I had a strange issue with my 2003 Ion. Sometimes after it came to a complete stop, it would give a big hesitation when trying to accelerate. If it happened once, it would do this every time you came to a complete stop, but would otherwise drive fine (occasionally stalling).
The strange thing was that if you restarted it (sometimes multiple times), this issue would disappear and not show up again as long the vehicle wasn't shut off again (you could drive stop and go traffic until you ran out of gas without it occurring again).
After a long time and a lot of frustration, I changed the ICM and it took care of the problem. I did not think it would work because I couldn't understand why restarting it would sometimes fix it.
When researching the problem, I could not find any one with similar symptoms online, so this is me just giving back in case any one has this issue.