My 93 turbo has had a lumpy idle so I checked the codes. Only one is the 2-1-4, which is crank position sensor,
"RPM sensor signal absent intermittently"
The car runs fairly strongly but mileage is down. Other tune parts are good, compression is good, plugs quite recent.
Is there anything else that could be relevant to know about this? I will put in another sensor shortly, just wanting to have any other info.

the only time i got a 214 is when a bolt got loose in the bellhousing and bent the reluctor on the flywheel. and i've replaced many sensors that never posted a code. my guess is the connectors between the sensor and ecm are iffy or there is a slight miss taking place, rocking the crankshaft, jiggling the signal from the sensor and the ecm just posts the code because that signal doesn't look right. could also be the flywheel is slightly loose. if you replace the sensor and the code doesn't return, that would be a first for me. good luck, chuck.

Well last night the car was running pretty good, and after 10 mi, I went into a store. When I restarted and backed up the car died. That never happened before. It restarted and I decided to drive around a little bit to see what happened. It quit while running twice and restarted, then quit altogether. Attempted restarting gave only an occasional sputter and a couple of times while cranking the motor stopped, as though it got a spark at the wrong time and tried to go bacwards. I checked and code 2-1-4 has returned.
I got two more tested good, used sensors and will try them in the am, but the friend I got them from said he has found a short in the sensor harness someplace that then kills the sensor.
I have had a vibration in this car since I got it that no one has been able to diagnose (hi Bruce :-) I'm still stuck with it too) and have wondered about an electric issue, and about the torque converter/reluctor.
Hmm.

put in one of the known good used sensors and the car started right up. It does not run so well in terms of shaking like before and even More vibrations, which are now audible. But it runs and is back at home. More research...

Hi Jerry,

I'd think missing the crank signal intermittently would result in an omitted spark or ill-timed spark, both surely MPG reducers by allowing fuel to proceed through unburned, but if that were the case I say the seat of your pants would tell you before the wallet at the pump.

I'd suggest replacing the sensor if the cable is obviously broken (as they get) but if not, reset the computer and verify the 214 returns. VADIS says these DTCs are self clearing (when the symptom departs) but 214 is meant to track a transient. Not sure how long it retains. If I got a new 214 I'd swap the sensor regardless of its appearance.
--
Art Benstein near Baltimore

You know that indestructible black box that is used on airplanes? Why don't they make the whole plane out of that stuff?!

I replaced the sensor with a supposed good used one. The old one had no noticeable issue, except for a little bit of white stuff on the outside of the cable down near the sensor/block.
Idle seems a slight bit different but still lumpy. Idle used to be 750 maybe, had gone up to 8-900 but with no needle twitches while the shaking was evident.
But it is still lumpy at idle, which is now 700 at most, and again no needle twitches.
Running is def stronger; when the car has run the best it ever did, 3000rpm was 73-73.5 mph. It had gone down to 70-71. Today it was a good 74, almost 75 at one point, same road as earlier. And it seems to run a bit smoother. No codes.

I have a 92 740T wagon with the same turbo setup. That car is quicker, more 'eager' to jump up and run, downshifts more quickly, generally better performance.
Hmmm; any thoughts?

Dear jerryc,

Hope you're well and that New Year has started smoothly. I'd simply replace the crank sensor and see if that improves overall performance.

Perhaps frequent, brief interruptions in fuel flow - when the crank sensor's signal is lost, the fuel pumps lose power - are the reason that mileage is down.

Hope this helps.

Yours faithfully,

Spook