[DML] Intermittent revving, Vacuum leaks, etc
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[DML] Intermittent revving, Vacuum leaks, etc

First off, thanks to everyone for links to the relevant docs when I posted  
about this 2 months ago.  I'm back with (hopefully) better questions, and  
a few new data points.  (and sorry for the late reply, but life has been  
getting in the way of hobbies lately ;-)

I've been paying a lot closer attention to what the car is doing lately.   
I've noticed that when the car is "behaving", it actually drives pretty  
well.  Most of the stuff I was talking about was related to when its  
severely misbehaving.  When I mentioned electronically adjusting the idle  
to match RPMs of the next gear, I actually was referring to normal  
up-shifting; when the car is misbehaving, as soon as I let off the gas and  
disengage the clutch, the engine RPM drops like a rock to about 300rpm in  
about 1/10 of a second, and then starts bouncing.  Normal manual-trans  
cars sort of "float" downward, making a nice smooth shift.

Anyway, I did have one really interesting event that will hopefully help  
diagnose this stuff: I was going about 40mph down a road, coming up to a  
stoplight, the engine was fully warmed up (just above the middle white  
tick mark on the temp gague) and so I shifted out of gear and coasted the  
rest of the way.  My foot was completely off the gas.  The engine was  
revving between about 500rpm to 1300rpm at one second intervals. (about as  
bad as it ever gets)  At the exact moment I came to a stop (a pretty  
gentle one, at that) the idle suddenly snapped to 750rpm and purred like  
the problem had never existed.  It drove perfectly fine after that.

Is there any part of the idle control that is based on actual vehicle  
speed?  I'm having a hard time imagining that a gentle stop is shifting  
something physical that starts or ends a vacuum leak. (with the Eibach  
shocks I get much worse physical shakes just from the roads).  Maybe its  
some kind of switch and just a random coincidence that it changed right as  
I stopped?

One other detail- I read that the entire engine is placed under vacuum so  
that the oil vapors get collected into the vapor canister.  My engine oil  
cover isn't very tight (I can wobble it around with my fingers while its  
fully seated).  Could that be a potential problem?

Also, I get a fuel smell in my garage overnight, but I've always assumed  
it was just the oil that leaks out the rear seal. (thanks to Prev Owner  
using super-thin synthetic in a 100Kmi car)  Is there some way I can test  
the vapor recovery system for leaks?  Could that even be the problem?

Mike Conrad
vin 5732


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