Welcome to the forum! Poor idling is usually a bad plug. There is no idle adjustment on the EFI models. The chatter is the rear brake. Sounds like the end of the world! LOL Main complaint on the Prowler for all years! There are numerous fixes to solve the issue. 1) Replace the Rotor, as it may be warped, 2) Replace the Anti-Rattle springs on the rear caliper, 3) Add a piece of rubber to the anti-rattle springs, 4) Convert to 4 wheel brakes, and 5) Learn to live with it! LOL The rear differential leaking out of the vent is a sign of either the bladder leaking, or the differential lube is over filled. Should be about 1/2"-1" below fill plug. There should be a bladder on the vent line. Keep your oil changed, keep the air filter clean, and enjoy! I use a good quality synthetic oil in mine, I change it every 300-600 miles depending on use (dust will kill these things pretty quick!), make sure any oil you use is wet clutch compatible. AC just released a 10/50 synthetic that many have switched too. The air filter should have a foam pre-filter (behind the passenger seat), and the main filter in the air box above the engine. The main filter is foam with a spray oil treatment. Be careful not to apply too much. I use the Arctic Cat Store for parts look up, and they have fairly decent diagrams for each category in the parts book. I have an 09 XTX, and it has been a great machine! Biggest cause of failure is neglect, and abuse!