I decided to try a can of CRC Intake Valve Cleaner in my FXT a few years ago...decided to spray it in through the open airbox even though there was an inconvenient 90 degree turn in the airpath just past the MAF sensor. I thought I had snaked the spray tube on the can far enough past the sensor and things looked OK as I sprayed the cleaner in with the car running (I forget the exact sequence I had to use, but I followed the instructions on the can).
Let it soak for an hour or so before taking it out for a spirited drive...I have a long driveway that is a pretty steep climb up to the street and, right when I finally got to flat ground, the car hesitated badly. It seemed to get going again and then I heard a sound I can best compare to a handful of ball bearings being thrown hard into a coffee can, followed by a near stall. At this point, I was pretty convinced I had destroyed my engine.
The car did recover from this without stalling and behaved a lot better as I zipped up and down hills and revved the car a bunch, although something didn't seem quite right.
Took the car to work next day and noticed that it was hesitating from leaving a stop...when I left work to go to the gym, I noticed three separate hesitations before the car got going (luckily nobody was coming). Started to worry that my car was wrecked again but did some poking around online and found that a fouled MAF could explain these symptoms.
Bought some CRC MAF cleaner and sprayed it up good that night, and the car seemed to go back to normal. Getting the sensor out was a PITA as it sits at the extreme left of the engine compartment and is pointed to the left...had to dig up a tiny screwdriver that I ended up dropping just as I was tightening the second screw putting it back in. Luckily, the screwdriver ended up on top of some plastic sheathing around the wheel well and I recovered it easily.
The FXT has seemed OK since then, although I can still hear that horrible metallic clashing like something from a recurring nightmare. I have since bought a Subaru tool for applying their valve cleaners and that has worked really well. I wondered at the time if the cleaner had pooled up somewhere on the way into the engine and then poured in as a liquid while I was climbing my driveway...