400 ISL Rough Idle

[Diplomat Don]

I don't trust my local repair shop so I thought I would throw this out here. On occasion, my ISL (2005 with 28000 miles) will idle rough after start up, both on hot and cold starts. I can't hear the rough idle, but I can feel it through the coach. It's really noticeable when I walk to the back and things are rattling, that shouldn't.

Often, a restart will solve the issue. I have no codes and the coach runs as well as ever. I track my mileage closely and there has been no change.

[GaryKD]

Hi Don,
Does this happen only in cold (lower than 50 degrees F) weather?

[Diplomat Don]

GaryKD....No, temp has not been a factor. It does it in cool and warm weather and will do it when the engine is hot or cold.

I'm thinking it's an injector, but it doesn't do it all the time and runs fine otherwise.

[Mike Canter]

I think the big question is why does it reset when you stop and restart the motor. If an injector was plugged or not functioning then I would think it would stay like that.

When it is running rough (especially when warm) is there any black smoke out the exhaust? Can you here a single miss when you listen at the exhaust? A put, put, put at a regular interval or is it just rough and sputtering?

When it is running rough after a start when warm what happens if you rev it up some? Does it smoke out the exhaust then? When running rough what happens if you hold the RPM steady at 1500? Is it smooth then? Does it go back to a rough idle when you release the accelerator?

[Diplomat Don]

It's weird.....no smoke and too loud with fan to hear any miss. No sound of a cylinder dropping out.

[Mike Canter]

Sorry, I wasn't clear enough. When I say to hear a miss I am talking about going outside to the exhaust and listening or holding a paper towel or rag right up to the exhaust pipe. Is there and even put, put, put or is a just totally an uneven exhaust with no repetitious beat. The difference is if it has an even putting sound out the exhaust pipe then it is one cylinder that is bad and then could be an injector. If it is an uneven roughness then it is something that is messing up all the cylinders like a sensor.

The other question is what happens after you start it and it is rough and you have someone bring the rpm up to 1500 while you are outside listening to the exhaust. Is it still rough or have an even miss or does it clear up? Does it stop being rough when you let it idle back down from 1500 rpm.

When is the last time you drained the fuel water separator?