Poor Fuel Mileage

1997 Pontiac Grand Am SE V6 3.1L

OK, a quick history of this car since I purchased it in July 2007. When I first purchased this car I noticed the check engine light on. I had my mechanic do a full tune up, (plugs, wires, filters, fluids etc.) The check engine light stayed on after that work, and the car got about 13mpg. My mechanic and I took the car to Advance Autoparts to get the computer scanned and got the following codes (MAF or VAF Circuit Low Input, O2 Sensor CKT No Activity Bank 1 Sensor 1, TCC Circuit Malfunction, and Shift Solenoid A and B Circuit Electrical). My mechanic suggested we replace the O2 sensor and clean the MAF sensor. After that work, and a few miles of highway driving the check engine light finally went out. Fuel mileage increased to about 21mpg. Now a few months ago my car stalled while trying to drive through a flooded parking lot. After waiting awhile for the car to dry, it started but the idle was very high and the shifting was erratic, check engine light was on also. My mechanic and I changed the engine and transmission fluids and replaced the Throttle Position Sensor. Now after that, the car seemed to run fine, no check engine, light good gas mileage, normal idle, until a few weeks ago when the check engine light came on for no apparent reason. The car would idle slightly high at times, nothing like when I got flooded which was really high. Right now the car seems to run fine. The check engine light hasn’t come on in awhile, the idle is normal. But I’m getting 13mpg or less. Advanced Autoparts scanned it for me and mentioned something about a Pedal Position Sensor. Could this be the Throttle Position Sensor acting up again? It hasn’t been long since that sensor was replaced, but that is the only code they are pulling.

Thanks everyone for any help on this topic. It’s now time for me to go full up tank again. What a pain in the $$$!

MAF or VAF Circuit Low Input, O2 Sensor CKT No Activity Bank 1 Sensor 1, TCC Circuit Malfunction, and Shift Solenoid A and B Circuit Electrical

You didnt mention what year, engine and what .... see what we can do.

Check the MAF wires sometimes they get stretched out and when wet can short out.
Also if the Intake Air Temprature IAT is not working it, or its circuits are damaged, could cause the transmission to shift poor/bad.

It might not hurt to change the other O2 sensor, and get a fuel system cleaning.

Was anything done about the "TCC Circuit Malfunction, and Shift Solenoid A and B Circuit" ?? (other then fluid-filter change)

If these components are not working this could cause your mileage to drop.
Might even damage the transmission. :yikes:

With the service light poping off and on, youd have to get it scanned with it on.
Most likly it was a misfire, typical and after a few drive cycles it shuts off when things are back to normal.

Sorry about not posting the car info. I was in a rush and forgot to put it's a 1997 Pontiac Grand Am SE with a V6 3.1L. As far as the TCC code, I forget what that code is for actually. I think I remember the Advance Auto guy telling me it's something to do with the transmission. But I only focused on MAF and O2 Sensors. How difficult is it to replace the Shift Solenoids and the TCC? I'm thinking about just taking it to Aamco near me. I don't really trust the last scan I got at Advance Auto.

The TCC is in the transmission, though it can be changed DIY without dropping the trans. Here is a link to ther repair.
How To Replace Your Torque Converter Clutch Solenoid (http://autorepair.about.com/cs/doityourself/l/aa011703b.htm)

Most auto part stores scanners are not that good and dont read all codes. SO having Aamco scan it might show a little more into that TCC.

Good Luck

hey thanks alot xeroinfinity. I really appreciate your help.