15 Mpg
 

Well.....
2 weekends ago I changed the O2 sensor in my 89 NA, so I decided to track mileage after my last fillup and see what my approximate MPG might be. Well, the title of the thread says it all. I drove 181 miles and consumed a shade over 12 gallons of 93 octane pump gas. Granted, my driving is almost exclusively stop and go cityish driving, but this still seems alarmingly lower than the mid 20's MPG that is seems my car should be getting. Some more details:
O2 sensor replaced 200 miles ago
Air filter (stock) replaced approx 2000 miles ago
Fuel filter (external one) replaced approximately 10,000 miles ago
Plugs cleaned/gapped/inspected 200 miles ago, good looking tan color
Distributor Rotor and Cap both replaced 10,000 miles ago
Plug wires replaced 2,000 miles ago

That's most of the pertinent info I can think of.... I did notice that after replacing the O2 sensor, my car seems to idle a bit rougher, and occasionally stumbes a bit. Always ran very smooth with the last O2 sensor.
Car idles steadily at around 970-1000RPM
Exhaust smells rich at startup on cold mornings, but not after engine is warm.
When starting car at really cold temps (below 15 degrees F) the car starts and idles, but needs a minute or two to warm up before it accelerates correctly, seems to start missing a cylinder around 2000 RPM if I increase throttle right after starting up.

So what should I be checking out/diagnosing/troubleshooting etc? I'm thinking I should start off with FPR and AFM.....any other ideas? Thanks guys!SmileWavy

You could put the old O2 sensor back in and see what mileage you get. Mileage is low. Is engine getting to its normal temperature range? If it does not get hot enough, mixture could be too rich.

The old O2 sensor was the original with 70k on it, so I'm pretty sure it was shot. I also pretty much destroyed it while removing it (had to use a torch to heat up the exhaust). Engine is reaching normal operating temp without a prob, the car is used almost exclusively for commuting to work, about 1/2 hour each way.