3.9 won't idle
 

2000 3.9 automatic. runs good, just will not idle. i suspect the tps but would like some input from you pros

could be a variety of things. Main things to check, are vacuum lines, the IAC (idle air control) and the TPS (throttle position sensor) If the IAC has a bunch of black crud on the end, spray it with carb and choke cleaner and gently wipe it off, this may take a few times of spraying and wiping to completely get it clean. The TPS is fairly cheap to replace, but there is no sence in throwing money at a problem. Has the truck had a recent tune up? Has the gas been sitting in the truck for a long time?

new plugs wires cap and rotor two months ago, where is the IAC

i run a tank of gas thru in one week or less

IAC is on the back side of the throttle body. If it was the TPS you would have problems starting the truck too. Also check the Manifold Absolute Pressure Sensor. When the MAP goes bad it can really affect the gas mileage. Also a bad O2 sensor can cause the IAC to not allow the truck to idle and a bad O2 can cause a serious drop in MPG. A bad O2 will not always throw a code either. If there is more than 85,000 miles on the truck you may need to replace both upstream O2's and the MAP sensor. It's a good idea to clean the IAC at least once every 20,000 miles. The Haynes book for your truck has a lot of good info on the location of the sensors and how to test them.

Jimmy

getting good gas mileage. thanks for the help