My 2001 Toyota Avalon is losing gas mileage, what could be causing this?

This could be a number of things....Really need more info...Because if it shuts off when you apply the brake and let off gas at the same time it could be an inoperative brake power booster or loss of vacuum..( vacuum leak )..Try this but don't touch brake.....If it dies without touching brake It could be too many things just to try and guess which is the inoperable component..To save time,money and headaches you need to hook it to a scanner...Has it been tuned up..?.What is engine size..,what is mileage..?.Did it happen all of a sudden..Does it get worse or go away at times...and so on..More info is needed for me to just guess...It may be a Throttle Position Sensor..O2 sensor....etc...too many to list...Save a Headache and have it scanned...Auto zone and some parts stores will scan it for free just for your business.....Although in some cases ONLY a DEALER SCANNER will be needed to find exact fault....GOOD LUCK....

you may have a converter that is plugging up and needs replacing.if you get a back pressure test on the exhaust system this will tell if its the problem.

good idea, it may not give you a problem but it is time according to mileage, and good insurance for your trip

jkjjg

CHANGE THE FUEL FILTER, AIR FILTER

the most recommended is:

change timing belt
change autom. transm. fluid and strainer
check drive belts , if necesary replace
check brake pads
change brake fluid
check wheels align
check air and gas filter

Sounds like you idle air control valve is going bad. They start acting up on a hot engine due to sticking or high resistance through its internal windings. It will get to the point where the engine will stall every time you take your foot off the gas.
I suggest getting it replaced and the throttle body cleaned at the same time since it will need to be removed to replace the IAC.

she really shouldnt worry about it hate to say , but do have a question i know its a avalon and all but do you have a trailer hitch with harness on the car wouldnt ask if i havent seen it before i work at toyota dealer as a mechanic and when they wire the harness for the hitch they tap into the light circuit causes the flickering hope this helps

Your Avalon uses 5-30 oil, 6qt with filter. Trans is Toyota's WS(world standard) ATF(there is no dipstick) There are no grease fittings on the car.
All the maintenance schedules are listed in the owners manual per mileage.