In Reply to: 535 Running Rough and Rich posted by Jeff on September 26, 2001 at 11:22:02:
My '89 535 is difficult to start at first. Then when it starts it runs rough and I can smell gas. Then the idle will even out. But then after idling fine for about 2 minutes it starts to run rough again and I there is a "rich" smell coming from the exhaust and you can see that the tailpipes are blackend. Here is what I have done so far to try and fix the problem:
1. Installed the inline "check valve" at the fuel pump.
2. New oxygen sensor
3. New exhaust
4. New Plug wires, Cap and rotor.
5. New Coolant temp switch
6. New Spark Plugs
7. Six new Injectors and O-Rings.
8. Cleaned Idle Control valve.
9 Check computer and no fault codes are stored.
Could it possibly be the fuel pump, idle control valve or fuel pressure regulator? The pump does make a loud buzzing noise, but I cannot see how that could make things run rich. Any help anyone can give me would be much appreciated! Thanks!
Jeff, i'm no expert with the big 6, but the symptoms you describe are similar to what i had when my throttle position switch (tps) was sticking. I'm not sure the 3.5L has the same set-up, but it's worth checking. On my car this switch sits in a bad spot under the throttle body/intake manifold and gets gummed up pretty easily. Don't bother trying to clean it, just get a new one. The 2nd place to look (since it sounds like you've tried everything else) is the air flow meter, which will give you similar problems when it begins to die. I replaced mine at around 120K. Mine started out as a hot start problem, gradually got worse, the idle speed creeped lower ~400-500 rpms, and eventually got so bad, the car couldn't hold idle and would quit. New AFM, no problems. Have you noticed a lower idle speed? it should be 700-750rpms. Good luck and don't forget Rule #1 of backyard diagnostics...always start replacing the cheaper parts first.
ron 89 525i