2006 b200, check engine light is on, car has rough idle

Look at tube from air cleaner filter back to the engine ,make sure there are no splits in the intake tube , air getting past the mass air sensor sends bad signals to the ecm.

I do not believe the two are closely related but try disconnecting the battery and reconnecting it again. Only the negative side. also check for a loos connection.

your idle valve may be dirty or needs replacing would check this as it controls idle. sits on the intake with wires coming out of it.

what are the codes

It can be issue with low fuel pressure,the fuel pump is getting old both needs to be checked.Also get the IAC valve checked.
Go through the related help links with similar problem,it may help:---
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Car still runs Rough after tune up?

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These details will help.
Thanks.

have the car checked for codes they will store them sounds like the cold idle sensor is staying engaged

In order to know what fault code is stored there, I suggest scanned the PCM to know it. Note this code number and send us for diagnostic additional and solution details .

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There are several reasons why the vehicle could be rough idling. If no check engine light is on and the vehicle feels like it's idling rough when you put it into gear. The transmission mount may be worn out which cause the vehicle to feel like it has a rough idle. Definitely at minimum you will feel the vibration when sitting in the vehicle.

Replace your spark plugs, and make sure all spark plug leads are fitted correctly.

I had the same exact problem on my 2004 Colorado (3.5L). Cleaned the MAF sensor (with MAF sensor cleaner) and throttle body/plate - cleared it right up.