Misfirng...P0300
 

Hey guys,

About a month ago I had this problem with misfiring and I thought I had it fixed after I clean the MAF and the air filter. It ran fine for about a month and now it runs terrible. I have an 03 base with 150k miles. Before I go and spend money on plugs and new coilpacks I figured I would get your guy's input. Sometimes it will misfire right off start up and run terrible, but if I shut off the car and turn it back on, sometimes its fine, and sometimes it still terrible. I thought this was strange and had something to do with electrical maybe? I couldn't think of any reason why turning the car off and on again would fix the misfiring? I can't find any vaccum leaks or see any visible signs of a bad coilpack but I figured I would change the coilpacks and spark plugs first to give it a try. If anyone has any advice on what it could be, please let me know!

Thanks!

Spark plugs are cheap enough and at 150k if you haven't already replaced them once, it will be a good start in diagnosing the problem. How did you search for vacuum leaks?

I used a fog machine

could be coil packs going

UPDATE

Moved the car out of the garage today and it seemed to start up fine so I took it around the block to see if it would run fine. It was a little boggy and it seemed to misfire down the street, but later on it ran fine! This is so frustrating because it's so inconsistent. When this happens I have a really rough idle and a sort of thump at idle, but this is where a shut off and turn on would noramally fix the issue and it would run fine. Im confused lol. Buying plugs and looking into packs tomorrow...

Don't spend the money on plugs or coil packs

1. You need to diagnose the problem
2. Code p 0300 is random misfire (which is why it runs fine sometimes)
3. You NEED a compression test( this will give you answer that you seek)
4. Decisions ;

4a if your compression test shows that any of the 6 cylinders makes less than 150 psi then your rings are **** and you need rebuild (honing and rings replaced)

4b if the test shows 150 or above your ok but still low( 180 psi is oem spec) and then you need to test each coil pack with a ohm resistance meter to see if they are any good ( new ones from autozone cost 100 each) I would get some of c list( which is what I did and I got all 6 for 120).

4c. Now you need to check your spark plugs ,

Are they wet or dry?
Do they have the appropriate amount of gap?
Do they look burnt or dark in color?

If yes they need to be changed .


I am trying to save you money before you go and spend 300 dollars on a problem that you need to save close to 3k to fix