98 740i 97,000 miles

On occasion my 740i has been getting obd codes P0170 and P0173 (Fuel trim malfunction bank 1 and 2). last year I spent about $500 replacing sensor and fuel filter and the problem continued and when the air got warmer it stopped. This winter it started up again. Sometimes it is every two weeks, sometimes sooner. Other than the car running a little rough for the first couple of minutes, it runs fine. Today the system added obd codes P0300 and P0308 (cylinder misfire Random and cylinder 8). I am trying to determine if this is potentially a serious issue. Any ideas of the cause and if they are related.

Also, is there a repair manual for the E38 i can't seem to find anything past the E32.

You might find this interesting...

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Thanks I am going to order tonight.