City gas mileage is awful -- I'm getting 12mpg if I'm lucky. I'm shifting around 2500 (unless I'm in a hurry), never really going past 3rd gear (downtown, stop-and-go), and running on 91 octane; AC has been deleted. I bought an o2 sensor but haven't gotten around to installing it and I'm not sure it's going to help. Car in question is my '90 CQ. Thoughts?