P0300 Code..
Thread Starter
Drifting
Joined: Jan 2008
Posts: 1,752
Likes: 62
From: New Madison Ohio
Check Engine Light Flashing..P0300 Code..
Driving today and parked to eat no troubles. Got ready to leave the car had a rough idle, running sluggish or not hitting on all cylinders. The check engine light did come on and I ran a diagnostic check while driving and got the P0300 Code. I know it is an engine misfire according to what I read, but any direction to help solve the problem would be helpful. I really don't want to take it to a dealership to have it checked out if possible. Basically the car runs like crap.
Last edited by DA1984VETTE; Jul 14, 2016 at 11:39 AM.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Without knowing the age and condition of the entire secondary ignition system (plugs & wires) I would have to recommend that you start there!
Install NEW GM Irridium sparkplugs gapped at 0.040" and purchase and install some new GM Performance RED Wires!
The above recommended replacement parts are the BEST BANG FOR THE BUCK and will last for another 75,000 miles!
You can also just inspect what you have. Look for loose wires on the plugs and coil towers. They tend to pop off sometimes. Also make sure that the wires are not damaged insulation wise. If there an OEM wire, You can OHM out the wires. The OEM wires should measure approx. 250 ohms to 750 ohms. OEM Wires reading in the high 1000s ohm range are BAD.
Start there and let us know what you have..
Gene Culley (Forum Sponsor) has the wires for around $65.
Bill
Bill
Install NEW GM Irridium sparkplugs gapped at 0.040" and purchase and install some new GM Performance RED Wires!
The above recommended replacement parts are the BEST BANG FOR THE BUCK and will last for another 75,000 miles!
You can also just inspect what you have. Look for loose wires on the plugs and coil towers. They tend to pop off sometimes. Also make sure that the wires are not damaged insulation wise. If there an OEM wire, You can OHM out the wires. The OEM wires should measure approx. 250 ohms to 750 ohms. OEM Wires reading in the high 1000s ohm range are BAD.
Start there and let us know what you have..
Gene Culley (Forum Sponsor) has the wires for around $65.
Bill
Bill
Race Director
Joined: Mar 2010
Posts: 15,996
Likes: 824
Driving today and parked to eat no troubles. Got ready to leave the car had a rough idle, running sluggish or not hitting on all cylinders. The check engine light did come on and I ran a diagnostic check while driving and got the P0300 Code. I know it is an engine misfire according to what I read, but any direction to help solve the problem would be helpful. I really don't want to take it to a dealership to have it checked out if possible. Basically the car runs like crap.
I am sorry to hear you’re experiencing these concerns with your Corvette and understand how this may be frustrating. I see that you are seeking advice from other forum members, however, please don’t hesitate to send us a private message if you would like to visit your dealership. We would be happy to provide an additional layer of support during that process!
Best,
Julie C
Chevrolet Customer Care
Thread Starter
Drifting
Joined: Jan 2008
Posts: 1,752
Likes: 62
From: New Madison Ohio
Without knowing the age and condition of the entire secondary ignition system (plugs & wires) I would have to recommend that you start there!
Install NEW GM Irridium sparkplugs gapped at 0.040" and purchase and install some new GM Performance RED Wires!
The above recommended replacement parts are the BEST BANG FOR THE BUCK and will last for another 75,000 miles!
You can also just inspect what you have. Look for loose wires on the plugs and coil towers. They tend to pop off sometimes. Also make sure that the wires are not damaged insulation wise. If there an OEM wire, You can OHM out the wires. The OEM wires should measure approx. 250 ohms to 750 ohms. OEM Wires reading in the high 1000s ohm range are BAD.
Start there and let us know what you have..
Gene Culley (Forum Sponsor) has the wires for around $65.
Bill
Bill
Install NEW GM Irridium sparkplugs gapped at 0.040" and purchase and install some new GM Performance RED Wires!
The above recommended replacement parts are the BEST BANG FOR THE BUCK and will last for another 75,000 miles!
You can also just inspect what you have. Look for loose wires on the plugs and coil towers. They tend to pop off sometimes. Also make sure that the wires are not damaged insulation wise. If there an OEM wire, You can OHM out the wires. The OEM wires should measure approx. 250 ohms to 750 ohms. OEM Wires reading in the high 1000s ohm range are BAD.
Start there and let us know what you have..
Gene Culley (Forum Sponsor) has the wires for around $65.
