The O2-sensors were suspects all along.
When my O2 sensors were running too cold, the result was an unstable
idle; it romped up and down something fierce. Yours isn’t doing
that. But the systems are different enough that, I suppose, the same
issue could cause a different symptom in your car.
The reason Mr.
Bywater disabled the periodic hot air injection was the
speculation that this is what causes the rolling idle. It did
not help.
Interesting. The rolling idle has a period of every couple of
seconds, does it not? How often would you think that thing would
turn on the air pump to test the O2 sensors? I wouldn’t think it’d
be THAT often.
I’ve tried three different brands O2 sensors in 4 years (and
less than 10,000 miles) – no luck.
No luck on what? The rolling idle, or the shift in idle speed when
you put it in gear?
Does your ECU still have an idle mixture adjustment like the 6CU and
16CU did? Because if so, I’d expect adjusting that to be your best
bet toward correcting that rolling idle.
…but I was hopping that
someone what be able to share some ideas.
OK, I think I may have come up with an idea. As I understand it,
the fuelling maps that are built into these ECU’s concentrate on the
idle and near-idle realm, since it is more difficult to get the
fuelling right in that realm than at the higher power conditions.
Let’s presume that there are several points on the map in the
vicinity of 750-900 rpm. And when you first start the car, it
settles on a point that gives 750 rpm at the idle setting. Then
let’s presume that, when you shift it into gear, the additional load
causes the engine to react, and in reacting it moves to a different
point on the fuelling map – and this point, by virtue of different
fuelling (probably leaner, I think leaner generally speeds up idle)
runs the engine at 800-900 rpm with the exact same idle setting. If
the engine could be moved back to 750 magically without changing the
manifold vacuum or throttle position, it might resort to the original
mapping point and idle at 750 once again – but I dunno how you’d get
it there other than to come UP at it from the starter rather than
down to it.
That would imply that it’s the mapping itself that’s causing this
idle issue. A difference in fuelling at 750 rpm vs. 850 rpm, with
all other variables being equal.
You mentioned that Bywater has been tinkering with your ECU. That
may explain why you’re the only one experiencing this. If Bywater
revised the fuelling maps, perhaps he inadvertently caused this.
I think you can test this theory. Manually adjust the idle speed
up to 900, and I mean 900 when the car is first started. If you can
then put it in gear and take it back out of gear and the engine
resumes running at 900, we’re on the right track. Moving the idle
speed away from these troublesome points on the map cleared it up.
OTOH, if you put it in gear and take it back out of gear and the idle
ends up at 1100, we’re probably barking up the wrong tree here, just
set the idle speed back where it belongs and fuggetaboutit.
I suppose another idea might be to set the idle speed DOWN to
something below 750, like say 600. See if it resumes 600 after
shifting in and out of D. If the troublesome data point is at 750,
presumably the lower idle setting would pull it back down to 750 even
after shifting in and out of D, which means it’d go all the way to
600. So, same test: If the engine resumes 600 after playing with
the shifter, we’re on the right track. If it idles somewhere faster,
like 750-800, the theory gets pitched and we move on.
– Kirbert
// please trim quoted text to context onlyOn 21 Sep 2014 at 18:30, sbobev wrote: