These what I've got from internet, hope it helps
check the obvious things... make sure everything inside the car works (buttons, windows, fan blower, AC etc..) If it has a sunroof, look for rust where the tracks are. Check the engine compartment for leaks, oil level & condition, straight frame, VIN # consistancy. Look in the trunk for water accumulation and the condition of the spare tire, also to see if the tool kit is complete and if there's any record of the last timing belt change. If all that checks out fine, take it to a mechanic to see if everything under the car checks out and get an abstract on it from the Ministry.
BEFORE YOU SHOP...
Before you decide to start looking at E30's, you must promise yourself that you will not be afraid to get your hands dirty. Even if you find a gem, there will be problems that you should tackle yourself. BMW's are no harder to work on then other cars, but repair shops love to overcharge you just because you have a German car. Make a commitment to buy a metric set of tools, a Bentley manual, and a few hours of your time to keep your E30 in tip top shape without breaking your wallet.
If you cannot change your oil, replace a fuse, or tighten a bolt do not buy an E30 because the little things will kill your love for your E30 and your bank account.
However, if you don't mind spending a few hours every once in a while working on you car, then owning an E30 will be a great (and cheap) experience.
WHAT TO LOOK FOR
The one thing I cannot stress enough is that low mileage E30's do not make the best buys for two reasons. First, the owners of low mileage E30's usually ask a premium (I will explain why it is a bad idea to pay a premium for low mileage E30's). Second, owning an E30 between the 100,000 mile and 150,000 mile interval can be extremely expensive. A lot goes on these cars in the 50,000 mile period. Why pay a premium for a car with 90,000 miles when you are 10,000 miles away from hell? It make much more since to grab a cheap e30 with 150,000 miles or more since the 100,000-150,000 mile problems SHOULD have been fixed. Please note SHOULD.
So what is so bad about the 100,000-150,000 black hole I keep referring to? Well between 100,000-150,000 the following parts usually need to be replaced or repaired:
Steering rack $ 500
Control arms $ 500
Driveshaft $ 800
Radiator $ 250
Brakes $ 500
SI Board $ 250
Timing belt $ 400
Battery $ 100
Clutch $ 800
Various electronics $ 0-1,000
Auto Transmission $ 1,000
As you can see, stuff adds up very quickly.
There are no guarantees that the previous owner took care of the 100,000-150,000 mile maintenance, or did the jobs properly. There is even the possibility that the car you are buying managed to crawl through the 100,000-150,000 interval with no problems. This could mean that you are gonna get hit hard with repairs in as little as a week!
Luckily there is an easy way to see what you are getting into. GET THE SERVICE RECORDS! I strongly advise buying an E30 without the service records. If the owner did not take the time to document the work done to the car chances are he wouldn't take the time to make sure the work was done properly. There is also the possibility the owner had the car serviced at an auto repair "chain," or "mom and pop" mechanic.
One of the worst things an E30 owner can do is to have their car serviced at a generic auto repair shop. BMW are special cars that need special attention from certified BMW shops or highly recommended local shops that specialize in high end cars. Using an automotive repair "chain" or a "mom and pop" mechanic can be murder on BMW's.
KICKING THE FENDERS
Here is a list of things to check for when you buy an E30.
Check all body panels for damage or signs of repair. Look to see if all the VIN numbers match. Look for anything out of the ordinary. Aftermarket spoilers or bodykits can sometimes be used to hide dents or damage. Check the head and taillights for cracks or pits. Make sure that all the door locks work properly. Check all trim and moldings for signs of overspray from a possible paint job. The hood washers, bumper trim, side moldings, door locks, door handles, and wipers should all be a flat black. If these are painted the body color the car could have a cheap paint job. Ask the owner if it OK to place a piece of making tape on an inconspicuous spot. If the car has the OEM or quality aftermarket paint job the tape should come of with no drama. If the tape takes tape with it, the car has been to a cheap repair shop. Look at the tread life on the tires. Also inspect the rims for damage. I also suggest that you get down and look at the under side of the car. Check for rust on the floorpans, drivetrain, and exhaust.
Look closely at the seats. If the owner has seat covers ask to remove them. Reupholstering jobs run $ 500- $ 2,000 for the front seats alone, so make sure the interior is in satisfactory shape. Check the dashboard and console for cracks or signs of wear. The carpet should be in decent shape. Ask to pull back a section to inspect the floorpans for rust (The carpet easily pulls back in the rear of the cabin. Make sure all buttons work. See that all the lights on the instrument cluster light up when the key is turned to position 1 or 2, and go dark once the car is started. It is very common for people to disconnect or remove the light bulbs to hid problems. Be sure the radio, power mirrors, power locks, power sunroof, flashers, turn signals, brake lights, fog lights, headlights, interior lights and AC work.
Engine bay and Trunk
Inspect the engine compartment and the trunk for signs of repair (The carpet will need to be pulled back in the trunk). The VINS should be found on both front fenders. The rear fenders do not have VIN stickers. Inspect all shock towers for excessive weld lines as it could be a sign of repair due to an accident or collapsed shock tower. The engine should be relatively clean. Make sure there are no leaks coming from the headgasket. Inspect the dipstick for signs of coolant (this could mean a cracked block). Check the condition and color of all fluid containers.
Check for a rough idle, hesitation, and knocks. The engine should be pretty smooth unless it is modified by performance upgrades like camshafts. Make sure the car can pull to redline without drama. Make sure the shifting is smooth and swift (short shifters can feel notchy). Check for a hard brake pedal and smooth stops. The handling and ride should be up to usual BMW standards (stiff but sweet). Make sure the E-brake is tight and holds the car in place. Don't be afraid to drive it hard! BMW's are strong machines that can take tough love easily if well maintained.
I strongly advise that you take your car to an independent mechanic for a check up before you buy. However, using these tips can eliminate problem cars right away and save you the $ 100 or so for a professional inspection.
It's actually pretty simple...
1. Choose the model you are interested in and set your price range.
2. Search the local Classified and Autotrader for the model you are looking for in your price range.
3. Inspect the car and ask the hard questions.
4. Take the car to an independent mechanic for the final inspection.
5. If everything looks good, buy it!
Chain tensioner and profile gasket, those are the major things
What color is the oil? ... any metal flakes in it?
How does the car idle? ...
does the car stay straight when you slam on the brakes and let go of the steering wheel?
does the steering wheel turn when you go over potholes?
any grinding or knocking (not ticking) in the engine bay?.. how about when you rev high then release?
what happens when you slam on the gas then release?... any knocking sounds from the shock mounts?.. subframe?
ABS kick in when you slam on the brakes?
any play in the steering wheel? ...
automatic or manual?.. if manual how's the clutch?... how easily does the car shift from 1st to 2nd without depressing the clutch?.. if you push gently it should be able to slide right in without any grinding.