Intermittent Loss Of Power, Misfire, Exhaust Leak Noise

[mynameis]

Greetings!

I'm a new member here on LOC. i purchased a 1999 RX-300 about 6 months ago. just completed the normal routine maintenance tasks, incl. RR all the spark plugs (NGK). the only problem i have is an intermittent loss of power (misfire symptom) accompanied with an "exhaust leak", air compressor sound/noise/rattle. this problem can appear with the engine hot during normal driving or cold at start-up. temporarily revving the engine will usually clear it up, return to normal operation. the "exhaust leak" sound is coming from the engine compartment area, but difficult isolate the specific source.

initially i thought the problem was related to a leak/failure in the exhaust system (incl. the CATs, cracked exhaust manifold) or a blown head gasket. with additional research the problem was looking more ignition related - one of the coils, but i'm not getting a check engine light so therefore no codes to pull. also, with the car in "P" there is a noticeable vibration/rattle when revving the engine. the vibration/rattle starts at the end of the power curve when the RPMs are decreasing, trailing off.

so with the great minds assembled here, what is the consensus about the probable cause of my problem?

i would just like to say i am very impressed with the overall design and performance of this car! fits all of our family' needs perfectly. well, it's a toyota. DUH! btw, i flushed the tranny with Valvoline MaxLife DEX/MERC ATF and noticed marked improvement in overall shifting performance. i had some flare in 1-2 and 2-3 shifts that is now practically gone. i noticed a lot of discussion on the web about which tranny fluid supplier to use and read positive remarks from RX-300 owners using MaxLife vs toyota, casrtol fluids. i would like to follow-up with a tranny additive. any recommendations? Lubegard?

thank you!

[Steve]

Hi, I just wanted to welcome you to the club, hopefully someone will be along soon to answer your question :)