Unlikely that it is the modification that is causing that isue you are seeing, unless the modification screwed with the electricals. More likely, you have a problem with your idle-up circuit that is tied to the throttledobody. The idle-up circuit bumps up the idle speed when a heavy load is put on the engine, like the A/C compressor running.
Located on the back of the engine, between the intake manifold and the firewall. Looks like a box with an electrical connector and some rubber hoses running from it. It is powered by wire that runs on the passenger side of the engine, the rubber hoses run into the intake plenum and throttlebody.
If that circuit is working correctly, then I'd expand your diagnosic searching into something electrical or physically wrong with the compression (ie, drawing too much current, or the charging system is not able to keep up with a higher load (bad battery, bad alternator, loose belt, etc.))