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2008 grand caravan P0300 & P0420

3.5K views 2 replies 3 participants last post by  chuzz  
#1 ·
Hello,

Van has rough idle on start up and rough running until engine has warmed up. Condition is worse after rain or in very humid conditions.

After engine has warmed, van runs ok except under conditions such as heavy acceleration, transitioning from downhill to flat or uphill driving or transitioning from cruising speeds on the highway to passing speeds.

What seems odd to me is if I downshift when running becomes rough it goes away. I.e. if running becomes rough when I attempt to accelerate to pass someone it feels like it is stuck trying to downshift from 6th to 5th or 5th to 4th. If i downshift manually the engine goes back to running smooth.

Not sure where to start with this one.

Any and all help is appreciated