Interior:
1. Check the power seats on both sides. It's common to have the seat cable get bunched up and/or disconnect. It's a DIY or about $200 per seat, mostly labor.
2. OBC Pixels bad or missing. Also a common problem. I still haven't addressed mine. I don't use the OBC that often and can make out what is displayed. With some effort some E31 owners have been successful having BMW pick up the cost of the part and only paid installation. Some paid 50% of the part and split it with BMW.
3. On a '91 E31 the leather BMW used was very hard. The black leather esp. will look cracked and old. For about $50 a seat you can get the leather sanded and re-sprayed (dyed). I have done this to my black leather seats on the '91 I own.
4. Ashtray and coin holder lids broken or missing. Also very common. The coin holder design on the early BMWs was not very good. Fix it and don't use it. I removed my broken ashtray cover and use it as a cup holder since these cars come with very weak cup holders in the lower glove box ... which leads me to:
5. On a '91 you will have an upper and lower glove box. These are sometimes also broken at the hinge. Sometimes they are also not aligned properly. No big deal. Usually the two pop-up cup holders in the bottom glove box lid are broken and long gone... you're not missing anything.
6. Steering wheel rubber flex joint: I just learned of this myself. The E31 has a rubber joint in the steering wheel that will crack over time and allow play in the steering wheel or break entirely with potentially catastrophic results!
7. Auto up/down power steering function not working. Possibly a fuse sensor or worst case, controller.
8. Check all your switches and interior lights. Sometimes previous owners do not install BMW bulbs and use whatever they can get at the local auto parts place. For whatever reason (copper connections, etc.) the E31 is persnickety about the bulbs being only BMW. The light may work, but you may get a warning on the OBC (that is missing pixels LOL). I fought this demon myself with the brake light bulb and turn signal bulb.
9. General condition of interior. Check the headliner; open the medical kit and see if the door works, etc. You may also notice the seatbelts are integrated into the seats. The will auto adjust up and down with the movement of the seat. They will not work properly if the power seats are broken (see #1). You may also notice that the seatbelts are squeaky. Also normal. They rotate on a plastic-covered hinge that will start to get a cloudy gray film on them. The newer E31's came with a chrome-covered hinge. (Also chrome interior door handles). If the interior is in rough shape, chances are the rest of the car has not been cared for either.
Exterior:
1. The 8 sits lower than your average BMW even in stock form and the nose is quite long. The front bumper is integrated into the nose of the car. There is a black plastic lip spoiler that is at the very bottom of the car but is oddly recessed pretty far back form the nose of the car. Unless you really know the car, it's easy to rip off that spoiler on a parking curb. A valet or other non-owner driving, etc. will not know about this little detail. I have witnessed this myself as a passenger. $150 for the part and 8 sheet screws later all was back to normal.
2. Paint condition. You will be able to see very easily a re-spray on these cars since the odd angles and blending of the rubber bits with the steel are almost seamless. You will also notice a black rubber bump strip the runs down both sides of the car and blends into another bit of black seal between the plastic front bumper. Check the black strip and rubber seals for over spray or missed areas from being taped before being re-sprayed. Also check the front and rear plastic bumpers. Since they are the color of the steel body, it's a VERY tough job to match. You may notice some "stress rings" around the front Roundel. Also very common.
3. General condition. Again, lots of dents, dings, scratches, missing bits means trouble mechanically.
Mechanicals:
1. Loose steering. Could be the flex joint, steering box, adjustment nut, tie rods, any steering related bushings. The vague, loose steering is a common complaint on these older cars. It will not be as tight as your E36 as this is a GT designed for high speeds, but it should not have a lot of free-play in the steering.
2. Control arms and bushings. Very common on this and any BMW. The bushings for the E31 wear pretty quickly due to the weight of the car. It's a big girl. Heavy cars are hard on wear items. Ask if the control arms have been replaced/updated. '
3. DK Motors. Luckily (touch wood) I have not ever had any issues with these on any of my E31s. Do a search for "DK Motors" and read away. They just go bad. It's a common problem.
4. Heater Core. Check the A/C and turn it up. If you feel heat at your feet and coming through the windshield vents (either the driver's side or passenger's side) then you have a bad heater core. My last E31 had this problem. I used vent tape on the bottom vent until I came up with enough $$ to have to problem addressed.
5. Engine and transmission mounts. If the car shakes on idle but the engine is running smooth, you need to inspect the motor mounts. They are surprisingly easy to replace on the 850i. If you feel slight clunk when the car shifts (auto transmission) like the one you are looking at) then you may need transmission mounts. Again, they get old and wear. Engine is heavy, transmission is heavy. Did I mention this is a heavy GT?
