My 2001 Cummins Ram intake manifold heater doesn't seem to respond in a timely manner when I plug it in anymore. Now it takes 15 to 30 seconds before wait to start light goes out. Does something need to be replaced? Can you plug it in too long?

 

The wait to start light has nothing to do with plugging it in. Plugging it in doesn't heat up the heater inside of your air intake ( which is why you are waiting to start ), plugging it in heats up the coolant in your engine. You SHOULD have heat relatively soon after starting it up as opposed to if you didn't plug it in at all.

 

I have heat after about 10 min.with high idle set and full heat after3-5 miles.I have it on a timer for 4 hours before drive time.