The dreaded p0303, now p0300 DTC code
10-23-2015 | 02:56 PM
#1
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From: Tacoma, WA
The dreaded p0303, now p0300 DTC code
Hey Guys,
So, having some serious issues. Car is 2006 Supercharged, approximately 136,000 miles. Purchased brand new, been a great runner up until recently. At first oil change, flushed and ran on premium oil filters and full synthetic for life. Half of the cars mileage is exclusively highway. Car has not been modded. Recently, bought a new car and handed this over to my son, but title still in my name and issues still mine to fix at this point, as I'm the only one with income.
Only problem I noticed prior to handing it over to him, was occasional idle surge at stops. Was never anything serious, but would surge 300 to 500 rpms upon stopping, and only intermittently. Fast forward to about 2 months ago. While driving home my son got a flashing engine light and when he came to a stop, idle surging and car died. He managed to baby it home. Took it to O'Reilly's. I notice the idle surged at start up, but will eventually settle down when left alone, but also running a bit rough. Upon driving it to O'reilly's, stayed running as long as it was moving, but as soon as you put your foot on the clutch idle began to surge dramatically, and unless you kept giving it fuel, it would die. If I slow with the brakes first while walking it down through the gears I can manage to keep it pretty much running upon stopping with alot less surge, if any. I am a driver by profession, but I'm only a layman when it comes to mechanicals, so please bear with me.
So, first code pulled was a p0303 (cylinder 3 misfire). Replaced spark plugs, and cylinder 3 coil. Plugs had white oxidation and signs of running lean, also cylinder 3 plug was missing most of the ground electrode (the little L-shaped thing at the bottom for layman). Plugs are AC Delco, and my son bought the coil online.
Immediately when problems began, I began trolling the internet and doing as much research as possible on this issue. Saw on a couple of forums that the coil purchased online might be suspect and better to get OEM dealer coils. At any rate, after replacing plugs and one coil, reset the car and tried again. Still having issue, except then upon checking the codes it changed to a p0300, random multiple misfire. Also, noticed at one point it smelled like it was running rich and had some exhaust smoke indicating it was running rich. The exhaust smell was only evident for a small amount of time and only saw the smoke once, this was after the first set of plugs and the the cylinder 3 coil were changed, and it only happened once, but was a little confusing, as the plugs showed evidence that the car was running lean.
So, fast forward to two weeks ago. Cleaned out K and N air filter, changed fuel filter, replaced all four coils with dealer purchased units. No dice, still pulling same code, seems to be running a little better though and engine light is now intermittent. However, even after reset, same code is still showing. Got a spark tester and going to pull each plug one at a time (haven't yet), inspect it really good, check the gap again, replace and put the spark tester on it (tester might shed some light on whether its a fuel or ignition issue specifically). Believe in it, hooked it up before restarting after fuel filter replacement, but before resetting computer. Car wouldn't start yet and tester pointed to a fuel issue. Turns out we accidentally put the fuel pump fuse in the wrong spot when plugging it back in and needed to reset the computer. Once we did that it started right up.
At any rate, I've been doing tons of research. I don't have a bunch of money laying around so, need to work through this one step at a time starting with the least expensive repairs. My next steps will be to clean the air intake and replace seals/gaskets, clean the throttle body thoroughly, check the fuel rail for air leaks, and check the various wiring harnesses and grounds suggested in another place (and if this fails, spark plugs are relatively cheap, so may pick up four more at the dealership just to be on the safe side). If this doesn't fix the issue, and there is evidence of air leaking at the rail, I'm going to take it in and have the shop check the fuel injectors, and also check the timing to rule out any problems with the timing chain. If it turns out an injector is bad, I'd rather replace the o-rings during the injector replacement, so we're not doing it twice. Next steps would be various sensors (MAF, O2 sensors, MAP, Cam sensor.......don't think it would be Crank sensor or else would it even start?), then someone mentioned a cannister purge solenoid. After that check the Cat, and of course if the shop says it points to injectors or timing chain, those would be next in line too. Hopefully, the issue will be resolved long before it comes down to the later items on the list. Am I forgetting anything? Any suggestions? Please let me know. Also, when we do get it actually fixed I will post a follow up to explain what actually worked. I noticed that on some of the threads, the actual resolution was never posted, which may have helped someone else with this issue. Thank you for letting me ramble.
So, having some serious issues. Car is 2006 Supercharged, approximately 136,000 miles. Purchased brand new, been a great runner up until recently. At first oil change, flushed and ran on premium oil filters and full synthetic for life. Half of the cars mileage is exclusively highway. Car has not been modded. Recently, bought a new car and handed this over to my son, but title still in my name and issues still mine to fix at this point, as I'm the only one with income.
Only problem I noticed prior to handing it over to him, was occasional idle surge at stops. Was never anything serious, but would surge 300 to 500 rpms upon stopping, and only intermittently. Fast forward to about 2 months ago. While driving home my son got a flashing engine light and when he came to a stop, idle surging and car died. He managed to baby it home. Took it to O'Reilly's. I notice the idle surged at start up, but will eventually settle down when left alone, but also running a bit rough. Upon driving it to O'reilly's, stayed running as long as it was moving, but as soon as you put your foot on the clutch idle began to surge dramatically, and unless you kept giving it fuel, it would die. If I slow with the brakes first while walking it down through the gears I can manage to keep it pretty much running upon stopping with alot less surge, if any. I am a driver by profession, but I'm only a layman when it comes to mechanicals, so please bear with me.
