I have a 2003 2.0 ZX3 Zetec Focus. Starting a couple of weeks ago my car will sometimes self accelerate when I let of the gas. Sometimes when it shifts gears it will also jerk a lot. I have noticed the temp stays low for a while much longer than it used to. All of the problems seem to amplify when I run the AC so I have not been running it. I got two codes yesterday P1289: Unknown and P0128 Coolant Thermostat. Some background replacements are I had my Thermostat replaced roughly 6 months ago because it was leaking and about a month ago I replaced the Head Temperature Sensor hoping that would help my stall out at start issue I've had for years. Anyone have some tips for checking health of thermostat and what else might cause these codes?