I've had ~20% drop in FE recently on my last two tanks. I'm currently blaming some gas from a strange station, since that purchase sort of coincided with the change. But I have doubts on about that being the cause...
The engine is idling great - so smooth I have to look at the tach to see if it's running. But I feel some hesitation/stumbling during acceleration and cruising. I don't have exact TPS numbers, but my foot-o-meter says it is taking more throttle to do everything. Everything else, like temps, trannie, tires are normal. And I've made no mods lately.
Can you guys think of anything else that could cause a sudden change like this?
Check vacuum hoses too.
They like to get cracks, especially near the ends where the connectors are.
Also check thermostat. If you know what your upper radiator hose normally feels like, grab it when it's idling fully warmed up and see how it is. My rule of thumb is, if you can grab and hold on and keep your hand there, the t'stat is letting it run too cold.
Oxy sensor can also go bad. Testing needs a voltmeter. If it's a simple 2 or 3 wire sensor you can look up the procedure on the web, just google for it.
Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.
For me it has been the heat. I had a great 40 mpg tank, then ka-pow: A/C use, extreme temps and a miserable 30 mpg tank. The latest is around 34 -- close to usual, but still not as good as what I was getting.
For me, routine maintenance is overdue: oil change, air filter, etc.
Additional maintenance pending: Leaky valve cover gasket, A/T fluid change.
Here's the biggest problem lately: the school traffic pattern. Leaving at the same time as I usually did, I now get stuck behind buses, additional traffic to high schools (and not the best of drivers either), and the highway is more clogged-up -- theory: parents dropping kids off at the same time and hitting the highway in a big clump.
If these don't apply, then the other suggestions so far are quite valid. Dragging brakes especially are a biggie.
Have you tried resetting the ECU? How are IAT's lookin'?
I just posted a really bad 35mpg tank, and I though WTF? My coasting distances have been shorter. So I started checking, and one of my brakes was dragging. I loosened up the caliper, and I can feel the difference! I know it needs replacing, but this has to last for a few more days. Maybe then I can hit a 40mpg tank!
Thanks, everyone. Water and IA temps are running normal; low 200's and 110 when ambient temp is in the 90's. No clutch - automatic, which seems to be working normal. I replaced the O2 sensor this summer, and reset the ECU. Mileage improved after that, until recently.
I have the tune-up parts, but I've been sick for a couple of months and haven't had the energy to do many mod's. I also bought a new wheel bearing last weekend. I hope to get under the car this week. I'll let you know what I find. I will check the brakes when I have the car up on stands. I'll also check vacuum hoses. I haven't smelled it, but I'm gonna look at the gasoline lines while I'm under the hood too.