97 dodge ram 1500 5.9L 145k miles 4x2

for the last 3 years my truck starts to do the same thing and i have taken it to the dealer and they cant even figure it out for sure.
when i let of the gas and under ~35mph my trucks rpms will drop and come back up if not to the point of killing my engine. there are also no codes. this seems to only happen when it gets cold out.

ive replaced

the iac 3 times
the crank sensor
pvc valve
purge valve
tps
ignition coil
the temp sensor (4 years ago before the problem)
new altenator (replaced when old one died over summer)
charcoal canister

 

Have you cleaned out the IAC bore in the throttle body? What brand IAC?

 

the most recent iac is from the dealer. i took the throttle body off lastnight and cleaned it spotless and it didnt fix the problem.

 

Test the TPS, make sure voltages are within range. (especially when you just pull your foot off the gas.)

Check the wiring for the IAC. Make sure it isn't pinched/shorted somewhere. Clean the connections at both ends just for good measure.

 

does this happen when you simply let off the accelerator or when you let of the accelerator and apply brake? Sounds like a vac leak start checking hoses and/or maybe your brake booster check valve

 

the tps is new i replaced it the same time i replaced the iac. it will do this when i ssimply let off the gas even if i dont step on the brakes. im thinking its a fauly map sensor that hasnt fully failed or a cam sensor.

 

Are you disconnecting the negative battery cable before cleaning/unplugging or replacing the sensors?

 

generaly i dont; i know you are sapossed to, but the neg battery wire is hard to remove and will always through the battery disconect code for a week or two.

 

could this be a map sensor?

 

You need to reset the PCM, so it can learn the new parts. Otherwise, you will never eliminate the problem.