On my 1988 626 I had the TB replaced once, The new belt was installed - one
tooth off timing . Idle speed went unnoticeable, but on the road, there was
no power ! Would take twice as much time to accel than before. Was very
noticeable , specially on a 110 Hp 4 banger.
I suppose some valves were just a bit open when they should have been
closed, and the other way around. No need to say after 2 blocks I u-turned
back to the garage!