Running Rough at Idle
Thread Starter
Le Mans Master
Joined: Aug 2010
Posts: 5,339
Likes: 546
From: Central Texas
Running Rough at Idle
Hello,
I posted this problem before. I changed the plug wires and plugs and the car seemed to run better but not like it should. It's a 2008 auto with a tune. It's got 92,000 miles roughly.
What's the common culprits in this situation? Are the injectors prone to problems? Valves need some adjustments? Tps sensor?
I hang out in the C3 Forum so sorry if this is a common problem with a common solution.
Craig
I posted this problem before. I changed the plug wires and plugs and the car seemed to run better but not like it should. It's a 2008 auto with a tune. It's got 92,000 miles roughly.
What's the common culprits in this situation? Are the injectors prone to problems? Valves need some adjustments? Tps sensor?
I hang out in the C3 Forum so sorry if this is a common problem with a common solution.
Craig
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,490
Likes: 3,999
From: Cape Coral, Florida
Craig,
Does the car seem to run better at higher RPM ???...if so you might have a vacuum leak somewhere...do you have a scan tool ??...if so it would be a 2 minute diag !!...high long term fuel trims at idle that decrease at higher RPM...you could use propane or Brake Kleen to help identify the location...spray it around all vacuum hoses or after the MAF sensor...you will hear a definite change in idle !!!
Does the car seem to run better at higher RPM ???...if so you might have a vacuum leak somewhere...do you have a scan tool ??...if so it would be a 2 minute diag !!...high long term fuel trims at idle that decrease at higher RPM...you could use propane or Brake Kleen to help identify the location...spray it around all vacuum hoses or after the MAF sensor...you will hear a definite change in idle !!!
Thread Starter
Le Mans Master
Joined: Aug 2010
Posts: 5,339
Likes: 546
From: Central Texas
Originally Posted by rwobs777
Craig,
Does the car seem to run better at higher RPM ???...if so you might have a vacuum leak somewhere...do you have a scan tool ??...if so it would be a 2 minute diag !!...high long term fuel trims at idle that decrease at higher RPM...you could use propane or Brake Kleen to help identify the location...spray it around all vacuum hoses or after the MAF sensor...you will hear a definite change in idle !!!
Does the car seem to run better at higher RPM ???...if so you might have a vacuum leak somewhere...do you have a scan tool ??...if so it would be a 2 minute diag !!...high long term fuel trims at idle that decrease at higher RPM...you could use propane or Brake Kleen to help identify the location...spray it around all vacuum hoses or after the MAF sensor...you will hear a definite change in idle !!!
I'm ordering a scan tool this morning. Going to look at possibly having a vacuum leak until tool shows.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,490
Likes: 3,999
From: Cape Coral, Florida
What scan tool are you buying ??....don’t know how much you’re willing to spend but some “higher” end scan tools offer a lot more than your basic “code reader”...if it didn’t throw a MIL you haven’t reached the fuel trim percentage level that would set a P0171 or P0174 !!...a good visual inspection is all you might need to do !!
Thread Starter
Le Mans Master
Joined: Aug 2010
Posts: 5,339
Likes: 546
From: Central Texas
I'm thinking about purchasing this scan tool. My friend with the scanner is out of town for a week.
https://www.summitracing.com/parts/a.../submodel/base
https://www.summitracing.com/parts/a.../submodel/base
Last edited by Street Rat; Nov 12, 2018 at 10:01 AM. Reason: Add link
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,490
Likes: 3,999
From: Cape Coral, Florida
I'm thinking about purchasing this scan tool. My friend with the scanner is out of town for a week.
https://www.summitracing.com/parts/a.../submodel/base
https://www.summitracing.com/parts/a.../submodel/base
Thread Starter
Le Mans Master
Joined: Aug 2010
Posts: 5,339
Likes: 546
From: Central Texas
https://www.summitracing.com/parts/ino-5160
Burning Brakes
Joined: Jun 2015
Posts: 1,186
Likes: 306
From: Shelbyville Kentucky
Funny story. When I installed my FAST LSXR 102 manifold when I started the car for the first time. It ran like dog $*&t, sounded kind of like it has a huge cam in it. LOL
At first I though it will take the computer a few seconds to figure it out or maybe air in the fuel lines...
Nope, I forgot to hook the brake booster vacuum line back up. Huge effing vacuum leak!
At first I though it will take the computer a few seconds to figure it out or maybe air in the fuel lines...
Nope, I forgot to hook the brake booster vacuum line back up. Huge effing vacuum leak!
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Safety Car
Joined: May 2016
Posts: 4,639
Likes: 1,823
From: Erlanger, Kentucky
More than likely a vacuum leak. A simple test is to get some starting fluid and spray areas of the engine where there is a possibility of leaks. So any gasket mating surfaces such as the valve covers, valve cover bolts, PCV hoses, where the intake manifold mates to the heads, the brake booster hose, etc. You want to be careful not to spray the exhaust manifolds which could ignite the fluid. If you spray an area and the RPM's increase, you have found the area of the leak.
If I were you, I would get a set of new valve cover gaskets, valve cover bolt grommets, and a set of intake manifold gaskets. Maybe even a new PCV hose. Those will be the most likely culprits.
If I were you, I would get a set of new valve cover gaskets, valve cover bolt grommets, and a set of intake manifold gaskets. Maybe even a new PCV hose. Those will be the most likely culprits.
Thread Starter
Le Mans Master
Joined: Aug 2010
Posts: 5,339
Likes: 546
From: Central Texas
Got my scan tool and ran all of the diagnostic codes. I got a bunch of misc. codes that don't effect how the car runs. Nothing that would indicate a problem with the engine systems. So I'm pretty convinced it has to be a vacuum leak. I'll be checking for that today.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,490
Likes: 3,999
From: Cape Coral, Florida
what were the codes ????...what do your long term fuel trims (LTFT) and short terms look like at idle ??...if they are over 10% run the engine at 3-4000 RPM...if short terms and long terms decrease you have a vacuum leak for sure !!
Last edited by C5 Diag; Nov 16, 2018 at 09:51 AM.
Thread Starter
Le Mans Master
Joined: Aug 2010
Posts: 5,339
Likes: 546
From: Central Texas
Originally Posted by rwobs777
what were the codes ????...what do your long term fuel trims (LTFT) and short terms look like at idle ??...if they are over 10% run the engine at 3-4000 RPM...if short terms and long terms decrease you have a vacuum leak for sure !!
Now that I know what ltft and stft mean and what the values are. I should be able to run that test quite easily. I saw the values on the test tool but didn't know what they should be.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,490
Likes: 3,999
From: Cape Coral, Florida
Both long and short terms at 0 would be perfect but they are usually not !!!...keep us advised !!...as far as your new scan tool try to know what each data PID means...I wouldn’t worry about Mode 6 right now if you have it !!
Thread Starter
Le Mans Master
Joined: Aug 2010
Posts: 5,339
Likes: 546
From: Central Texas
I cleaned the throttle body. It was pretty gummed up. I guess if that was gunked up the MAF is too. I will clean that today. Just to make sure. It's the sensor attached to the air cleaner intake attachment? Correct?
I'll also be checking some scan information that was posted above.
I'll also be checking some scan information that was posted above.
