rough idle

Shot in the dark.

What about this puppy? And even clean the hole it sits in.

https://shop.advanceautoparts.com/p/bwd-idle-air-control-valve-21755p/3488500-P?searchTerm=iac

The Medic

I would not think this would be, since I replaced not to long ago, it has not been driven a whole lot so a good chance it being carbon up is slim to none. I would not think this would cause a p0300. The EGR valve was replaced a few summers ago. Slim chance this would be opening too or leaking off since it does not get driven that much. Sounds like a project for Red jacket to blow up! Lol

Okay, so you start it and it runs fine until it gets warm, then it runs rough and sets the P0300 code?

Low fuel pressure, bad fuel pressure regulator, Crappy gas from setting, partially blocked exhaust.

Got a scan tool that can read live misfire data? Which cylinders are throwing the most misfires? What is the battery voltage? Good ground and battery connections?

I do not think it is bad gas. My son in law has been driving it for the past month. Still popping the code. I did pop a o2 sensor code bank one. Which this is weird due to its brand new. I still holding on a fuel delivery issue. I need to check fuel pressure and injector functions. Fuel regulator is brand new the old one went bad last year. I am weighing in on dirty injectors.

Run the wiring for the O2. If it is showing a code it's possible it is shorted/open and that is causing the PCM to alter the mix enough that it's giving you a lean mix.

I will Check this once I get the Van back. It’s on loan right now. On that same note! I came across another discovery in my investigations on another Van that I just picked up. This Van runs well but was throwing a p0303. I gave it a tune up and replaced with OEM parts. The code went away and came back. Did all my other test to check spark, air leaks and sorforth. Last night I pulled the # 3 plug just to see how it was burning. Keep in mind the plugs have only been in for two weeks. The number three plug already had a crack in the porcelain. Come to find out this is caused by lean conditions due to dirty fuel injectors and causing the plug to ground out. Im going to clean the fuel systems on both Vans and replace plugs again. I believe this will take care of the issues. So if someone tells you that dirty fuel injectors won’t cause a p0300 they are wrong! If you have two to three injectors that are not working correctly that’s going to throw ap0300 due to lean conditions. So if anyone else is having this same issue check the plugs just above the Electroid for cracks. I’ll let you know how this turns out. Thanks for all your help.

Great observation! yes a bad fuel injector witht cause the cylinder to misfire causing the codes. Here is a guide that will how you how to test the injector to see if that is the problem.

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Please let us know what happens.

Cheers, Ken

Sorry Ken for such a long delay! Just found all of these in my Junk box. On the Chevrolet I have not messed with it yet just waiting for it to blow up! But For the Chrysler Town and Country that is another story. Let me fill you in a little on the Chrysler. Started out as a P0303. Changed plugs and went away for about 300 miles and code came back. Checked plugs again #3 had carbon tracks a little confused at the moment since these only had 300 miles. Shortly after this I started having long crank time and strong gas smell once started. Dug a little deeper! #3 plug had a strong gas odor on the end of the electrode. HMM! #3 injector leaking off flooding cylinder out! On top of this I started getting P0300, about three plugs had carbon tracks, about 2,000 miles on pugs now. Went to the junk yard pulled six injectors, cleaned injectors, new o-rings all around, new plugs. No more long crank time and runs like a champ. Long story short a P0300 can be caused by bad fuel injectors and some people say that bad fuel injectors will not cause a P0300. Lean fuel trims cause higher heat which leads to plug failure and can cause severe engine damage.

Did you ever get the problem fixed for the rough idle?

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Cheers, Ken

Anything in the cylinder can cause a misfire, the PCM only looks at the rotational speed on that vehicle. It needs to be within a certain percentage to be a "good" cylinder. Anything that causes a lower number triggers the misfire code. Rich or lean mix, lower compression, bad fuel, mechanical issue in the valve train. Faulty O2 sensors can cause them as can a bad fuel pump, however those normally cause a P0300 (random multiple misfire) and not a specific cylinder misfire like a P0303.