The truck is a 1989 Dakota, 3.9L, 5-speed, 4x4. I have a couple of drivability problems I am not sure if they are all connected.

When I start it up in the morning it will rev up a bit and the rpm will drop bellow idle and rev up again then settle out at its normal idle speed.

When I push the clutch in sometimes, to cost to a light or stop sign, the rpm will rev up a a couple 100 rpm and won't go back down to idle, 750 rpm, until the truck comes to a complete stop.

When I floor it, sometimes it will bog down for a second, then it will take off. I am not sure if that's just something you have to live with with TBI or if something is wrong.

Thanks,

 

My guess is a vacuum leak.

 

So I replaced all the vacuum lines inside the engine compartment. Also replaced the Idle Air control motor, the old one's gears were stripped.

I think I still got a leak though. I crawled under neath near the transfercase, there is a sucking sound. Is this sound normal with the transfercase, if not this is probably the source of my vacuum leak.

I also got a hold of a scanner, and I found out that she is idling rich. Could be a result of the vacuum leak or some other problem. Haven't drove it with the scanner yet, to see if its always rich or not.

 

The transfercase has a vacuum operated switch to control the CAD Central Axle Disconnect. The switch is on top of the transfercase. It probably is broken or disconnected.

 

So if its broke it would be inside the transfer case? Easiest way to test this, I guess would be to jack up all 4 wheels, put it into 4 wheel drive and see if the front wheels turn.