drop in mileage, what to check?

[dulog]

Ok the last few tanks my mileage has dropped. Most of my driving is city and normally I get mid 20's now I'm getting low 20's and even had one tank right under 20. I've checked tire pressue. The last time I changed the oil was about 2000 miles ago and it was with mobile1 synthetic 0w20 (previous oil change was 3000 miles before that using the same). Any suggestions of what to check? I've never kept close track of gas mileage until getting this car last spring, so is a drop in mileage normal when temperatures drop during winter?

[simdrew]

Just guessing here, but with the higher air density, the comp might be feeding the engine more gas to match--providing better performance and worse gas mileage.

[RyanJayG]

cold start up = more fuel as well

[cbcbd]

When is the last time you changed/cleaned your air filter?

Made a huge difference for my mileage when I changed mine.

[dulog]

I haven't cleaned or changed the air filter. I'll check that. Thanks for the tip.