1990 535i Fuel Injection replacement?

I have never replaced my fuel injectors and wondering how to tell if I need to do this? The car is running a bit rough at idle, but runs well.

Thanks

Scott

m30's are notorious for a rough idle. There are many factors besides injectors that affect it (not saying your injectors don't need attention). I would start with adjusting the valves and gapping or replacing the plugs. New cap & rotor. Inspect the vacuum hoses for cracks. Put a whole bottle of Techron concentrate in about a 1/2 tank or 10 gallons, and take it out and drive it like you stole it. Get it good & warm & keep the rev's up and pull a few long hills or do some hard accelerations for a good 1/2 hour or more and then see how it runs.

Also check for any oil leaks. If the gaskets are weaping chances are false air is getting drawn into the intake that the AFM can't report to the DME. If you haven't chipped it yet, Mark's EAT chip will give it a smoother idle & make it more fun to drive :D

If you still think the injectors are the culprit, replace them or send them out to be cleaned. Obviously the valve adjust/plugs/cap/rotor/Techron is cheaper and simpler, but the injector job isn't that hard:

http://www.nmia.com/~dgnrg/page_17.htm

If you search the archives, there should be numerous links for injector cleaning/calibration services, about $20-$25 ea.

Five-O is a good source for new injectors. There was a time when near-new Mustang injectors could be had for $40-$45 for a set on ebay but that price has trippled. I put Mustang 19 lb/hr Series II injectors in mine and noticed a very slight increase in performance and smoother idle. To do it again, I'd get the Series III injectors.

Thanks, I will try the Techron in the gas and drive it hard. There are no oil leaks as I watch this carefully. I've also checked the vacuum carefully, but you never know.

sc