Had the same problem. Long story short, this is the only thing that worked after almost replacing everything including the ECU.
Reset you idle.
Idle Speed / CO Content
1) Pull crankcase breather hose off pressure regulating valve and turn it so
fresh air will be drawn in.
2) Let engine run at idle.
3) After approximately one minute disconnect the blue connector at the
coolant temperature sender.
4) Raise the engine speed four times to over 3000 RPMs and then let the
to idle (This cancels the hot start idle increase function).
5) Adjust idle screw if necessary.
6) Remove tamper resistant plug over the CO screw, rotate both adjustment
--- the idle speed is 800 30 RPMs
--- and the CO is around 1.2 %
7) Reconnect the blue temperature sensor harness plug.
Cool Raise the engine four more times to over 3000 RPMs and then let the engine
return to idle.
9) Check to make sure that the CO did not go out of specs.
--- If the CO is out of specs, check the oxygen sensor system.
10) With the settings correct shut off the engine and reconnect the crankcase