On Jan 1 of this year, I bought a used 1993 Volvo 850 with 74,000 miles. It had never had its flame trap replaced. I had the flame trap replaced on Jan 25. Immediately after the replacement, the car began having a ticking noise and rough idling. I took it back on the same day to the mechanic who had replaced the flame trap, but he couldn't find the source of the ticking & rough idling. I took it to a different mechanic, who performed a compression test and discovered that cylinder # 2 wasn't getting enough compression. He said the most likely cause is bent or broken valves, and that a less likely cause is bent or loose rings. I asked why the ticking and idling problems would suddenly appear after a flame trap replacement and he replied, "maybe a coincidence." I'm not convinced it was a coincidence. Any thoughts as to possible relationships between the flame trap replacement and the ticking/idling problems?

Vacuum leak. Recheck the hoses going to your flame trap and be sure you didn't drop the large o-ring around the flame trp housing as it falls off easily.