Re: erratic idle?

[Dave Head <dhead@sundial.net>]

At 04:40 PM 8/16/97 +1000, you wrote:

>When I start the car up (only on cold startup) my idle jumps from
>800 to 1000 and vice versa it will do this until the engine warms up.
> Is my ISV hosed up????

Here's part of the deal...  Your system when cold is what's known as 'open
loop' on the FI - that means the FI works on a 'preset' FI pressure via the
warmup regulator and frequency valve, as opposed to 'closed loop'. In closed
loop the FI pressure is regulated by the O2 sensor input to the computer and
adjusted via the frequency valve.

The only other time the system goes open loop is at wide open throttle
(WOT), which is 2/3 throttle position.

An intermittent bad temp sensor would cause this, and could be seen by
hooking a dwell meter up to the test connection  behind the air boot. An
intermittent bad sensor or wire would cause the system to go from open to
closed loop when cold. The dwell meter would go from a constant value to a
varying value and back. You could even hear this via the frequency valve
buzz changing when cold (under fender, outboard of fuel distributor).

Another possible problem could be sticky ISV - but it would possibly be
sticky when warm, also. Wouldn't be the O2 sensor because its not inserted
into the system until warmed up.

********************************AUDI FAN***********************************
                                   EMCM(SW) Dave Head  
87 5KCStq 203K miles                1.7 bar 
    qcusa #3442                 Maitland, Florida   
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