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Re: 86 5kCSQ jerks when deacclerated

Intisar Husain wrote:

> The normal scenario for the jerk is while I am going around 20MPH,
> in 2nd gear, bar about 0.4 to 0.7, and if I take off the foot completely.
> My car idles around 1250 RPM, I am not sure if it is normal.  I have
> ordered the service manual, and will look into this.  By the way
> what is decal bypass?

The deceleration bypass valve is a system that allows the metering
plate of the fuel injection system to fall back quickly to the idle position
when you are coasting along with the throttle closed.  It responds to the
"closed" signal from the idle/WOT switch and the engine RPM, as Steve
wrote.  Basically it just bypasses the metering plate.

My car does the same abrupt thing unless I am gentle with the throttle at
slight throttle openings in the lower gears, but it's not so severe as to
make me fear getting hit from behind...I've adjusted to it and now I rarely
ever find myself causing it except when I'm creeping along and
someone unexpectedly slams on their brakes in front of me, which is

1250RPM is definitely a high idle when the engine is warm.  Mine ticks
along at about 900 on the tach.

And no, the '86 model does not have the throttle dashpot.  I believe this
was introduced in 1987.  I recall posts with pro and con sentiments
because it "interferes" with the engine's slowing down somewhat
when you abruptly close the throttle...maybe the next time I'm out
scrounging I'll see if I can find one, install it, and report back.  At the very
least, it should help tame any big pressure spikes under high boost,
albeit not as effectively as a real, Quattro-List Turbo Bypass Valve (tm)
setup :-).