Speedo Problem

[Payback45]

I recently moved from Maryland to New Mexico. While on the trip I noticed that my speedo was inaccurate. The way I could tell was I would set my cruise at 70 and try to catch up to my wife who had set hers at a lower speed. Couldn't do it. Another way was my Garmin GPS. It would say I am going slower that my speedo said. I am wondering if the Throttle Position Sensor has something to do with that. I had also installed a TB Spacer before the trip and I was messing around with it.
To be honest I am not sure how long it has been like this.
the only mods to the engin are light weight crank pulley, CAI, TB bypass.

[jey]

How much is the speedo off by? What wheels/tires are you running? What's your tire pressure?

Many manufacturers make their speedometers slightly optimistic to account for people who upgrade wheels and increase their OD - better to be too high than too low.

It has absolutely nothing to do with your TPS.

[Payback45]

It is off by about 3-4 Mph. It will say I am at 70 but I am really at 66-67. I have stock rims and tires. I am running 32psi up front and 30 in the rear.

[Sarra]

If it's your BE, then double check that you're running 205 55R16 tires.

[Payback45]

Those are the tires I am running. I wonder if it is something I have done or has it been like this since before I got the car?

[jey]

A lot of cars have optimistic speedometers rolling right off the showroom floor - 4% is nothing to worry about. If it really bugs you you can go with a slightly bigger tire next time you replace them - like 225/55/16.

[Payback45]

gotcha. It isn't a major concern but it was worth asking about.