1991 964 Turbo stumbles when cold
 

Hi Guys

had this issue for sometime and its driving ! me nuts
from cold start the car will stumbles and really hesitate very badly when accelerating even gentle up to about 3k rpm then picks up fine its really really bad like neck breaking jerking ! once warms up its fine and goes like a dream - first 5 mins of driving very unpleasant !

right now if I unplug the 02 sensor the car runs fine under all conditons just a little rich ? but barely passes emission testing , with it plugged in passes no probs

I have replaced sensor but hasn't made any difference

anyone seem this before im a bit stumped :-(

cheers
Johnny

I should add the car does burble/backfire a lot with throttle off de-acceleration but not on throttle

Have you checked for vacuum leaks?

Curious that it runs fine without the O2 connected. That system shouldn't be online
until the engine has some temp-maybe a bad thermal switch?

Warm up regulator? Common issue on CIS cars.

I agree with Ras, WUR would be my first guess. Maybe post this question over in the 964T forum, lots of knowledgeable people over there.
PS: see you already did post it there.
:cheers: