Its hard to guess without experiencing the problem first hand, driving the car and performing at least some diagnostic tests. I would suspect there is a vacuum leak air intake boot? Is the idle speed very low?
I had the same problem with my 92' 9000 turbo the cause is usually the TSA system even if the light doesn't turn on the electronic throttle is idling too low to keep the engine running. Try switching the one way valves on the firewall and near the battery with each other to see if it repairs the issue otherwise it may be a computer problem