Is it normal to get 22-23MPG in combined city/highway driving with A/C on most of the time from a '99 Mazda 626 ES V6 with a 5 speed manual transmission? The engine runs strong, idles extremely smooth (no miss at all). However, this mileage is disappointing for an engine so small in displacement. After all, the power this engine develops is nothing spectacular (170 Hp)

You probably won't get much better but an injector flush every 15k miles does wonders to get your best mileage. Techron works best because it decarbons the engine at the same time. It is possible to advance the timing a couple degrees above reccomended timing set and get better and more power. That depends on the fuel you run/weather conditions etc. If it clatters on accel with it advanced then drop the timing a degree until it does not clatter.

There must be something about Techron because I tried Chevron regular gas in this car several times and got gas mileage pretty much the same as when running on Mobil mid-grade. As you know Chevron gas contains some Tachron in it as an additive.

One thing that puzzles me is that Mazda recommends premium fuel in this vehicle and this car simply does not care fore premium fuel. It does not run any better on premium, nor does it get better fuel economy. Maybe if, as you suggested, I advanced the base timing a few degrees and ran the car on premium, I might get a little better peformance. I tried everything from regular to premium fuel in this car. Regular drops the mileage by about 1 MPG, but the car never pings so I would pretty much elimnate heavy carbon build-up possibility. The engine runs a little better after I replaced the spark plugs and plug wires at 64K. It seemed the eliminate the occasional hesitation at high speeds. I stayed with the original platinum plugs, which cost $ 7.30 a piece form sparkplugs.com (mazda dealer wanted $ 18 a piece for the same platinum plug). When you suggested flushing the injectors, did you mean just pouring Techron injector cleaner into the fuel tank or having the injectors cleaned by the dealer by running concentrated pressurized cleaner through the injector? They charge about $ 100 for running a can of cleaner through your engine. I pour a bottle of heavy duty injector cleaner through my gas tank about every 20K miles (this I get from the Mazda dealer). Is this stuff as good as Techron? I do not believe the dealer's claims that this car needs fuel system service every 15K miles. And what is this about cleaning the throttle body? I looked inside it several times and it was spotless.

I still have not replaced the timing belt on this car because doing so is a very tedious job and expensive if you have a dealer do it. One question: do you recommend replacing the camshaft sprocket and crank seals and the water pump/belt tensioner during the first belt change?
what about the valve adjustments? I would do it if I change the belt at let's say 90K. I may wait that long if I keep this car.

This car never runs perfect. something always happens that annoys me. righ now I am getting whining noise form the left front wheel. I just rotated the tires.

Nothing is as good as Techron that i have seen. Chevron does have it in their gas or so they say, but tiny amounts.I do reccomend replacing cam/crank seals and waterpump when replacing the t-belt. The tensioners usually go if the engine is overheated so i replace as needed.

i have a 2002 626 with the 2.5. auto. i get between 20 and 22 mpg. with under 20,000 miles

The gearing must be much lower on the Mazda because I also own a 98 Nissan Maxima with a 3.0 liter V6 and 5 speed manual transmission and it gets 27 MPG in combined driving with A/C on. And it delivers better performance than the Mazda V6.