Everything. It would have been quicker to say what has not been replaced. Here is a small sample:
1. Wiring faults galore! Tail lights usually only half working due to the fact that the wiring is only covered by the trunk carpet.
2. Alternator packed it in three times.
3. Headlight adjust (on European cars) died.
4. Rear defrost stopped working.
5. LED clock resets itself usually once a month.
6. Fuel gauge needle bounces when tank full.
7. Fuel pump died and makes lots of noise when running.
8. Highest wiper speed is much too slow.
9. Ignition system died and left me stranded (again).
10. Cooling fans stopped working (in summer of course).
1. Transmission bearings had to be replaced.
2. Wheel bearings constantly being replaced.
3. Power steering rack replaced.
4. Brake rotors had to be returned.
5. Starter motor replaced which required engine removal.
6. Rear oil seal on transmission replaced three times in three months.
7. Power windows stuck and the drive had to be replaced.
8. Gas struts to support engine hood and trunk lid replaced.
9. Aluminum air conditioner tube rubbed on chassis and leaked.
10. Defroster position not selectable due to vacuum system design.
11. The fuel injected engine is much more reliable than the "carbed" ones, but it should have a water filter with warning light.
12. Camshafts had to be replaced because Maserati put a .7mm restrictor in each head to ensure oil starvation problems.
1. Headliner sagged so much it rested on my head.
2. The curved layout of the instrument lights are exactly the same as the steering wheel thus ensuring maximum blocking potential.
3. Button illumination is so dim they can't be read at night.
4. Rubber weatherstripping around the doors and windows have shrunk in length.
1. Sharp corners are a haven for rust which abounds on this car. Keep a wax coating on everything!
2. To protect the car add extra plastic wheel arch spray shields. You will have to make them yourself, but well worth it. It prevents water and salt attacking the chassis.
That's just the highlights.
A very unreliable car. Don't make this your only car unless you have a bus pass. I was stranded in Germany when the alternator blew and had no auto club membership, now I do. Don't even think about driving in the snow, the differential can spin you around in a second and the traction is marginal at best.
The Si is my third Biturbo. The other two either blew an engine (water in oil), blew the turbos, or had simply so many problems I had to put it down. I call my garage "my bank" since I usually pay about $5,000 per year just to keep the car running.
After all this you will ask why do I have a Biturbo? Easy, the car is unusual and not everyone has it. This will be my last Maserati. If you want a much better car get a BMW.