misfire no code
 

Hi All,
I have a 2008 F150 4x4, 4.6 with around 165,000 miles. I replaced coils, boots and plugs around 120,000 miles.
I am getting a misfire at 45 to 65 mph and it seems like it is getting worse but will not throw a code. I took my truck to the dealer yesterday and had them perform a diagnostic scan. Their scan showed an intermittent misfire but could not determine which cylinder. Their diagnosis was a leak in the intake, causing a coolant leak which was causing the misfire and they would need to replace the intake, gasket, plugs, boots, thermostat and other small stuff for $1300.
I have read through many of the misfire threads and never heard of this problem. I have dealt with coil problems before but would get a code which made for an easy diagnosis and repair. Without a code this is beyond my level of experience.
Any recommendations or suggestions would be greatly appreciated.

My 2003 F150 is running super rough.Plugs and coils about 4000 miles in.Total on truck 162,000. Engine is the Triton 8.Any help would be appreciated. Thank you!

I wanted to give quick update. After I left the dealer Tuesday I went home and took my air filter out and put in another one that I had, I have a couple of different cleanable filters, and also cleaned the M.A.S. and did a visual inspection on the top of the engine looking for any leaks. My truck still had the misfire when I drove to work yesterday morning and figured I would have to try to chase down the problem with a coil, boots or plugs this coming weekend. well when I drove home yesterday the truck drove perfectly, apparently cleaning the M.A.S. and giving the computer time to reset itself resolved the problem. When I got home I got up on the engine with a good flashlight checking once again for any visible leak, since that was the diagnosis that I got from the dealer, I cant find any sign of leakage. I wonder if the guy that did the diagnosis just did not want to bother with tracking down the problem and figured he would go for a big ticket fix.