tachometer reads oddly and poor performance
 

this is my friend's car, so i am not as familiar with it as i am with the 944's. however, it seems to have a very similar bosch fuel injection setup, etc.

this is an '87 325is.

it is running poorly (seems to miss, has poor power, runs rough, idle surges), especially when warmed up. it had a recent tune-up, including fuel/air filters, new plugs, new fuel line, fuel injector cleaning/rebuild, etc. what i found is that the rubber intake boot is very old and cracked. i know this needs replacing. how badly does this problem affect these cars?

also, the tach is all over the place. i am thinking it is either broken or has a bad ground, as it will read zero then 2500, then 500, etc., no matter what the actual RPM's are. any tips?

TIA!!!

I had a 93 325is that did the exact same thing with bad intake hose. A new one fixed the problem. It was only about $20 at the dealer.

thanks!