Bill
Bill
Drifting
Joined: Jul 2015
Posts: 1,844
Likes: 375
From: San Jose, CA
I believe that 0.040 is recommended for most cars. They used to come with 0.060 but it was too big a gap and some cars did not run smoothly.
If it still runs bad, I'd do all the other basics:
- Clean / replace engine air filter
- Replace fuel filter
- Run techron concentrate through the fuel system
- Clean MAF sensor
- Replace PCV valve
- Check that the idle air controller works by tapping it as it runs and observing whether there is any change in idle speed
- Make sure your AC is off
- Clean your throttle body
- Look/listen for any vacuum leaks (also, with the car idling and parking brake on, does the idle change as you depress the brakes? this is indicative of vacuum leak or failing/failed brake booster)
This is always a good place to start for rough idle / rough running situations.
If it still runs bad, I'd do all the other basics:
- Clean / replace engine air filter
- Replace fuel filter
- Run techron concentrate through the fuel system
- Clean MAF sensor
- Replace PCV valve
- Check that the idle air controller works by tapping it as it runs and observing whether there is any change in idle speed
- Make sure your AC is off
- Clean your throttle body
- Look/listen for any vacuum leaks (also, with the car idling and parking brake on, does the idle change as you depress the brakes? this is indicative of vacuum leak or failing/failed brake booster)
This is always a good place to start for rough idle / rough running situations.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
I believe that 0.040 is recommended for most cars. They used to come with 0.060 but it was too big a gap and some cars did not run smoothly.
If it still runs bad, I'd do all the other basics:
- Clean / replace engine air filter
- Replace fuel filter
- Run techron concentrate through the fuel system
- Clean MAF sensor
- Replace PCV valve
- Check that the idle air controller works by tapping it as it runs and observing whether there is any change in idle speed
- Make sure your AC is off
- Clean your throttle body
- Look/listen for any vacuum leaks (also, with the car idling and parking brake on, does the idle change as you depress the brakes? this is indicative of vacuum leak or failing/failed brake booster)
This is always a good place to start for rough idle / rough running situations.
If it still runs bad, I'd do all the other basics:
- Clean / replace engine air filter
- Replace fuel filter
- Run techron concentrate through the fuel system
- Clean MAF sensor
- Replace PCV valve
- Check that the idle air controller works by tapping it as it runs and observing whether there is any change in idle speed
- Make sure your AC is off
- Clean your throttle body
- Look/listen for any vacuum leaks (also, with the car idling and parking brake on, does the idle change as you depress the brakes? this is indicative of vacuum leak or failing/failed brake booster)
This is always a good place to start for rough idle / rough running situations.
Go 0.040
! 
EXACTLY!Bill
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
I agree plugs and wires would be my 1st and most common fix------
That being said if that does not cure the misfire there are other things that can cause a P0300 code---- A faulty injector would throw a whole new code so I would not suspect injectors However I have seen cars especially those approaching 10 years of age where a clogged or bad CAT will throw a misfire code---Typically when a cat fails the car will feel extremely down on power So if the plugs and wires don't cure it---Have your cats checked for backpressure at most any reputable muffler shop
That being said if that does not cure the misfire there are other things that can cause a P0300 code---- A faulty injector would throw a whole new code so I would not suspect injectors However I have seen cars especially those approaching 10 years of age where a clogged or bad CAT will throw a misfire code---Typically when a cat fails the car will feel extremely down on power So if the plugs and wires don't cure it---Have your cats checked for backpressure at most any reputable muffler shop
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
So it ran fine until you came out of a restaurant and then it ran bad? Did it happen immediately or was it a mile or two down the road? Had you recently bought fuel?
If it were mine, I think I might disconnect the battery to clear the fuel trims and then try again and see what happens.
If it were mine, I think I might disconnect the battery to clear the fuel trims and then try again and see what happens.
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Thread Starter
Drifting
Joined: Jan 2008
Posts: 1,752
Likes: 62
From: New Madison Ohio
So it ran fine until you came out of a restaurant and then it ran bad? Did it happen immediately or was it a mile or two down the road? Had you recently bought fuel?
If it were mine, I think I might disconnect the battery to clear the fuel trims and then try again and see what happens.
If it were mine, I think I might disconnect the battery to clear the fuel trims and then try again and see what happens.
Thread Starter
Drifting
Joined: Jan 2008
Posts: 1,752
Likes: 62
From: New Madison Ohio
I believe that 0.040 is recommended for most cars. They used to come with 0.060 but it was too big a gap and some cars did not run smoothly.
