I bought a used ECM at a salvage yard for $50, put it in and that solved my idling and speedometer problem. It was not the Mem-Cal or Prom chip that was bad but the ECM itself. I know that because they sold me the wrong ECM for my car (perhaps it was from a van or a Euro or something) so it ran rough and the speedometer was working but not calibrated properly. I switched the chip from my old one to the new one and that did the trick.