low idle/stalling after harmonic balancer change ?

[turboLude]

Had a wobble on my old harmonic balancer so I swapped the old with the new,
and now have low idle while in Drive requiring throttle to prevent it from stalling

How can a harmonic balancer change cause this?
Could I have messed something up while doing this job?
What is my next step in resolving this issue?

[ga2001532]

Was it the same size?

[geoffinbc]

Did you disconnect the battery? What is the year/make/model?

[js35]

24x crank sensor I bet if its obd2