Hi!
I'm getting a 2-3-1 fault code on my 1994 850 Turbo (with manual transmission) and the car is rough while idling after cold start (the ABS lights stays on a bit longer when is this happening). Also sometimes it looses power when going uphill and when doing so it starts to twitch - this happens around 3.000 RPM. Usually after the loss of power the Check Engine light lights up. After clearing the codes and the CEL the car doesn't suffer from loss of power for a bit but then this problem reappear. Sometimes it twiches when I get foot off the gas. There's no smoke but the fuel economy worsened.
Spark plugs, ditributor, timing belt with pulleys, boost control valve and O2 sensor have been changed a few weeks ago. The car is always running on 95 Octane fuel. I also got 1-4-3 and
3-1-4 fault codes before but they didn't appear again after I cleared them.
The car's got 100.000 miles.
Do you have any idea what could it be? Only fuel pump or some vacuum came to my mind...
Thanks a lot in advance!

 

I think you are on track with looking into vacuum leaks. How does the brake pedal feel immediately after a cold start? If it needs a firm leg to stop for the first few hundred feet, you may have a brake booster / vacuum assist pump issue or a faulty check valve - which can cause an intake air leak.. Otherwise I suspect the loss of power to be a more general vacuum leak - check the vacuum tree under the throttle cable spool cover - are all the ends capped? Any broken or loose hoses? How do the lines going to the boost controller look? If the caps have fallen off, it could be an early sign of a clogged PCV system as well

 

On a turbo, your vacuum leaks become pressure leaks and that helps you troubleshoot. In fact on my car it's not that strange to hear one under boost. The bigger ones, like where the big rubber parts in your intake piping die of old age. So the point here obviously is lean under vacuum and tending toward correct at part throttle and rich under boost. On a 94 I think you should have been required to to copious replacements of this stuff before now.

If you're going lean under boost, then that might be more of an indication that the fuel pump can't keep up.

I will just add that specifically for the 3-1-4 code, the camshaft position sensor does go bad, that's pretty normal. they will flake out and then work again and you'll be able to intermittently fail and no-start for months. Any time it screws up it's really easy for the computer to set that code. if the crank is moving and that thing doesn't act right, it should set a code again.

Taken with the "bad signal" code for the knock sensor, it sounds like the root problem might really be some bad connections. You could try to stupidly unplug the ECM and plug it back in, knocking off some dirt. Microsoft tuneup, so to speak.