Random idle. Vacuum electric switch?

[arrowstrap]

ok, i wasnt able to find this in the book cause i don't know what it's called:

there is a vacuum line going to a harness just to the right of the ac box attatched to the firewall. from what i can see the hose ends there and the vacuum is used to position an electronic switch or meter. just beside the hose barb is a wire harness with several wires from it.

with the hose connected, i get an idle that is strong, then poor and it swings back and forth randomly. if i disconnect the hose, idle is strong but i get no power. i am haveing no other vacuum issues that i am aware of and the hose seems to have a good suction.

what is this and what needs to be serviced/replaced?

 

[bushpilot]

i bet a digital photo or two would help...

 

[action4478]

Is it the map sensor?....

 

[Zookie400]

must be....its the only thing that makes sense. unplug that and all the boost goes out the hose. as far as the smooth idle with it unplugged..... the good/bad idle you describe sounds like mine when the defrost or ac is on, and the compressor is cycling on and off.

 

[arrowstrap]

It is the map sensor. i looked up the part image and it's the same. so is my map sensor failing? hope not @ $150- $200 bucks for a replacement!

my AC is turned off.

With the engine running i can plug the hose in and create an erratic idle. as soon as i unplug it, the idle is fine.

also, this is not an issue once the truck warms up... as in it runs just fine with the hose connected. ????

 

[arrowstrap]

so, i pulled a po236 code. boost pressure sensor. this issue occurs every time the truck starts regardless of the engine temp... however while pulling the codes i noticed that i left the chip programmed in PERF TOW mode. i reprogrammed it to PERFORMANCE and NOT not tow mode and the problem (so far...4 startups) has not happened since. anyone have any ideas on this? my programmer a superchips.