sudden it's idling rough as h**l. I got it home, the exaust smells rich. I can't remember if it set a code or not. I pulled the plugs and found #7 wet with gas. The injector was stuck wide open.
Good luck,
Bill
Good luck,
Bill
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
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
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
Burning Brakes
Joined: Jul 2003
Posts: 811
Likes: 0
From: OH
St. Jude Donor '06-'07-'08-'09
Re: l98 starts rough, idles rough today (90qzrblu)
Try checking your fuel pressure. If the fuel pressure regulator goes bad, the fuel pressure will be too high at the injectors and blow right past them, causing the car to run rich. Happened to my 86 last year.
Good luck
Dan
Good luck
Dan
Thread Starter
Le Mans Master
Joined: Mar 2001
Posts: 9,739
Likes: 0
From: A Pretty Part of MO
Re: l98 starts rough, idles rough today (nitrous1)
Ok, i finally read the codes and got these:
15,21,43,53
The 21 and 43 are probably the ones I'm after. 21 is "throttle position sensor high" and 43 is "knock sensor circuit".
I would suppose that it spits these out in numerical order, and not the order in which the error occurred?
How do I check the throttle position sensor to adjust or replace? Also, where is the knock sensor and what does it do?
thanks alot guys,
chris
15,21,43,53
The 21 and 43 are probably the ones I'm after. 21 is "throttle position sensor high" and 43 is "knock sensor circuit".
I would suppose that it spits these out in numerical order, and not the order in which the error occurred?
How do I check the throttle position sensor to adjust or replace? Also, where is the knock sensor and what does it do?
thanks alot guys,
chris
Team Owner
Joined: Sep 2001
Posts: 62,119
Likes: 1,725
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Re: l98 starts rough, idles rough today (90qzrblu)
15- Coolant sensor circuit, has your coolant temperature been freaky or too high?
21-TPS, check its voltage and the connections first, then youll probably have to replace it
53-system voltage too high
43-Knock sensor, check for wiring shorts to ground and make sure wiring clears the exhaust, then replace the knock sensor
The knock sensor is VERY important, if it reads knock the ECM adjusts timing so you dont cook a piston.
All of these seem like voltage problems, so start at the TPS first, and that one might be triggering all these other codes. You always start at the front of the engine when it comes to SES codes. Clear the codes after fixing the TPS and see what comes back. I bet some of them disappear. The TPS sensor is on the side of the TB
21-TPS, check its voltage and the connections first, then youll probably have to replace it
53-system voltage too high
43-Knock sensor, check for wiring shorts to ground and make sure wiring clears the exhaust, then replace the knock sensor
The knock sensor is VERY important, if it reads knock the ECM adjusts timing so you dont cook a piston.
All of these seem like voltage problems, so start at the TPS first, and that one might be triggering all these other codes. You always start at the front of the engine when it comes to SES codes. Clear the codes after fixing the TPS and see what comes back. I bet some of them disappear. The TPS sensor is on the side of the TB
Thread Starter
Le Mans Master
Joined: Mar 2001
Posts: 9,739
Likes: 0
From: A Pretty Part of MO
Re: l98 starts rough, idles rough today (vader86)
Ok, I got the TPS sensor changed, and still nothing different. I did notice that the engine sounds like I've got a supercharger on it. Like a whistling that changes pitch with RPM. Maybe I've got a huge vaccuum leak? Would that cause codes like what I got?
Team Owner
Joined: Sep 2001
Posts: 62,119
Likes: 1,725
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Re: l98 starts rough, idles rough today (90qzrblu)
the code 21 came back after you cleared them?
a vacuum leak might cause the 21 if the wiring is good, then that triggers the rest
a vacuum leak might cause the 21 if the wiring is good, then that triggers the rest
Thread Starter
Le Mans Master
Joined: Mar 2001
Posts: 9,739
Likes: 0
From: A Pretty Part of MO
Re: l98 starts rough, idles rough today (vader86)
Well, I changed the TPS on thursday. Still ran rough. I went back out today (sunday), cleared the codes out, and it idles just fine now!!!
:party: :party: :party:
Thanks alot, Vader! I've got my vette back now.... :D
:party: :party: :party:
Thanks alot, Vader! I've got my vette back now.... :D
