I recently had my check engine light come on in my 2005 Dodge Dakota. It has a 3.7 L V6 engine.

I used an OBDII reader on it and "PO300 -random misfire detected" was the code that came up.

What makes it somewhat more odd is my after market car alarm stopped working as soon as the CEL came on.

I first checked to see that my battery was still good. Go with the easiest one first. It seems it is fine, so it isn't due to lack of charge. What made me think it might be that is when I first start the truck, the engine runs low idle/rough for 20 45 seconds, then the idle becomes normal and I have no problems. While the idle is rough the CEL flashes and after it the issue goes away the light comes on solid.

I am looking at getting the plugs, coil packs and fuel filter replaced as it is likely due for such treatment.

Does anyone have any other theories as to what this may be, factoring in the check engine light behavior, the rough idle for the first 20 to 45 seconds then returning to normal and the car alarm ceasing to work when the problem arose?

I appreciate all input and ideas and advice!

 

how many miles on the truck?

 

Welcome to the forum. UNder what conditions did the CEL come on? Idling, cruising, etc. Is it running rough all the time? Have youn pulled the plugs and inspected them? Check the plug wires?

 

First off, Welcome to DF.

This might help you out a little bit.

P0300 Diagnostic code, Random misfire

 

Well, I'm always nervous when someone says they have an aftermarket alarm system

There may be a connection, or not. Or it may portend something bad in general. I'm always dubious as to where people attach these alarms to the various systems in the car, from ignition, to constant power, etc. Many installers are hacks IMHO, and this always comes back to bite everyone.

The rough idle is likely one or more sensors on the engine that are getting sketchy... I've gotten my idle back to 100% by systematically replacing the IAT, IAC, MAP, TPS, EGR, and the godforsaken Evap Purge Solenoid. Its improved each time, and with a fresh set of plugs and a battery disconnection here and there, it idles good as new (109K miles)

Early idle is most likely TPS/IAT/IAC getting pissed off. Hard to pinpoint which one, but they are reasonably cheap. The Coil packs are probably not bad, so its a pretty expensive swap if you're not sure. Usually, if a code is set in the computer OTHER than a random miss, it pinpoints which cylinder is having trouble. I would start with the IAC (idle air control), and see what happens.

It may seem like quite a few bits to replace, but they all interact. Some can cause vacuum leaks (IAC, Evap solenoid, MAP, EGR), while some start misreading the things they are supposed to read (TPS/IAT). They are all pretty cheap (I got mine from Rock Auto)

The random miss is another beast altogether. It could be an injector being cranky, or an oxygen sensor getting ready to go to the great exhaust system in the sky. But its more than likely one of these pesky sensors.

 

I just had codes for a misfire, replaced all the spark plugs and it's gone. If you've never replaced the plugs assume they've never been replaced. I'd go pick up some ac delco coppers, none of that fancy crap, and change them. It's $12 and has a really good chance of curing the issue.

 

Not sure if the alarm system will like it, but you can always unplug the battery overnight, that should reset the truck and clear the code. If the code comes back, I would dig deeper.

I only say this, because its just a random code, not specific. Coils are rare to go bad, but I would check those plugs, they are not that bad to get to.

 

The only time ive seen this code is when the catalytic converters are going out. Have you had egr problems? what about engine oil dissapearing? A mechanic can check the catalyst temps when at temperature.

If it were the plugs a single cylinder would misfire. Coils have thier own obd2 dianostic code followed by a misfire code for the effected cylinder. The alarm is a different system and usually present as a no start.

 

I got this code after I washed my engine and moisture condensed around the insulators on some of my coil packs. I don't think it was direct water spray that got down inside, but rather the humidity was so high that it allowed moisture to condense inside the cavity. I removed the coil packs, cleaned and dryed them, and replaced the spark plugs. All went away.

 

Welcome to DF Mr. Hell.

Seems like the guys have you on the right track.




You newb Since when did we get plug wires on our Daks