1998 Dodge ram 2505.9 L V8 will hardly idle when cold once it warms up it's smooths out, is there a choke pull off or anything on this engine? Sounds like there's a vacuum leak when it's running really rough but it's fine once it smooths out
there is a couple of things is you could have a sticking IAC Motor (Idle air control motor) and its not letting it open enough ...or you have a bad coolant temp sensor and it thinks that the engine is not cold and not going into the correct fuel loop for a cold engine ...I would take the throttle body off and remove the IAC motor and clean them then after you reinstall them do a battery disconnect for 15 seconds ...the engine may not want to run at first because you reset all the values but just keep it running and once warm restart it several times
Also upon moderate acceleration the heater switches to defrost every time like there's a loss of vacuum soon as you let go of the accelerator pedal it goes back to the floor position
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