Hesitation Mystery

Greetings all:

This past winter my car thru a U1000 code - lost connection with ecm when it went down to minus 30 celsius. Ever since then it has had a hesitation issue on small throttle applications. After replacing the Map sensor. Upstream O2 sensor. Coolant sensor. Plugs and wires. Even changed the throttle body and coil - I had spares. Not to mention the EGR valve and also had an Intake clean done. The final step was having the ecm/ecu reflashed with latest up date.

Well when it is in the garage and room temperature it seem to be cured for a bit. Once it has sat outside the hesitation returns. I though water from car may have got in somewhere. I can drive around it - it only happen once the efi has gone into closed loop/ fully warmed up and it feel like the throttle plate is deciding whether to open or not. With a bit more pressure on the accelerator and all is well. Usually happens between 2000 and 3000 rpms. It is basically a pain in the city - care is a 2007 aveo5 with 97000 kms on it. No codes have come up since the cold night back in December 2013 but the symptoms remain. Idles fine.

If you have any ideas - I am listening. I wonder if it is my big ass magnaflow sometimes causing fuel isses once the car has warmed up. Fifth gear is fine but one through four I can make it hesitate.

Thanks to all.

i would say a throttle body cleaning and a throttle position relearn procedure.

i can't say that 100%, but based on our description and attempts it sounds like something you missed.

Petrified Rabbit - thank you. Is this as simple as disconnecting the battery and turning on the ignition where the ecu does the throttle relearn or is there more to it.

Thanks.