95 525i M50 Running Really BAD - (kinda long - sorry)

Hello All, I'd appreciate any suggestions. Don't know if it's related, or just coincidence, but here's how it happened. After the two recent storms hit the gulf coast, I found myself low on gas
one morning, only regular unleaded available no matter where I searched, being desparate and almost out of fuel, I had to settle for regular unleaded, and with no octane booster for sale at this outlet, I opted for a bottle of STP Fuel Additive and a few gallons of 87 Oct until I could find some 93. Later that day I found only 89 Octane, so I pumped about 10 gallons and added a bottle of Octane booster. Well, maybe coincidence, maybe not, but a couple of days later my car began running badly, idling rough, like a misfire, but not a steady miss, and when under load, it just sputters and misses really badly. I have to accelerate really slowly in traffic to avoid the really bad midfiring and sputtering, but even then it's still there. Thinking maybe I pickup up some trash from the fuel tanks at the local outlets since they were being filled, emptied, filled with the demand on fuel, I changed the FUEL FILTER to no avail. Then changed the SPARK PLUGS thinking the recent mix of additives, octane booster, low octane fuel may have fouled the plugs. This didn't help either. Eventually I will get a proper dealer diagnostic, but I haven't given up on fixing it myself yet. I'm not convinced I don't have a VACUUM LEAK somewhere but have tey to investigate it thoroughly yet. Maybe intake manifold gaskets, or any of the numerous vacuum hoses. So, do you have any other thoughts on what to check? I did a voltmeter check on the Throttle Position Sensor, and according to my Bentley, it didn't check out, but I'm not altogether sure I tested it correctly. When moving the throtttle plate slowly and expecting to see a change in the resistance across the specified terminals, the value didn't change at all, like I wasn't moving the throttle plate at all. Do any of you have knowledge about TPS to know that it is definitely bad, based on the results I just noted? What else on the M50 would cause this poor running? I appreciate any help!!
K Benoit South Louisiana
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I think that you would hear a vacuum leak, especially if it was bad enough to make the car run crappy.
My guess is that you have a bad coil. Having said that, you should have a Check Engine light if it was true. I do not think the gas itself is your problem. You _could_ have sucked up some crap from the gas that is causing problems, but using 87 or 89 octane gas shouldn't be your problem. If you had always pumped 91, AND got the same crap in the tank, then you would have the same problems. Get it? You could have gotten some bad gas, but the octane rating by itself isn't part of your problem.

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go to http://www.bimmer.info/forum/forumdisplay.php?f  post there, they will help you out. If it is a coil, there will be "candy" leaking out of it - easy to see if it's bad
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I *think* it's just a switch rather than pot. Can't look it up at the moment.

I'd say the best way would be to have the codes read. This should give the problem.
--
*Time flies like an arrow. Fruit flies like a banana.*

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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KJB wrote:

Huge snip of stuff
OK - your car would run just fine on 87 octane. It would make less power but it would still run fine. Your car has a knock sensor that will retard the timing when you run lower octane.
Putting 87 octane in has nothing to do with your problem.
More likely - crap in the tanks, as you correctly surmised. Thing is - even though you changed the fuel filter - if there was still some remaining crap in the tank, the new one could now be plugged up. The only sure way to know the crap is out of the tank - drain it (not a trivial exercise since you have to get rid of the fuel somehow.)
The other possibility - the injectors are plugged up with crap that managed to get past the filter. This is rather unlikely - since the filter is VERY good at filtering out anything that might plug the injectors.
How close were these stations to the flooding areas? Might water have gotten into their tanks? If so - some fuel dryer (alcohol based)would be a good thing.
The STP stuff is basically a waste of time. If you want to add elixirs to your tank in the hope that a magic formula will make thing better - the one BMW used to sell (repackaged) and the one that is known to do some good is Chevron "Techron" - available at your local auto parts store.
Vacuum leak? Sure - anything is possible - coincidences DO happen - but a leak that would cause it to sputter under acceleration is a BIG leak and as someone pointed out - if you're not deaf - you'll hear it.
HTH
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Don wrote:

Vacuum leaks generally become less of a problem at full throttle as there's then less of a vacuum. I recently had poor running and it was the MAF - the air flow sensor. I guess if the car has knock sensors etc it could just be getting confused about they type of gas you've been giving it???
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snipped-for-privacy@yahoo.co.uk wrote:

I believe that's what I tried to tell him.. and it isn't that there is less vacuum at full throttle (although there is..) it's that the hole causing the vacuum leak is small compared to the open throttle body at full throttle. When the TB is closed - the vacuum leak may well equal the opening in the TB.
The knock sensors are not going to cause the car to get "confused".. this is a non-issue. They're there for exactly this reason - poor quality gas, and to optimize performance by allowing max advance for the fuel at hand.
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Hello All, I appreciate all the replies. **Note: Thru all this I've never gotten a check engine light, and the "stomp test" comes back clean. **Coils look good visually, verified battery voltage at all 6 connectors, and verified resistance of 0.6 ohms on all six. **I agree w/ Don about the car should still run with low octane, but knock sensors should retard timing and performance would suffer. I've been thinking for some time (even before it started running bad) that one or both knock sensors were bad, because I get lots of pinging when using low octane fuel, but I've never worried much about it becaused I normally use 93 Oct anyway. And I've never gotten a trouble code for the knock sensors. **I'm beginning to think something is keeping trouble codes from being stored???Is this possible? **I was thinking MAF also. I have a used MAF on the way from a salvage yard, should arrive tomorrow. **If that's not it, I'm thinking OXYGEN SENSOR. Car has 150,000mi - probably could benefit from a new one anyway. I will test as per Bentley, but even they say that the test won't be 100% conclusive with an exhaust gas analyzer. **If still no cure, I may break down at this point and go to the dealer for a diagnostic. **QUESTION- Could a clogged catalytic converter cause these symptoms? **QUESTION- Could all the crazy fuel additives and Oct boosters I ran for those 3 to 4 days have fouled the OxygSensor (or just pushed it into the grave it was already leaning over)?
Thanks for all the good stuff guys!!!!
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