The intake duct wouldn't have any bearing, the IAT, as long as it is functioning wouldn't cause issues either, even if you got it dirty. I don't think using brake cleaner on it would have affected it, either. The reading would have to be off quite a bit before the car starts changing the fuel tables.

I'm just going to assume that the cold weather is making the car run rich longer and the short trips didn't give it time to warm up as quickly so it burned more fuel. Plus a lot of gas stations are currently starting to get summer gas back in which does even worse in the cold weather than the winter gas with the extra ethanol does.

 

Another thing to consider is your transmission will not go into lock up until it reaches normal operating temps, and based on where you live and the short trip to the office, your converter is not locking up for the first four to five miles of that trip. My wifes 98 Trans am was the same way this time of year as her commute was also short and the car would use more fuel due to this.

The way to verify the converter is locking or not is to take your left foot and slightly ease the brake pedal down just a little while your right foot is on the accelerater. You will open the brake switch that cuts power to the lock up solenoid. You will feel the converter un lock and until you remove your foot from the brake, the you will feel the tranny go back into lock up (OD

When the tranny is not locking up in overdrive, you will burn more fuel because your cruising at a higher engine speed.

Just a little more food for thought. You have made all the checks that I know of. I think you may be burning more fuel because of the extreme cold temps up there and high idle time warming the car up before she drives it. The IAT senses air temp coming into the engine and has some bearing on timing and fuel curve and with that being said, colder air is denser and will require more fuel to be burned.

Todd

 

sheesh getting poor milage sucks i did alot of replacements and still gettin around 250 a tank on mines, best of luck to you though!

 

I really can't explain what has changed...
Fuel mileage is back to normal...
Thanks for all the advice!

 

Let's assume it was the cold weather and poor gas

 

Do you guys with the higher mileage put a higher grade of gas in or something?

 

I'm inclined to agree with Chibi.... Just a tank of bad gas. Hopefully NO more lol.

 

No. That would do more harm than good.

 

I run a can of seafoam once a season.