My 1985 245 (260,000) wagon has been a real workhorse, but now something is robbing it's power & has dropped fuel economy to about 17 mpg from the usual 23-24. It starts, idles and runs fine but acts like a the muffler is plugged. The cat does not rattle & I pulled the pipe loose at the manifold....does not run substantially better(no more power, only louder). Fuel filter is new, fuel regulator vacuum line does not suck gas & I replaced the O2 sensor. Vacuum lines look good but I haven't pulled the accordian off. I have sealed it before w/RTV and I think it's ok. I had the timing belt off for it's 5th change and it lines up correctly. The rubber on the harmonic balancer is slipping but I can time it by extending a mark from the hub as the keyway lines up at tdc. Idle is smooth but acceleration is flat between 2k-3k rpm. This one has me stumped. How do I test the air mass meter? Is the resistance between pins spec'd? I replaced this about 3-4 yrs ago when it would intermittantly/momentarily shut down the gas. Any suggestions?