[mkiv] P1652 Error w/Low Vacuum and Boost

[Harris, Damon (Washington)]

Steve,
 
My compressor died on me a few weeks ago but I'm familiar enough with the intake pressurization test to knock it out at a gas station in a couple minutes so I'll give it a try.
 
Thanks,
Damon
 
 

________________________________

From: mkiv-bounces at mkiv.com on behalf of Steve V.
Sent: Fri 7/29/2005 12:30 PM
To: 'The MKIV.com National Mailing List'
Subject: RE: [mkiv] P1652 Error w/Low Vacuum and Boost




Pressurizing the entire system typically finds leaks.

Put a Schrader (tire) valve in a strong soup can and then clamp it inside
the turbo intake hose.  Then pressurize with your air compressor.  (Be
careful that the pressurized can can shoot out like a bullet if it gets
loose.)

Steve

----
Steve V. | 1997 6spd T61 | http://www.moreboost.org  

> -----Original Message-----
> From: mkiv-bounces at mkiv.com [mailto:mkiv-bounces at mkiv.com] On
> Behalf Of Harris, Damon (Washington)
> Sent: Wednesday, July 27, 2005 3:53 PM
> To: mkiv at mkiv.com
> Subject: [mkiv] P1652 Error w/Low Vacuum and Boost
>
> All,
> 
> For the past six months or so I've been getting a recurring
> CEL which always turned out to be P1652 (Idle Air Control
> Valve Control Circuit).  Because the car was idling and
> running well and the CEL only popped up once every month or
> so, I did the lazy thing and just reset it until something
> worse happened.  Now it's worse...
> 
> The CEL comes on for P1652 almost every time I start the car
> and my vacuum reading on my boost gauge has dropped from 22
> inHg to around 18 at idle.  At WOT my boost drops steadily
> from 17psi to 14psi where before it consistently held
> 17-18psi to redline, even in warm temperatures.  Naturally
> the car feels like a slug up top even though part throttle
> performance is still quite good and the car idles normally
> with no surging or stumbling.  My wideband shows normal AFRs
> (10.9-11.2) at WOT in 3rd and 4th gear.
> 
> Thinking I had some sort of vacuum leak through the IAC, I
> first tried cleaning then replacing it as well as the
> associated gasket, washer and check valve.  The idle vacuum
> is slightly better (20 inHg) but WOT performance is still
> poor with boost dropping off as revs climb.
> 
> I did a cursory vacuum hose check and everything looks
> connected while a quick soapy water spray on the hoses didn't
> turn up anything either.  I'll go through things a little
> slower tomorrow when I have more time.  My questions to the list are:
> 
> 1) Has anyone seen this issue before?
> 2) What criteria does the ECU use to trigger the CEL for P1652?
> 3) Can anyone suggest some reasonably simple vacuum leak
> checking methods?
> 4) Does it sound like I'm barking up the wrong tree and
> should turn my attention elsewhere?
> 
> Thanks,
> Damon
> 97TT BPU+
> 
>
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