Short burst of low power

[wolfsbergjettagli]

1990 jetta gli
9a 2.0 16v
cise-motronic

After my recent top half rebuild i have noticed a problem. i noticed when starting cold or after about an hour of cooling down, ill drive it for about 30 seconds and then 10 to 15 second of low almost no power. after that every thing returns to normal and appears to work fine. im in college so i dont have much to to diagnos

Looked for
timing
bad coolant temp sender
vacuums leaks

any ideas?

[WaterWheels]

i noticed when starting cold or after about an hour of cooling down, ill drive it for about 30 seconds and then 10 to 15 second of low almost no power. after that every thing returns to normal and appears to work fine.

Looked for
timing
bad coolant temp sender
vacuums leaks

Timing, whether engine timing or ignition timing is not going to be time or temperature driven as you explain things. A bad coolant temperature sender is just that, good or bad. That goes for any vacuum leaks, they don't seal up after a few seconds.

Now there is something that would take about 30 seconds to heat up enough to send a signal the ECU will except and if that signal were to then be bad the ECU would revert to a pre-programed MAP (might appear to run fine but not "normal"). That part would be the O2 sensor. Have you tested that item yet?

[wolfsbergjettagli]

i agree with the O2 sensor issue

i started to notice this problem about 3 weeks ago after the head rebuild. the PO broke the timing gear position tooth and installed it backwards. he timed it to the mark on the reverse side which is slightly off from TDC a cog or two. wondering if that could have covered up the problem?