P0307 mystery

Discussion in 'GM Powertrain' started by Vonderbach, Nov 19, 2012.

  1. Vonderbach

    Vonderbach New Member

    About a month ago I started popping codes on my 2007 Chevy Avalanche (LT, 5.3 Vortec 5800 LMG Engine.) I did my research and foudn that, as suspected, I was getting a misfire on cyl. 7. Knowing that there are a host of problems that could contrinute, I dicided to eliminate the easiest one first, which was long over due anyway. I replaced the plugs and wires, as at 160,000 miles they had never been replaced previously. (shame on me, I know.) After replacing the plugs/wires and resetting the codes with my handy doodad, the misfire (rough idle, occasional engine jump, etc) was still present.....BUT NO ENGINE CODES OR LIGHTS?

    So now I'm wondering what to do. I hate to take it to the dealership and have them run off with my wallet, but I can't figure out what is wrong without an error code to eliminate it. I thought about disconnecting cyl 7 and seeing if the rough idle continued, but it's so random and slight that I'm afraid I won't be able to tell.

    A few details:

    • Rough engine idle occurs after warming up. A cold engine runs nicely.

    • A few other codes were presented at the same time, but I didn't write them down, so I can't recall exactly what they were. One had to do with the fuel vapor solenoid (P0443, P0446, etc.) I bought the solenoid itself and was ready to replace it, but since the code is gone now...I have no idea if it's still an issue. Can this cause a rough idle (i.e. misfire?) The other code was related to the P0307 but I can't recall what it was.

    Any thoughts, ideas, suggestions, etc?
  2. Curky

    Curky Epic Member 5+ Years 1000 Posts

    I can’t help but do this. Type P0307 in the search engine in the top right of the page. I did it and there are three other threads that might help.
  3. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    What brand plugs did you put in? From what I have seen some brands of plugs don't always "agree" with the GM ignition system. I always use the recommended AC Delco plug. I got talked into some Autolite plugs by the guys at autozone one time. I put them in my 02 silverado and it idled like crap. I swapped them out with AC plugs and the idle smoothed out right away. Also, many of the new Ac plugs do not recommend adjusting the gap as you will damage the electrode when doing so. Is it possible that you got some dirt on the tip of the plug when installing? Have you cleaned your MAF sensor with MAF cleaner yet? Have you cleaned the throttle body? The MAF and throttle body being dirty can lead to a rough idle. If you are no longer getting a code you may have solved the misfire by replacing the plugs and wires.
  4. Vonderbach

    Vonderbach New Member

    I've been Googling the heck out of this site and others with that code ID, and it got me this far, but I'm stuck at this point now. But thank you for the head up on those links, you never know what I may have missed. Thanks!

    I got the AC Delco Irridium which is what was reccommened. I have not cleaned the MAF or throttle body yet, but wouldn't these affect more than just cyl 7? Again, I'm assuming it's limited to cyl 7 since that was the original error code which was provided. Is cleaning these two items very difficult? I have never attempted it.

    I did clean the engine before replacing the plugs using compressed air, so I think that should be fine.

    I think what's really got me confused is the rough idle with absolutely no indicators of a problem. Does CHevy have a time limit or a cycle where it will wait to turn on the check engine light if a problem has been cleared from the memory?
  5. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    If there is no code then I would not assume it is #7 any longer. To clean the MAF sensor you need to buy a can of MAF cleaner. Pull your intake tube off. Take the MAF sensor out. Spray it down, let it dry and reinstall it. The throttle body is pretty easy also. Buy a can Of throttle body cleaner. (don't use brake clean or carb cleaner, it can take the protective coating off of the inside of the Throttle body) Take you air intake tube off. spray the cleaner into the throttle body, use a tooth brush and scrub the inside. Use your finger to open the plate and clean behind it. Clean the front and backside of the plate. Everything should be nice and shiny when you are done. I use a rag to wipe up the gunk while I clean it. Just make sure that you don't get it caught on anything or leave any pieces inside your throttle body. Reassemble it and start your truck. It may run like crap for a few seconds, because all the cleaner and dirt is being burned off. But, after a few seconds it will smooth out. Another thing that you might want to do is suck some Sea foam into the intake thru the brake booster vacuum hose. Search the site and you should find a few threads about how to do it. I did that in my 03 yukon xl, it stopped ticking and the idle smoothed out. Another question is, have you cleaned the egr valve? Sometimes the valve and the pipe leading to it become partly clogged and cause a rough idle. Search that also and you will find threads discussing how to clean them, the gasket is $4 at autozone. If you clean all three of the above things it should take you less then 30 minutes. Personally I would clean the things listed and see if it smooths the idle out, 30 minutes and $12 is worth it in my opinion. If it does not smooth it out then at least you can eliminate them from the equation
    Last edited: Nov 19, 2012
  6. Vonderbach

    Vonderbach New Member

    Thank you for that very detailed TO-DO list! I'm going to get those items you mentioned and take care of business this holiday weekend and see what happens. I'll report back with success or frustration, whichever comes my way.

    Thanks again! :)
  7. Vonderbach

    Vonderbach New Member

    Update! So a couple codes came back after about 60-70 miles, P0449 and P0455, both are EVAP solenoid code and I bought the assembly so I should be all set as far as those codes are concerned.

    However, I am still getting a rough idle. I cleaned the MAF sensor as you suggested, haven't done the throttle body yet (too late last night.) But I am wondering if thre is ANY chance that the EVAP system is causing poor ventilation that might cause rough idle. The stealership told me that there was no relation to these system, but I know that isn't the case, as the EVAP helps to keep proper pressure in the fuel tank....so I'm wondering if perhaps a fauly EVAP solenoid could potentially cause an improper fuel mixture to the cylinders?

    I know I'm reaching, and I'll find out for sure tonight, but I wanted to know if anyone here had any such experience?


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