Re: Rattling under load, fluctuating idle (archive)

Don't worry about your cam timing. If you find out that your cams are worn down then I have a pair that has 29k miles on it, I swapped them for M3 cams. But I doubt that your problems lie with the cams.

Did you check the faulst codes? You mentioned that when you switched the DME the car was fine for two days. Two days is wnough time to learn fault codes so I would check that first.

What kind of oil are you using? Change the grade of oil depending upon your temperature and how you use the car. You mention that you notice these symptoms under load or when going uphill. Are you taking the car hard? Remember that your car doesn't have a big engine. So the symptoms of sulfer smell, idle fluctuation and sluggish is normal. First, the sulfer smell is normal in any car where you take the engine hard. Second, if the engine is taken hard then the oil is hot(oil pressure is also used to activate the vanos), so this can affect the idle. Does the idle fluctuate whe the engine is not hot? Third, you mention sluggish. If the engine is getting hot maybe the Aux fan is engaged, so this robs power from the engine. All these symptoms can improve by selecting a different grade of oil, it may not get rid of them, but it will help.

Finally, you mention that the power doesn't start going until 3k rpm. That is normal. That is how the power band is. The rattling sound, can you describe where it comes from. Are you sure it is not a ticking noise? Under hard driving the fuel injectors can tick, then go away.

All your symptoms shouldn't be a problem unless they happen all the time, under different driving conditions and outside temperatures. What surprises people is that a Jim C (or equivalent)chip helps with these symptoms too.

:)Mark J
'93 525i, custom intake, M3 cams, custom Autothority chip, lightweight flywheel, S52 fuel injectors
P.S.
If I am wrong about all of this, then check your clutch and throw-out bearing.

I'm trying to fix a recurring problem on my '95 525i. The engine rattles under load, especially when going uphill at RPMs less than 3000. Occasionally the idle will fluctuate when coasting to a stop, between 500 and 700 RPM. Also, the car feels somewhat sluggish, especially when the idle problem is occuring. Finally, the exhaust often smells of sulfur when the car is driven hard. The car has 45,000 miles on it, and has a manual transmission.

In trying to fix the problem, I've done the following to the car:

Replaced the spark plugs.
Replaced the engine coils.
Had the fuel injectors cleaned.
Replaced the idle control valve.

I've also tried replacing the DME. That fixed the problem for two days, after which it returned, as bad as ever, so I swapped back in the old DME. That was especially frustrating, as I thought I'd finally tracked down the problem.

I'm thinking about replacing the O2 sensor next, though the local BMW dealership tested mine and claimed it wasn't causing the problem. Other possibilities I'm considering: the air flow sensor or the knock sensor.

Any ideas out there? Anyone have the same problem and fix it?

Follow Ups:

Re: Rattling under load, fluctuating idle Jess G. 00:35 8/13/2001 (1)
- Try driving slower car for 2 days then go back :) Mark J 00:50 8/13/2001 (0)

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