6. Shocks. Not sure if this car has EDC, but regardless, if it has the original shocks then they will need to be replaced. Mine were so bad I could lift the hood on hard acceleration.
7. Headlight adjusters. The plastic adjusters WILL break if they are not already broken. Turn on the lights and check the alignment. You may be able to get BMW to replace these on their dime as well. Otherwise a member on this board sells a metal replacement similar to the upgraded metal units that BMW now uses to replace the plastic units. Do a search for headlight adjusters to get more info.
Here's a little list of what I have repaired/replaced on my "bargain" '91 850i six speed that had 104K miles on the clock. I paid $14,500 for the car in June 2004. All prices include labor or shipping.
Batteries replaced BMW OEM with labor (two in the trunk) $487.00
4 Wheel Alignment $99.95
Seat Repair and Dye (all four seats) $175.00
Black leather armrest for AutoChic $159.00 (incl. shipping)
Bilstein Sport Shocks $639 (incl. shipping) + H&R Springs (this is a mod) $176.00 + $300 install (springs and shocks)
Tie rods + Arm $523.16
Oil change (synthetic + filter) $218.04
Belts, Inspection II Service, AC compressor and retrofit kit from R12 to 134, upper control arms, lower arm bushings, radio code for radio, interior molding missing was replaced (below driver's side dash), repair sunroof not working properly, replaced A/C belts and adjuster pulley, two passenger seat cables broken, driver's side seat trim missing, installed new pieces, coin tray repaired, replaced front brake pads and rotors, replaced distributor cap due to bad fault, replaced ignition wires and ignition rotor, repaired windshield washer fluid sensor, replaced two cables in driver's seat for up and down movement, repaired vacuum leak at bank 2 with gasket for throttle body,
$4,494.05
Eisenmann Race Performance Exhaust (Round tips) $1622.22 + $200 install and custom fabrication of X-Pipe (replaced center resonator)
Replaced leaky radiator expansion tank $225.00
Full detail inside and out (the black paint was a combination of clear coat and none clear coat which suggests it has been repainted in some areas.. maybe a wreck, nothing in the history of the car. Since the clear coat black paint is just on the hood area, I think the PO just had the hood repainted to eliminate the rock chips these cars are prone to get with such a large swoop hood and nose). $125.00
Inlet hose replaced in cooling system. Had a crack and leaked. Hose, clamps, labor, etc. $107.00
BMW factory Anthracite mats front and rear for E31. $199.35
Window tint all five windows. $250.00
I have added some bits like AC aluminum shifter, factory leather shift boot, AC aluminum ebrake handle, AC aluminum pedal covers, aluminum door look knobs, and currently having a brushed aluminum dash kit installed. The black interior is really dark IMHO.
There are probably other items that I missed. Other owners can chime in and add to this list.
Bottom line is this: This is a GT! It's not going to drive/perform like your lighter and nimbler E36. This car as an 840 V8 or 850 12 cylinder has similar power and torque. One thing the 850i owners don't have the option to do is install an affordable off-the-shelf induction kit to our cars. There are some homemade options, but they are expensive. Dinan made a kit that is not even close to being affordable. The 840i however can accept a supercharger or turbo easily making it a screamer. Look up 840i supercharger for more info. The V8 in the 840i was a common cross-platform engine, so more modifications are available engine-wise. There are not any US-spec 840i E31s with a manual transmission however.
If you want a smooth, quiet, fast (not quick), unique everyday drivable exotic GT then the 8 Series is a wonderful choice. Unfortunately, this car was ahead of its’ time. There are many more high-line $100K+ GT’s to choose from these days (Bentley Continental GT, Aston Vanquish, DB7, DB9, MB SLC). The public fell in love with the looks of the E31, but not it's moderate stock performance. The looks of the car attract many buyers like you to take the plunge. Especially when the cost of these cars on the used market have reached an attainable level. The ongoing issue I see with the E31 specifically is that the new owner will not have the resources or time to restore the car to it's proper mechanical and cosmetic condition and it goes back into the used car rotation with potentially more neglect.
One last "gee Dad give me more advice" tip: If you can just barely afford to buy the car you are looking at, pay the insurance (which is quite high on the E31 by the way) and gas then I would not suggest that you purchase the 850i you are looking at. At $11,500 there are demons lying deep in the car. Trust me, I've done this 3 times now. Minimum I have spent is $5000 per car just to bring it to STOCK condition.
Good luck and ask lots of questions of the seller.
Sean
