[mkiv] P1652 Error w/Low Vacuum and Boost

[Steve V.]

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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