When my dakota is in park the engine will speed up and slow down in between 500 and 1000 rpms. My dad seems to think that the distributor cap, which was replaced a few weeks ago needs to be adjusted, but not sure.

 

Hi Jacob,

What engine do you have? What year and transmission?

It's not likely to be the distributor cap. There are no adjustments to it. You also can't change the timing - don't even try! You'll mess up the fuel sync.

Likely, it's a dirty throttle body or a vacuum leak. There are passages in the throttle body that get loaded up with carbon, this is normal. Also the IAC, idle air control valve, can get dirty. Cleaning isn't hard but you have to remove the throttle body from the engine to do it right.

If you have a 3.9, 5.2, or 5.9 it may also be a plenum gasket problem. It's also common.

Post back with the info and we'll go from there.

 

It's a 2002 3.9L automatic

 

When's the last time the plugs, air filter, etc. were changed?

Try this, take the air hat off so you can look into the throttle body. Open the throttle all the way and with a flashlight look for oil. If you see any it's a plenum leak, very common.

If that's good, how comfortable are you removing the throttle body for cleaning?

 

I'm having a similar problem with an '04 4.7 automatic, I'm comfortable taking the throttle body off, but would you mind elaborating a bit on what I would be looking for to clean it?

 

http://www.oreillyauto.com/site/c/de...intake+cleaner This is what I use.

 

Awesome, thanks!