I used Pennzoil or MotoMaster Fuel System Treatment, whatever that's on sale at Canadian Tires. They did work well on our cars.
The MotoMaster FST once fixed the rough running and sudden dead problem on my wife's 325i that a mechanics tried with replacing the O2 sensor and a full tune-up but with no avail.
Hope this help.
1992 300E 4matic
1993 325i (wife's)