The 1994 850CSi is the ultimate E31 with a 375hp S70B56 V12 and a 6-speed manual, making it extraordinarily rare (225 built). Most common issues center on the aging ZF 5HP30 automatic in CSi siblings and shared E31 electrical/fuel/cooling complexity, though manual-equipped cars dodge transmission headaches.
Throttle Body Linkage and Idle Control Valve Failure
Common · medium severityTypical onset: 70,000-120,000 mi
Symptoms: erratic idle or stalling when warm, throttle body vacuum leaks, hunting idle around 500-1200 rpm, check engine light for idle control
Fix: S70 V12 uses twin throttle bodies with mechanical linkage that wears and binds; idle control valves gum up. Clean or replace both ICV units (2), inspect linkage bushings, synchronize throttle bodies. 4-6 hours labor including sync procedure.
Estimated cost: $800-1,500
Fuel Pump and Filter Clogging from Tank Corrosion
Common · high severityTypical onset: 80,000-140,000 mi
Symptoms: fuel starvation under hard acceleration or low fuel level, long crank or no-start hot, intermittent stumble above 4000 rpm, Check Engine Light for fuel trim
Fix: In-tank fuel pumps (two) fail from sediment; pre-pump filter clogs. Requires tank drop, pump replacement, new filter, sock screens. E31 tank access is labor-intensive. 6-8 hours labor.
Estimated cost: $1,200-2,200
Nikasil Cylinder Bore Wear (S70B56 Specific)
Occasional · high severityTypical onset: 100,000+ mi or sulfur fuel exposure
Symptoms: excessive oil consumption over 1 qt per 1000 mi, rough cold start that smooths when warm, loss of compression cylinders 1-4 or 7-10, blue smoke on deceleration
Fix: S70 used Nikasil bore coating vulnerable to high-sulfur fuel (pre-1996 USA). Requires engine-out, rebore to Alusil or sleeving all 12 cylinders, new pistons. 80-120 hours labor for full rebuild or replacement short block.
Estimated cost: $18,000-30,000
Rear Subframe and Differential Mount Cracking
Occasional · high severityTypical onset: 90,000-150,000 mi
Symptoms: clunking over bumps from rear, wheel hop under hard acceleration, differential alignment issues causing vibration, visible cracks in subframe around diff mounts
Fix: E31 subframe mounts fatigue; 850CSi 6-speed torque exacerbates. Requires subframe drop, reinforce or replace mounts, sometimes full subframe replacement. 10-14 hours labor.
Estimated cost: $2,500-4,500
Cooling System Hose and Sensor Failures
Common · medium severityTypical onset: 60,000-100,000 mi
Symptoms: coolant weeping from heater valve or auxiliary hoses, overheating at idle or in traffic, Check Engine Light for coolant temp sensor, expansion tank cracking
Fix: V12 has 20+ coolant hoses, aux water pump, heater valve prone to failure. Replace all hoses, expansion tank, thermostat, sensors preventively. 8-12 hours labor due to V12 access.
Estimated cost: $1,800-3,200
Instrument Cluster Pixel and Gauge Failures
Common · low severitySymptoms: missing pixels in LCD info display, erratic fuel or temp gauge, intermittent speedometer or tach, complete cluster blackout
Fix: E31 uses early LCD with failing solder joints and capacitors. Requires cluster removal, send out for repair (pixel fix, capacitor replacement). 2-3 hours removal/reinstall plus 5-7 day turnaround.
Estimated cost: $600-1,200
Self-Leveling Rear Suspension (EDC) Compressor and Strut Leaks
Occasional · medium severityTypical onset: 80,000-130,000 mi
Symptoms: rear sagging overnight or after sitting, compressor runs constantly, EDC warning light, uneven rear ride height side-to-side
Fix: Electronic damping control struts leak nitrogen, compressor overworks and fails. Replace both rear struts (EDC units), compressor, accumulator, check lines. 6-8 hours labor.
Estimated cost: $2,800-4,500
Buy only if you're a collector accepting $5-10k annual upkeep and have a specialist who knows S70 V12s — this is a unicorn, not a driver.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.