<E28> Strange hesitation on long drive & Idle

["Ron J" <ron@xxxxxxxxxxxxxxx>]

Hi All,

I just returned an hour ago from Montreal Canada, back to Toronto Canada,
where I live.  Its about 5 hours @120 kmph, or around 75 mph.   Which is
about average speed on the highway that goes there.    I on the otherhand
average about 140 kmph / 90 mph.  Anyway down to the issue that popped up.

The car is an 85 535i <E28> with the M30 Engine.  No real mods except a K&N
Filter, and Free Flow exhaust cat back.  The car has run fine for 2 weeks
since the exhaust was modified, so I don't think its the problem.  The
problem started when I got to Montreal and pulled into a McDonalds at around
1:30am (first stop since we got on the road).  I was sitting in qeue waiting
for the food, and noticed a bit of an rpm hesitation, but not surging.. more
like a bit of a change from about 600- 700 and then back down, bit of
roughness, Pulled forward, got food, and then went to pull away, and the car
stalled dead.  Tried to start it, and it wouldnt.  The starter turned, had
full power, all dashlights there, then it would catch and barely stay idle,
and when you hit the gas it would die out.  After a few tries, it started up
fine, and didnt do it again until the next day, oddly enough in the same
mcdonalds drive thru ( Wonder if the car is telling me something about
Mcdonalds Haha.. ) So same thing hard start, then when it caught it was
fine.   I gassed up last night, checked into a motel, and slept.  Then this
morning when I left, and got on the highway, about 3 hours into the drive, I
noticed a bit of a miss, or hesitation, when I would let off the gas and let
the RPMs drop a bit.  I was almost always in 4th or 5th with RPM at about
2500- 3500.  Then the problem started to get worse, and when you gave it
gas, it would hesitate, like it was running out of gas, or spark was a
problem,  If I put my foot to the floor, it would bog a bit and then catch
and rev out fine, and accelerate fine, and behave normally for a while, and
then again it would start the same thing.  Missing, Hesitiating, poor
accelaration and then it would even out.  It happened once when I tried to
overtake a truck with another car close behind.  I got a bit worried and a
crunched rear bumper was coming to mind.  I was thinking that the gas I
bought might have been bad, so I pulled into a gas station about 1 hour
later, and gassed up with premium (93 octane) and added some injector
cleaner.  When I started the car again it started fine, and was a bit rough
so I gave it some gas, and it seemed a bit smoother.  I pulled around to the
rest stop area, and went in to use the washroom, and when I cam out, it
wouldnt start again.  All power, etc, just wouldnt catch.  Then when it did,
it would idle rough at about 400 rpm, and if you gave it gas it would die.
I finally got it started and let it sit at the rough 400 rpm, and it
eventually evened out at went to normal idle.  Gave it a few shots of gas,
and it seemed fine.  Got back on the highway, and got all the way home, lots
of power, no hesitation.  When I got home and started to empty out the stuff
in the trunk into my garage, and tried to start it again to pull around to
the front of the house it wouldnt start again.  Lots of crank, lots of
power, just no catch.  Then after a few attempts ( 7 or 8) it caught again,
and reved fine, no hesitiation etc.  I pulled around to the front of the
house, parked it, shut it off, and then turned the key again, and it started
right away and purred happily.    So I really don't know whats up..

A few possibilities.

1.  bad gas from Montreal.
2.  rain on the trip there, got the wires damp, though that has never
happened before, and didnt cause any issues yesterday during a downpour
while I was driving, and only seems to happen after a few hours of driving
3. Sticky ICV valve ( been cleaning mine out with Carb Cleaner for a few
months since the last issue of stalling at idle. reason: I am a recently
returned University mature student on a budget)
4 Dirty fuel filter ( though I think not due to the intermittent issue)
5 problem with the ignition coil.  Maybe it has an intermittent problem??

Anyway, I think I should change the plugs right off the hop since it needs
it anyway.  But has anyone experienced this issue before?  Could it be the
ICV doing this, even when the car is warm and driving?

Oh, aside from this issue, I certainly surprised a few preludes and jettas
on the way home, by steadily pulling away from them on hard acceleration
 while the car was behaving) while loaded with me, my girlfriend and her
son, as well as a rottie, and all the luggage that accompanies a long
weekend in another city :)  I loved the astonished look on thier faces in my
rearview :)  What a fun car to drive !!

Please advise, or offer any ideas
Thanks
Ron Jordan
85 535i
73 911s

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