Hi-

Recently had my oil and air filter changed. also decided to use a fuel cleaner (Castrol, i believer) claiming to clean the fuel injectors and remove carbon deposits, improving power and fuel efficiency. I've use them before on occasion to no ill effect. However, shortly thereafter i have been experiencing significant power loss (no acceleration uphill, but engine isn't straining or making any odd noises), also car has been idling a little rough and does not turn over right away on cold or warm days. finally, i noticed a decreased fuel efficiency (i mainly drive highways, and am losing 40 miles per tank in my usual commute). i thought maybe bad gas could be the culprit but after a few more fill-ups it's still lacking the spunk. i've got about 125K miles on it. had service done at 115K (new plugs, transmission service, fuel filter, PCV valve, vacuum hoses, etc).

any suggestions on where to start trouble shooting? fuel injectors? air intake?

also, i seem to have lost one of my rubber retaining rings on the exhaust (mounts exhaust to underneath of car). i have a spare, but i'll be danged if i can get the sucker on. any tools you can suggest?

thanks much-