So, first code pulled was a p0303 (cylinder 3 misfire). Replaced spark plugs, and cylinder 3 coil. Plugs had white oxidation and signs of running lean, also cylinder 3 plug was missing most of the ground electrode (the little L-shaped thing at the bottom for layman). Plugs are AC Delco, and my son bought the coil online.
Immediately when problems began, I began trolling the internet and doing as much research as possible on this issue. Saw on a couple of forums that the coil purchased online might be suspect and better to get OEM dealer coils. At any rate, after replacing plugs and one coil, reset the car and tried again. Still having issue, except then upon checking the codes it changed to a p0300, random multiple misfire. Also, noticed at one point it smelled like it was running rich and had some exhaust smoke indicating it was running rich. The exhaust smell was only evident for a small amount of time and only saw the smoke once, this was after the first set of plugs and the the cylinder 3 coil were changed, and it only happened once, but was a little confusing, as the plugs showed evidence that the car was running lean.
So, fast forward to two weeks ago. Cleaned out K and N air filter, changed fuel filter, replaced all four coils with dealer purchased units. No dice, still pulling same code, seems to be running a little better though and engine light is now intermittent. However, even after reset, same code is still showing. Got a spark tester and going to pull each plug one at a time (haven't yet), inspect it really good, check the gap again, replace and put the spark tester on it (tester might shed some light on whether its a fuel or ignition issue specifically). Believe in it, hooked it up before restarting after fuel filter replacement, but before resetting computer. Car wouldn't start yet and tester pointed to a fuel issue. Turns out we accidentally put the fuel pump fuse in the wrong spot when plugging it back in and needed to reset the computer. Once we did that it started right up.
At any rate, I've been doing tons of research. I don't have a bunch of money laying around so, need to work through this one step at a time starting with the least expensive repairs. My next steps will be to clean the air intake and replace seals/gaskets, clean the throttle body thoroughly, check the fuel rail for air leaks, and check the various wiring harnesses and grounds suggested in another place (and if this fails, spark plugs are relatively cheap, so may pick up four more at the dealership just to be on the safe side). If this doesn't fix the issue, and there is evidence of air leaking at the rail, I'm going to take it in and have the shop check the fuel injectors, and also check the timing to rule out any problems with the timing chain. If it turns out an injector is bad, I'd rather replace the o-rings during the injector replacement, so we're not doing it twice. Next steps would be various sensors (MAF, O2 sensors, MAP, Cam sensor.......don't think it would be Crank sensor or else would it even start?), then someone mentioned a cannister purge solenoid. After that check the Cat, and of course if the shop says it points to injectors or timing chain, those would be next in line too. Hopefully, the issue will be resolved long before it comes down to the later items on the list. Am I forgetting anything? Any suggestions? Please let me know. Also, when we do get it actually fixed I will post a follow up to explain what actually worked. I noticed that on some of the threads, the actual resolution was never posted, which may have helped someone else with this issue. Thank you for letting me ramble.
Last edited by horsinround1974s; 10-23-2015 at 08:24 PM.
10-23-2015 | 08:09 PM
#2
This is quite the through thread man, it is a bit hard to read though as it's a rather large wall of text on my screen. Minor request, could you break it up into paragraphs? I'm more than happy to help diagnose anything you're having issues with. 
It sounds like you either have a vacuum leak, need to clean the MAF, or run some injector cleaner through her. Get a bottle of the Concentrated Chevron Techron stuff, usually helps a bit and it's cheap. Any codes other than the P0303 and P0300?
It sounds like you either have a vacuum leak, need to clean the MAF, or run some injector cleaner through her. Get a bottle of the Concentrated Chevron Techron stuff, usually helps a bit and it's cheap. Any codes other than the P0303 and P0300?
Last edited by YelloEye; 10-23-2015 at 08:16 PM.
10-23-2015 | 08:28 PM
#4
ModeratorJoined: 04-18-14
Posts: 16,465
Likes: 603
From: El Paso, TX
I think he means get to the point faster and more people will chime in, it is a long read. Not trying to be a Jerk or anything just trying to help
What you could try and you mentioned is cleaning the tb
What you could try and you mentioned is cleaning the tb
10-23-2015 | 08:41 PM
#5
Nah, I just mean't to space it out. That's perfect, much easier to read. Thank you.
I'm still leaning towards it being a dirty/bad MAF or a minor vacuum leak, but it could be fuel related.
If you wanted to join us out at Griot's garage on the 7th around 8am I'd be happy to take a look, there's a few of us that meet up on the first Saturday of the month when Griot's is having their car gatherings. Looks like next month is German cars so might see something rare in their showroom. Events Calendar - Griot's Garage
I'm still leaning towards it being a dirty/bad MAF or a minor vacuum leak, but it could be fuel related.
If you wanted to join us out at Griot's garage on the 7th around 8am I'd be happy to take a look, there's a few of us that meet up on the first Saturday of the month when Griot's is having their car gatherings. Looks like next month is German cars so might see something rare in their showroom. Events Calendar - Griot's Garage
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