I bought a 1990 Dakota 3.9 V6 this summer, rebuilt the engine and everything worked great. Now that winter has arrived, I get an erratic idle with cold starts. The idle goes up and down by at least 500rpms. After ten minutes of warming up the idle stays consistent. I replaced the idle speed motor and this did not fix the problem. There must be a temperature sensor somewhere that is causing the problem. Any ideas?

 

First just trying cleaning out the IAC. They become gummed up it can cause idle problems.

Its on the back of your throttle body, unplug the wire harness, unscrew the two torx 25 screws and pull it out making sure not to lose the oring. use some carb cleaner on the IAC itself and the port on the throttle body. wipe the IAC VERY GENTLY.