M30B35 rough idle, no acceleration

Specific conversations and info for the BMW E28 M5 and M535i.
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bavblue
Posts: 527
Joined: Aug 15, 2006 6:36 PM
Location: Sun Diego, Ca

M30B35 rough idle, no acceleration

Post by bavblue »

Hello, I am asking for friend of mine. He has 535i 1993, I believe it was one of the latest year M30 was in production, since it has electronic throttle body and idle control valve. Car ran fine until recently, when check engine came up, we ran code reader, it was showing O2 sensor, so we got OEM and replaced it, also deleted all faulty codes, car starter, idled a little better, but it has lack of any power whatsoever, long story short he mentioned that he had engine out to reseal it, he also mentioned that we pulled timing cover to to install new rail guide. I am suspecting that he moved timing, but before I dig into it I am not sure about electronic throttle, never had one, is there anyway to test it ? I checked for vacuum leaks, all good, cap rotor, plugs and wires are all new.
RobertRO
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Joined: Feb 12, 2006 12:00 PM
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Re: M30B35 rough idle, no acceleration

Post by RobertRO »

From my exprience, a technical problem of a car may be generated either:
1. by a single event, if the car ran fine before that event, and poor right after the event. Think of that event as a kind of an on/off switch that suddenly triggers the problem,
or:
2. by wear. In this case, the technical condition of the car slowly degrades over a longer time / miles interval.
Usually, problems caused by a single event are much easier to diagnose than those caused by wear.

Based on your post above, I believe that you are in scenario "1".
If the car ran fine before the engine reseal job, and then immediately started to be letargic afterward, then it is very likely that the technical problem was generated during that job. I would carefully check all the engine components that were touched during the reseal work. Timing is very likely to be the culprit.
The fact that, by replacing the O2 sensor you slightly improved the idle, I don't think it's connected to the lack of power issue. You simply discovered a totally different problem, that was caused by wear.
tn535i
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Joined: Jul 14, 2006 1:30 PM
Location: Middle Tennessee

Re: M30B35 rough idle, no acceleration

Post by tn535i »

I would NOT assume timing and there are ways to check that without pulling the timing apart again. More likely case might be malfunction or no function of the et/b now. Poor connection or broken wires during the work done? You should be able to see hear motion of the et/b in some way to confirm.
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