Actually, sounds more like the engine tried to stall while they were feeding the cleaner in. The code was probably a misfire as the engine tried to stall.

My car did the same as I was using Seafoam thru the PCV port. I actually had a code reader, and came up with some interesting info: before you shut the car off after a misfire, the code will read P1399 which is something about a bad glow plug (diesel, eh?) apparently after you turn the car back on once the code has been stored, it converts to the correct code (P whatever for whatever cylinder misfired).

Cleared it once, never back since.

-Chris