<E28> Need Diagnostic Help.. 535i running rough

["Ron J" <ron@xxxxxxxxxxxxxxx>]

Hi All,

Well after a long drive back from Fort Myers FLA, and a good nights sleep, I
wanted to ask for some diagnostic help.  Here is the background.

I have recently replaced my Feul Pressure Regulator with a brand new Bosch
unit, due to rough idle, and engine missing during driving. It solved the
problems, and the car ran much better.  I have also replaced my ICV with a
brand new Bosch unit.  Both within the last 3 weeks.  The ICV was replaced
on New Years Day.

I drove all the way down to Florida with the new FPR (replaced before I left
here to go) and the car was fine all the way down except for the IVC getting
stuck everyonce in a while (I would pull over whenever it got stuck and tap
on it with a wrench and the car would stop the surging RPM and settle).
While I was in florida, the car was fine, save the ICV issue.  We drove to
Key West, all over the Everglades, into Fort Myers, Naples, and a few other
places.  No problems.  While I was there I decided to replace the ICV and
ordered a Bosch Unit from thepartsbin.com.  It took a few days to arrive and
I replaced the old one with the new and the surging idle/high idle went
away.   I thought this would have solved my problems, however it didnt.

On the way back the car started to behave strangely.  It initially started
when the car was idling.  It would stay at the normal idle speed, and then
all of a sudden on its own surge up to 1500 rpm, and stay there steady.  If
you tried to hit the gas the car would almost stall out.  Then the RPM would
settle down and the car would be fine.  Then in Kentucky I pulled into a
subway to grab a snack for our 6 year old passenger.  When we got back out,
the car wouldn't start, like it was out of gas, even though we had a full
tank.  I continued to turn the engine over and the car finally started up,
and we drove away.  Then while on the highway in 5th gear running at about
2000-3000 rpm doing about 70 mph, the car would start to stumble, like it
was either losing spark or running out of gas, and then catch again.  I also
noticed the fuel consumption guage start to act strangely.  Just before the
car would start to act strangely, the feul consumption guage would start to
climb up really high.  (The car has metric guages so its measured in
litres/100kms.  1 gallon is approx 3.8 litres, and 1 km is approx 0.6
miles. ) the guage would swing from a normal 9 ltrs/100kms to over 25/100,
and then the car would stumble.  This makes me think that the car is being
fed too much gas.  I dont know how that guage works, or what it measures for
its calculation.  But its saying that the feul consumption is way off the
chart whenever the stumbling starts.    The car would do this intermittently
all the way back to Toronto Canada.  Sometimes it would do this steadily for
10 min and the sometimes only 1 or two times in 20 min.  It wasnt
consistent, and the only precursor was the feul consumption guage.

Whenever we stopped I left the car running since I didnt want to have the
issue of a non start.  While it would sit there, the idle would be fine and
then jump up all on its own to 1500-2000 rpm and again if you hit the gas it
would almost stall out, unless you quickly let off.

this happened to me once before and it was recommended that it was my FPR,
so I have a new one, so I dont think its the FPR.  The stumbling during
driving is hard on the entire drive train since its jerky and immediate loss
of power and then just as immediate return, and sometimes its on and off a
few times in a few seconds, which resembles a jack rabbit start when someone
doesnt know how to drive standard.  So I know there is stress on the crank,
transmission, driveshaft, and rear end, among other things.

Is there anyone that can suggest a solution or offer any advice?

Cheers
Ron Jordan
85 535i
73 911s 2.7

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