I have a 98 gmc k 2500 with a 7.4l i have had a problem with a rough idle i have replaced everything i thought it could be from cap and rotor spark plugs and wires to fuel pump to fuel pressure regulator and fuel injectors and many sensors. it also has a problem starting and i dont know if this may be connected to this. also i have two code that pull up that i shouldnt have on my vehicle one is p 0034 witch is a turbo bypass vaulve code and the other is p 0072 witch is and ambient tempature sensore code and i have neither one of these features on my vehicle.

you should have a temp sensor, on my 350 its by the maf. ive read this can cause running issues because the pcm uses this value to change fueling to the incoming air temp

If you are getting a check engine light for a sensor, then more than likely, you do have that sensor. Its probably somewhere between the throttle body and the filter housing.

Rockauto.com shows a listing for a air intake temp sensor for your K2500. $16.94 for the AC Delco part.

if its the ambient temperature sensor not the air intake the ambient is what senses the outside temp would and I can not find it on my truck every where ive read is in the grille and I cant seem to find it

I have seen the ambient sensor cause the light to come due to the hvac using it. The vehicle i saw that on was a dodge minivan. Could be the same on this. The other code could be for something else sometimes the none manufacture scan tools will not give you the real code description. You could take the code numbers to the dealer and see if they can tell u what there are in there system.