missing and bad gas mileage

I just took my car to florida and back ( from Wisconsin) and got 21 mpg. I also notice that it is missing at lower speeds, it is probably missing at high speeds also but I just don't notice it. This is a 95 and is the same car I had problems with the alignment and a popping noise when turning. The dealer fixed the alignment but it is only good at low speeds, at speeds over 50 mph it starts to pull to the right. and pulls more as speed is increased. the popping noise turned out to be a subframe bolt. They tightened it up and the noise was gone for a while but is back now, I think I will find out which one it was and replace the bolt. Any suggestions on the missing and gas mileage would be helpful. The plugs and wires were changed at 75,000 miles and the car now has 115,000 miles.

Thanks

Dave Allen

The "100,000 miles until first scheduled tune-up" topic has been discussed in a few threads and has been collectively declared a BS Marketing Tool. A member posted that the Northstar ignition system fires on almost every piston stroke? or on intake, compression AND exhaust, something like that. This is a lot of zap compared to a traditional design and may be related to the factory eliminating the wires from the engine altogether on the late models. Anyway, soak up all the info in the "Valuable Northstar Engine Info" thread, but understand that even with AC Delco parts, the average plug and wire set life expectancy seems to be around 30k miles. Some have gotten much more, but most don't without experiencing problems again. You are at 40k on the set now. I'd say they have about had it, but pull a couple of the front plugs and see how they look. BTW, the engineers could never solve the carbon tracking problem that leads to misfire. The plug electrode could be fine, but look for black streaks running down the the porcelin from the tip where the wire snaps on.