Ford Contour 2000 P0174 Code: Idle Hesitation, Low Compression, and Engine Misfires

Dear forum members and experts, I recently purchased a 2000 Ford Contour with a 2.5L V6 engine (98,000 miles). The car runs fine at idle when parked or in neutral, but experiences noticeable hesitation and misfires as it accelerates from idle to around 1500–2000 RPM. At higher speeds above 2000 RPM, the engine runs smoothly. I live in Arizona, where high temperatures are common — turning on the AC causes a significant drop in power, and the engine sometimes stalls. A diagnostic scan reveals a P0174 code (Rich mixture detected in bank 2). The previous owner reportedly attempted repairs, including replacing the fuel pump with a used one and draining all gasoline from the tank. I found a small green plastic tube leaking air connected to an elbow. I sealed it completely with black tape, which provided slight improvement. There is another green plastic tube that appears disconnected at the same location. I took the vehicle to a mechanic who tested both the old and new fuel pumps: the old one delivered 70 psi, while the installed pump (tested under the MAF sensor) produced only 40 psi. He performed a compression test on three front spark plugs. Two of the left-side cylinders showed 180 psi, but the right-side cylinder registered just 90 psi and was wet with oil. When he reinstalled the two good spark plugs and used a rubber hose to seal the faulty cylinder, the engine stopped running when he covered the end with his finger. The mechanic concluded that there is likely a valve issue or a leaking gasket requiring major repair — which would be very costly. After extensive research, I suspect this may not solely be a fuel system problem. The car had been parked for nearly a year prior to purchase. As an exchange student with limited funds, I cannot afford a full engine rebuild. Could anyone recommend affordable troubleshooting steps or potential fixes before considering major repairs? Thank you in advance for your guidance and insights.