[LocoJason]

Just figured I would share...

A few months ago, my TPS developed a dead band from about 25-50% throttle. This is fairly normal in higher miles cars and generally sets a P0122 code. As I use a scangauge I noticed almost immediately that when the TPS value fell off, my fuel economy jumped up substantially. I was very skeptical at first (as I'm sure you are), but verified after several tank-fills that the increase in economy was real.

The only conclusion I could come to was the ECM did not disregard TPS input despite setting the code. So there's a corresponding reduction in calculated load and most likely a notable fuel cut taking place because the ECM 'believes' the driver has let off the throttle. Ignition timing advance would also be reduced from ~25 to ~15 degrees BTDC when in the dead band :-( The end result while steady-state cruising the dead band, it gained 3-5 MPG according to the scangage and almost 3MPG overall per fillup.

So I decided to wire a small switch into the TPS so I could manually trigger the dead band at any point. Not surprisingly, at most higher speeds and loads there was a substantial reduction in power and a lazy feeling to throttle inputs. Still, my fuel economy was up and I didn't have to spend anything...

I do not have any instrumentation on the car such as an EGT thermocouple or a wideband O2 sensor, so I can't confirm the amount of fuel cut taking place or the increase in EGT. Running lean and with less ignition timing advance raises EGT substantially. Still having a working catalytic converter, I am mostly concerned with damaging it due to the high EGT's so I plan to install one. I've been driving this way for a month now and I have had no issues yet. I wonder how many other vehicles have logic that allows this to be a 'mod', essentially enabling a lean-mode for better fuel economy.