I acquired a 2007 Mini Cooper hatchback and 6 speed after my nephew forgot to reinstall the coolant tank cap, and the engine lost its coolant and subsequently overheated. Coolant was added and it was determined that coolant was leaking into cylinders 2 and 3. The vehicle has 69K miles, and within 1000 miles of the overheating incident, had a water pump replaced, and also a timing chain. The vehicle has sat for 10 months.

I removed the cylinder head (N12 engine) and sent the head out for resurfacing. Seven-thousandths of an inch were removed. The intake valves and ports were cleaned while the head was off (there was some minor accumulation of carbon). I reinstalled the head with the thicker head gasket (Fel-Pro 26453PT, 1.20mm thick) and new head bolts. Also, new Bosch spark plugs (ZQR8SI302) were installed.

I started the engine, but the engine had random misfires and wouldn't idle. Seemed to run well above 2500 rpm. I ran the engine for about 6 hours total to use up the gas in the tank. I added 5 gallons of fresh gasoline (pure gas - no ethanol) and also 5 ounces of Techron fuel system cleaner. I replaced the ignition coils - no more misfire codes, but the car still won't idle and the rpms seem to hunt below 1500.

Trying to operate the engine below 1500 rpm requires throttle. Got diagnostic trouble codes P115C and P2178. Short term fuel trim was -25. Seemed like a vacuum leak so I sprayed the intake and injector rail areas with carb cleaner while the engine was running, but there was no change in performance. I pulled the intake manifold back off and checked for cracks - nothing. I checked the EVAP purge valve (was closed and would hold a vacuum). Also checked the PCV line from the valve cover to the throttle body and the hose from the MAF to the throttle body - both in good shape - no cracks observed. Reinstalled intake manifold but left PCV line to valve cover disconnected and plugged. Started engine - same scenario: runs well above 2000 or so but hunts below 1500 and will stall if gas pedal is not depressed.

I removed the valve cover to examine cam timing. With crank locked in place both cams are in proper position (cam hold down tools install without trouble and both cam timing flats are horizontal and parallel). Reinstalled valve cover and PCV line, pulled spark plugs, and did compression test: 172-180 psi each cylinder. Reinstalled spark plugs.

I just installed a new MAF - engine still requires throttle to keep from stalling, but can hold engine speed to about 1000 rpm, although there is still hunting when I slow engine down to about 800-900. Short term fuel trim is now near zero.

Since engine can now be operated near 1000 rpm it seems to load up at low engine speeds. When I open the throttle there is some hesitation and engine seems to run flat (almost like a misfire) until about 2200 rpm, where it seems to clear up.

I'm looking for some guidance. I realize the write-up is long but figured more information is better than not enough. Am wondering about injector spray pattern. According to the previous owner (my brother-in-law) the car ran like a top prior to the overheating incident.

What do you think?