[T3] Cold idle Problem
dave at hallvw.clara.co.uk
Thu Jul 21 04:57:03 PDT 2011
The AAR valve acts like a fast idle mechanism on a carb by providing a
temperature variable air-bleed into the intake air distributor (IAD). The
ECU senses the intake pressure, and because the extra bleed air acts like a
partly open throttle valve, the ECU adds extra fuel for the extra air to
keep the mixture right. As the engine warms up, the AAR closes off and the
idle goes back to normal.
If it runs well at higher rpm, it might simply be the battery voltage is a
bit on the low side due to a sticking voltage regulator. Is the battery
well charged and the charging voltage around 14V at medium rpm?
UK VW Type 3&4 Club
From: type3-vwtype3.org-bounces at lists.vwtype3.org
[mailto:type3-vwtype3.org-bounces at lists.vwtype3.org] On Behalf Of SCS
Sent: 21 July 2011 06:41
To: type3 at vwtype3.org
Subject: Re: [T3] Cold idle Problem
Thanks for the suggestion, but again, if I had a bad electrical connection,
it seems it would run lousy when I revved it up. I've got good compression
and the car runs well except at cold start up.
Actually, Bobsnotch seems to be on to something. Reading up on the AAR, it
supplies extra air to a cold engine to match the extra fuel supplied by the
ECU. If the AAR is malfunctioning, there wouldn't be enough air to match the
extra fuel. This would create a rich condition until the engine warmed up
enough to make the ECU reduce the volume of fuel.
Although this seems reasonable, I do not notice black sooty exhaust when the
idle is acting up.
On 7/21/2011 12:08 AM, Jim Adney wrote:
> On 20 Jul 2011 at 23:55, SCS Crewcab wrote:
>> OK, but, if it's caused by either of these problems, wouldn't it also
>> run lousy when I revved it up?
> Yes. If it's only at idle that it runs poorly, then I'd check
> compression; it doesn't sound like a FI problem. That makes me wonder
> if you've got a bad cylinder. You can test that by pulling one SP wire
> off the dist cap at a time.
>> Is there anything on the Type 3 FI system that performs the same
>> function of the choke on a carbed car?
> The temp sensors work with the brain to adjust the richness according
> to the head and air temps.
> There's another FI possibility. It's possible that you're not getting
> good electrical connection at one or more of the injectors. Try
> pushing those connectors sideways while idling to see if that changes
> anything. If it does, you'll need to back the connector pins out of
> the plastic bodies, snug them up very carefully, and reinstall them.
> Replacement injectors came with very slightly thinner pins, and this
> sometimes catches us. I don't recall if it causes your particular
> symptoms, but it does cause rough running. The best way to diagnose
> this is with the Bosch tester, but try the test above.
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