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high vacuum surge

John Hoegberg

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I have a 2.1 L turbo 4 cyl in a.... citroen ...evrything runs great pulls like a train under boost but at high vacuum and minute throttle openings (going down hill) the car surges any ideas on this? i've made sure tps is set up, tried rich/lean settings, advance/retard timing, messedwith the overrun vac value and to no avail.

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To maintain stable running you need sable fuel and timing.  If there are large changes in the numbers between zones you can get a cycling effect where it is too rich in one zone so slows down and falls into another zone where it is too lean and speeds up etc...  Make sure your table numbers are reasonably close.  Also have a look at overrun fuel cut settings if your ECU has them...

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