I have van (yes a ticco) that is hesitates quite severely - but otherwise runs ok. It was a sudden onset of this problem, which not clear cause (at least to me)

I noticed, that during the hesitation the timing is running at 4 to 6 bdtc.

When the timing jumps back to more normal 14 bdts, it runs fine, and then begin to lug when the timing jumps back to 4 -6 bdtc. The timing change seems to be causing the hesitation.

The jump downward occurs when I apply the throttle at rpms less the 2,500 rpm. esp when on a slight hill - but immediately jumps back to > than 12 bdtc when I let up on the gas. On the free way, with RPMs over 3,000 all the time, the timing seems ok.

What function/malfunction in an injection system, ticco or otherwise,  would cause the timing to jump downward?