Gas Pedal Stiffness / "Air Bypass Circuit"

Alright, here’s the deal. Just shy of 1 month ago, I had the engine replaced in my 1989 GT (spun rod bearing). The following week after the swap, I noticed my gas pedal started to develop stiffness. Although this never happened before, I merely thought it to be a throttle-linkage “dry-up.” So I popped the hood and CRC’d all moving parts involved in the throttle linkage, including the bottom pivot point of the throttle… door (what’s that thing called?). Anyway, it did nothing. The pedal still developed stiffness, seemingly more so immediately after I would floor it.

Then I realized something. It happened one day when I was pulling into my driveway. The pedal had been stiff for the previous 10min or so, but the moment I shut off the car, the stiffness went away. I had my foot just resting on the pedal ever so slightly, just merely touching it, the instant the engine shut off, and I could actually feel the tension vanish.

Backtracking… when my buddies were hooking the vacuum lines back up to the new engine, they lost track of where a couple of them went. This is what both them and I believe to be causing my “Check Engine” light to come on, for the code reader says that the “Air-bypass circuit” is at fault.

My engine is also burning rich, which is causing me to lose significant MPG.

Are the problems related? Could the pedal stiffness be somehow interlinked to the mixed-up vacuum lines? I’m almost certain the over-consumption of fuel is. Any input would be greatly appreciated guys.
 
First step is to unhook the throttle cable from the throttle body and see if the stiffness is in the cable or TB. You are saying that it comes and goes, my advice is to investigate it while it is present. Obviously that is when you will find the real culprit. Good luck, that is a strange sounding problem and I will think about it some more.