spi valve seat
My car didn't give me any warning,it just lost all power and wouldn't keep running unless I kept my foot on the gas.Then I looked on you tube and found a focus making the same noise as mine, thats when I realized mine had dropped the valve seat. I bought most of the parts on ebay all together it cost me about $500.00 to fix it myself.Yours sounds like it might be plugs, wires, or coil pack. Mine was running like yours and I kept changing the plugs and wires and it would only run better for a short time.Then I was changing the wires and had a trouble light close to the coil pack when I noticed several cracks running the length of the coil pack. I ordered a new coil pack from Advance Auto online to save 20% off the price then went to the store to pick it up. That solved the problem.