2003 Gen 3.5 with service engine soon code: P0300

[Offroadmuch]

Any advice? Says cylinder 1 misfired and other misc possible issues.

 

[nwoods]

Well, hopefully its not like my Gen 2.5, but there is a whole host of things it could be. Here is a good site to define the codes, possible sources, symptoms, etc..
http://www.autocodes.com/p0300_mitsubishi.html

If you can pull the spark plug, it might tell you a lot.

 

[Offroadmuch]

Thank you nwoods. A few weeks ago I did a complete coolant flush and put in a new thermostat. I also cleaned my K&N airfilter. Everything was perfect and now I am getting the "service engine soon" every now and then. I got the code read as posted above for free. They want $100 for a detailed diagnostic. I might wait until I do the timing belt. It seems to run perfecly with just a hint of a slightly rough idle. I will probably theow in 6 new iridium plugs.

 

[Inyo_man]

It's strange the shop told you that cylinder 1 was misfiring...

P0300: Random/multiple misfire detected

If it was only cylinder 1 that was misfiring, then the code would have been P0301.

You mentioned replacing the sparks...
When was the last time the sparks and wires were replaced?

 

[DSouth]

While you're replacing plugs test the ignition coils too.....but, that code could mean a lot of things. Before you go replacing things get a second opinion/read of codes. I prefer to spend the money to take it to the dealer so they can use the proper MUTII code reader, but Autozone will do it too.

 

[Offroadmuch]

I saw cylinder one misfire on the paperwork. Not sure on plug and plug wire replacement. Very few maintenance records when I purchased it earlier this year, April... So I am guessing original plugs and wires. It has 159,625 or so for miles.

 

[Salonika]

I get a random misfire every few months.....I just clear the code and forget about it. If it was more frequent I might try harder to fix it, but my truck is 20 years old and to me that is to be expected.

 

[TheMole]

How long have you had your k&n? Any of the oil get in the maf?

 

[Offroadmuch]

I think it might be just random, however the "service engine soon" stayed on much longer this time. The K&N is old and probably been in there a very long time. I cleaned it a few months ago and re-oiled per instructions and how I used to do it on my old 1986 Toyota. That was all good to go but I will look inside the air box again when I get home. I did check it and it was spotless. Can moving my air box around cause this? I saw that leaks etc. on the air intake is listed as potential causes of the problem for the p0300 code.

On a slightly different note... If my plugs are very old can I expect any small performance improvement by a new set of Iridiums? And as someone mentioned about coils, how can I tell if they are bad?

 

[DSouth]

Grab the FSM PDF's and follow the instructions. It's essentially just testing resistance of the coil pack with a digital multimeter(DMM). As long as your coils are within spec you can rule them out. I'd do a visual inspection of the plug tubes as well and clean out any oil or moisture. Put some dielectric grease on the plug connectors too while you're at it(if you have it).

I'm in Orange County as well, where abouts are you located?

 

[Offroadmuch]

Dsouth i sent a pm. What are you driving?

 

[DSouth]

2003 Monty Limited w/173k miles. Check the plugs for sure, and since you have to pull the coils to check the plugs, check them too. It's cheap insurance and not too hard to do. The hardest ones are the drivers side ones as they are hard to access due to the intake manifold. That said, it really isn't too hard to pull the intake manifold either, just take your time and lots of pics. I just went through this on mine looking for a stuck lash adjuster. I ended up pulling the intake, valve covers and all the lash adjusters, replacing the plugs and valve cover seals. If you are moderately mechanically inclined it is all doable. I wouldn't wait on the plugs if you don't know their history.