My wife was driving our 1996 850R, with 150k, the other day when it started running very rough so we had it towed home. On investigation yesterday the car would start idle fine for a minute or two and then spit and sputter til dead unless I gave it gas which would cause lots of black smoke(very rich).Checked all vacuum line. and connections finding none at fault even the one running under the intake manifold which I replaced last summer. I have observed something lately I never noticed before, constant idle speed motor humms for about a minute after I shut the car off. I never noticed this with any of my 700 or 200 series cars. I removed the idle speed motor and it actuates fine when twisted quickly. Pulled three plugs and they are black from running full rich. I like fixing my own cars, can't afford the dealer, so I went and bought a 70.00 dollar Actron scanner. It gave me three codes two of which there is no iformation for. Code PO103(MAF or VAF A circuit high input) Code P1505(no information and Code P1507(no information) I looked at some information and found a code PO505(Idle control system malfuntion and code PO507 Idle rpm higher than expected. These code could be from some of the playing I did yesterday when I disconected the Idle Air Control vavle when the car was running. I cleared the codes with the scanner and started the car it still runs the same but the codes did not come back. I would greatly appriciate any ideas.
Thanks,Tom
Owner 91 780, 89 740T, 62 P1800, 79 242GT(soon to be turbo) and lastly my 850R(frustrated front wheel driver)

If all the plugs are black you might have a stuck fuel pressure regulator. The codes could be secondary to that.

Because you didn't get any codes regarding the O2 sensors, I would suspect the MAF. Clean the electrical connections and examine the wires closely for brakes. You obviously are not getting enough air, so check for restrictions and the pollution control valve down at the bottom of the turbo line where a vacuum line joines it.

Klaus
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98 V70Rawd(101Kmi), 95 854T(85K mi), 75 164E(173K mi)

Thanks for the help, It did turn out to be the MAF. Cars running great once again.

A good possibility is your front (pre cat) O2 sensor is failing or has failed. Just went thru this exact thing with our 96 850. Car had no power, would hardly idle, blowing black smoke, acrid smell to exhaust etc. The sensor itself has a fault code but it doesn't usually set
a code until it is almost dead. You can check them if you have a digital VOM. If it's bad, it's an easy DIY job to replace (see bay 13) On the sensor, (1) Use only Bosch sensors and double check that you have the correct one. Some
vendors has a chart that lists the wrong sensor for some 850's. (2) Treat it like glass. It has a ceramic tip inside the "nose". Drop it and it's probably history. (3) don't get
any of the anti seize paste from the threads on the sensor nose. Another possibility for your problem is a major vacuum leak. Bay 13 will list where to look,