If it still runs bad, I'd do all the other basics:
- Clean / replace engine air filter
- Replace fuel filter
- Run techron concentrate through the fuel system
- Clean MAF sensor
- Replace PCV valve
- Check that the idle air controller works by tapping it as it runs and observing whether there is any change in idle speed
- Make sure your AC is off
- Clean your throttle body
- Look/listen for any vacuum leaks (also, with the car idling and parking brake on, does the idle change as you depress the brakes? this is indicative of vacuum leak or failing/failed brake booster)
This is always a good place to start for rough idle / rough running situations.
If it still runs bad, I'd do all the other basics:
- Clean / replace engine air filter
- Replace fuel filter
- Run techron concentrate through the fuel system
- Clean MAF sensor
- Replace PCV valve
- Check that the idle air controller works by tapping it as it runs and observing whether there is any change in idle speed
- Make sure your AC is off
- Clean your throttle body
- Look/listen for any vacuum leaks (also, with the car idling and parking brake on, does the idle change as you depress the brakes? this is indicative of vacuum leak or failing/failed brake booster)
This is always a good place to start for rough idle / rough running situations.
Thread Starter
Drifting
Joined: Jan 2008
Posts: 1,752
Likes: 62
From: New Madison Ohio
Put in new plugs today gapped at .040 still no change. No new codes are showing up. It acts like it is not getting enough fuel, that is just my opinion. It just feels like I am towing a load and doesn't have enough power to pull it. At my wits end with it...
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
IDLE AIR CONTROLER ????????????????????????? Your LS engine does NOT have an idle air controller. The PCM adjust the Throttle blade to control idle.
Pull off ONE plug wire at a time and see what that does to the engine idle.
If you disconnect a wire and it does little or nothing, that cylinder is NOT working properly.
The ones that cause the engine to falter and run WORSE are taking most of the load.
Pull off ONE plug wire at a time and see what that does to the engine idle.
If you disconnect a wire and it does little or nothing, that cylinder is NOT working properly.
The ones that cause the engine to falter and run WORSE are taking most of the load.
Thread Starter
Drifting
Joined: Jan 2008
Posts: 1,752
Likes: 62
From: New Madison Ohio
Thanks for all the help and suggestions guys I really do appreciate it. I haven't been able to drive it for a couple of weeks because of the problem or problems so I just gave up and it's now at Bud's (Forum Sponsor) in Celina to be checked out. Again thanks for all the help..
Thread Starter
Drifting
Joined: Jan 2008
Posts: 1,752
Likes: 62
From: New Madison Ohio
Just heard from Bud's about my car. It seems there was no compression on #2 cylinder. They found the intake valve spring was broken. They said the valve spring is not a GM spring and wanted a little info on my car. I advised them the guy I bought it from said it had the Z06 hot cam in it. I asked him why the change was made and he advised it was done before I got it. So I would "assume" that they changed the valve springs when they did the cam swap. So they are going to do more research on the spring to see what kind it is and get it replaced. Hopefully this fixes the problem..
Drifting
Joined: Jul 2015
Posts: 1,844
Likes: 375
From: San Jose, CA
Damn, no compression on a cylinder, that will do it. Good luck!
If one spring is broken... being the slightly paranoid person I am, I'd probably just replace all of them instead of just the one.
If one spring is broken... being the slightly paranoid person I am, I'd probably just replace all of them instead of just the one.
Instructor
Joined: May 2010
Posts: 233
Likes: 1
From: San Benito TEXAS
U can check which plugs are firing with a timing light
by clipping the holder to each wire and pressing the timing light button each time it fires the light will flash if it doesnt flash check wire and plugs on this cylinder.....
by clipping the holder to each wire and pressing the timing light button each time it fires the light will flash if it doesnt flash check wire and plugs on this cylinder.....
Thread Starter
Drifting
Joined: Jan 2008
Posts: 1,752
Likes: 62
From: New Madison Ohio
I got her back today and all is well. She runs like she used to...
I want to thank everyone for the suggestions as they were much appreciated and I did try most of the suggestions before getting fed up and took her to Bud's. If this happens again and I DON'T drop a valve I will as someone suggested go ahead and put all new springs in. Funds were a little tight this time around to do that. Again a big THANK YOU to everyone who responded...
I want to thank everyone for the suggestions as they were much appreciated and I did try most of the suggestions before getting fed up and took her to Bud's. If this happens again and I DON'T drop a valve I will as someone suggested go ahead and put all new springs in. Funds were a little tight this time around to do that. Again a big THANK YOU to everyone who responded...
