I have a 2006 df175 250 hrs. I had idle problems at 1st. It was idling rough and would kill sometimes when I put it in gear. I changed the plugs and both fuel filters. The next trip it ran great. The 2nd trip it started idling rough again and killing when placed into gear. I researched the problems and cleaned the idle control valve (IAC). While doing this I decided to check the compression. I checked the compression on all 4 cylinders and they were fine. I did not disconnect the fuel lines and when I started the engine it back fired 1 time. I then started it and it idled at 1800 rpms. I replaced the IAC valve . I started it and it went to 2000 rps then idled down to 1500 rps. I tried to adjust the idle air screw but it did not change the rpm. I figured I now have an air leak. I inspected the entire system and cannot find any signs of an air leak. I then check the oil level and and found I now have water in my oil. The motor still starts easy and runs fine except for the high idle. I think the engine back firing caused the air leak. I took it to the dealer and when he saw water in the oil he said I would need a complete engine overhaul and I am looking at 7500.00. He advised it would be better to buy a new engine. I feel I can do the overhaul myself but I am not sure if it is a blown head gasket, some other gasket, or a cracked power head or engine block. With the high idle and water in the oil does anyone have and idea of where I should start looking for the problem
