ive got a 98 v6 3.9 dakota with 31x10.5x15 mud tire on it.ive been only getting around 11mpg and seems like it has a really delayed throttle respnse i was wondering if any of you had any explinations,i did a tune up and new o2 sensors,ive got a air hog intake on it as well,and tried the engine cleaner SEA FOAM. but nothing,also every once in awhile it will start up and the RPMS would slowy go down from 750 to 0 and shut off in about 3 seconds.but it only happens about 1 or twice a month.

 

clean your throttle body, replace or clean the IAC sensor... Idle Air Control... Replace or test your TPS sensor... Throttle Position Sensor. All of those can cause poor throttle response and or stalling on startup. Dont expect much with bigger tires either, they only hurt your acceleration.

 

sounds like your IAC

 

could be a bad iac, take off your throttle body, it has a reusable gasket, and look down into your intake manifold. if u have to get a little dentist mirror and check the seals in there, if u see oil around the lower pan seal then u need to replace that gasket, i had this same problem, i did a full tune up and oxygen sensors and flashed my computer (disconnect battery and hold key in the start position for 30 seconds) when you have your throttle body off, take off your iac and clean it w brake cleaner, works better than carb cleaner and wont eat away the rubber seals. also, did u make sure the plugs were all gapped properly? what plugs, wires, cap and rotor did u put in there? if u go to http://www.hughesengines.com/partDet...amp;eTypeID=10they have a great kit w wires and cap n rotor for a very cheap $90! then get the good ngk iridium plugs for this truck, i found these work best. and as far as the bigger tires go, youl see a little drop in gas mileage, not enough to make u go from a maybe say 18 (ive gotten 20) to an 11. the cold weather will also hurt the mileage, gas stations use more alcohol content in the gas which burns quickly and easily, and also keeps your tank from freezing. but anyway. double check everything and let us know whats goin on! -Justin