Wont Hold Rpm's

[89GMC27]

My 89 GMC was in a front end collision the right fender hood and radiator support were damaged. I have since replaced the entire front clip but even before doing this the truck will not run right. When started the truck wont idle it will stall out so i give it gas to keep the rpm's up and keep it from stalling, however when i do this the rm's will increase inicially but then die again even when the pedal is still depressed. If I let go of the pedal and depress it again the rpms will again inicially jump then die.

 

I was thinking that it might be a vacume line leak but im not sure and wanted to see if any of you had any other thoughts before I went hunting for the leak and possibly replace all the lines.

[lbkthree]

I had a similar problem with my grand prix and it was infact a vaccum line leak. Replaced the line and that was all. I found it by using the old starting fluid trick.