Re: new o2's but still get check engine. (archive)

I have been chasing the check engine light for 2 years without success. Here is a call for help I placed last year, looking for some advice. I hate to ruin your day, but this is the most frustrating problem i have ever faced....
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I have a 94 740i (E32). I have owned it for almost 3 years. I bought it at about 55,000 miles, it now has about 83,000 (I am now at 91k).

Here is the saga. For about the last 24 months there has been a nagging problem that 4 different mechanics (2 of them dealers), and about $3000, have not been able to fix.

There are 2 different indicators, but I think they are related.

First, on mornings, when the temp is below 70 or so, at first start, the car runs fine. After about 5 minutes, at the first stoplight I come to, the car will be idling fine, then out of nowhere, there is a stumbling of the idle, the Check Engine light illuminates, and the car idles very poorly. Occasionally even dies. Starts right back up, but the idle is still poor. The car will continue to run roughly at idle, the check engine light will stay on for maybe just a few seconds after starting to accelerate, maybe stay on for 2 days. Then the light will go out, the car runs fine, til the next morning. Or not. Maybe the car will run fine for a day, or a week.

The second indicator, occurs after the car is at normal temperature. During deceleration, when the RPMs are dropping from 2000 down to about 1000, the Check Engine blinks (chatters) and sometimes the car thunks into Limp Home Mode. Stuck in 4th gear. After stopping, shutting down the car for a couple minutes, the tranny is fine, and the chattering may or may not throw it back into limp mode.

The most irritating part of this problem is that it is not consistent. the car may run beautifully for a couple weeks, no problems. then the next morning, bam, light and rough idle. Same with the limp mode. Won't happen for days, then happens 3 or 4 times in one trip.

The computer always indicates bad O2 sensors (#2 more often thatn #1) when this has happened. And sometimes the mass flow sensor as well.

The following things have been replaced, mostly by certified mechanics, some by me:

3 sets of O2 sensors.
3 new mass flow sensors.
Intake manifold gaskets.
Front intake cover gasket.
Oil separator.
Idle control valve.
Crankshaft position indicator (2 times).
New plugs.
Tried new computer unit, no difference, put original one back in.
Fuel pump.
Fuel filters.
Chemical cleaning of injectors.

I am sure I have left out some things that have been tried here, but you get the idea. I am of the opinion that it is a vacuum leak, but the only thing left to change are the head gaskets, and I think I would have some leaks out if they were bad, and they seem pretty tight.

My problem right now is that I just moved to a new place, with a new dealer, that will want to start all over with the O2 sensors and the mass flow sensor. Back to ground zero.

HELP!?!?!?!?!
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See how much fun I have had with my check engine light? heh heh

Michael

Follow Ups:

Re: new o2's but still get check engine. Steve L 00:45 4/30/2002 (2)
- I had it and fixed it easy money Dan DeSmet 08:53 4/30/2002 (1)
  - Thanks! I'll try it next week! Steve L 12:05 4/30/2002 (0)

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