[V8] 5spd throttle body questions

Fri Jan 23 08:59:42 PST 2009

Hi Steve, thanks for the feedback.

I agree that the operation of the dashpot has no bearing on my high idle
issue.  However, I have always hated how the engine rpm hangs in between
shifts, so I will be adjusting it.  I adjusted a little already, but not
enough.

I believe I have isolated the cause of the high idle and if so, it is indeed
a vacuum leak.  I went full bore on troubleshooting yesterday, went over the
throttle body, cleaned and lubricated, and made sure it's operation was
smooth and unimpeded.

I cleaned up the fancy rubber gaskets and used a torque wrench and the
proper seqence from the service manual to reassemble the whole throttle body
area.  

I pulled both vacuum hoses in front (they both go to the carbon canister
valve) and plugged those holes and found no difference.

I went to the back of the engine and replaced the hose that loops up over
the intake opening, connecting the intake manifold to the block.  I have
fought with this one before and the existing hose was hard and the
connections were loose.  This also seemed to have no affect on the high idle
issue.

The hose that provides vacuum to the climate control system was a little
loose so I added a hose clamp, one that is smooth all the way around inside.
I recall now that I did not remove this hose and plug the fitting to
completely rule it out as a possible leak.

However, it was at this point that I started spraying aerosol cleaner around
various areas to inspect for leaks.  This engine was apart before I bought
the car 10 years ago and I have little confidence in anything based on the
low level of workmanship I have found in many areas and instances.  So I
have doubted almost everything, including any/all sealing of the intake
system.

When I sprayed a good dose of cleaner down in by the front breather hose,
the one that disappears under/inside the intake manifold, the engine almost
stalled.  

Now, I assume that means the front breather hose is toast, which wouldn't
surprise me because I have never replaced it and I have no reason to believe
that anyone else has either.  There is still a small amount of doubt about
the sealing of the intake manifold coincidentally in that area, but I will
go after the hose first and on general principle since I have avoided it
much the way one avoids the dentist for fear of what might be found.  

So, is it possible to replace this hose without removing the intake
manifold?  I realize that may not be easy, but is it impossible?

Conversely, how big a deal is it to pull the intake manifold?  I assume
having new seals/gaskets on hand might be advisable.  Ultimately I'd prefer
to avoid this like the dentist, but you gots to do what you gots to do.

I'm going to proceed in trying to replace the front breather hose w/o
removing the intake manifold.  I believe I can just get some more of the
same kind of hose I used to replace the top breather hose.  I don't think
the bend in this one is that critical that it would present a problem.  

Thanks for all replies,
Ed

> -----Original Message-----
> From: v8-bounces at audifans.com 
> [mailto:v8-bounces at audifans.com] On Behalf Of urq
> Sent: Friday, January 23, 2009 12:43 AM
> To: 'q - V8'
> Subject: Re: [V8] 5spd throttle body questions
> 
> 
> AFAIK the dashpot is in effect an emissions control device 
> ... the MT cars have it because they are often operated at 
> high manifold vacuum (throttle lift during shifts) which 
> causes high NOx.  It gives the engine RPMs a chance to drop 
> before the throttle plates completely shut.  
> 
> Since #2 has an engine intended for an AT car the TB has no 
> dashpot.  I have noticed no functional difference on #2 as a 
> result of having no dashpot. It's a good thing that quattros 
> don't get smogged on the dyno though ... the lack of dashpot 
> might cause high NOx at shifting.  
> 
> My tuppence on the high idle problem is not to worry about 
> the dashpot or trying to adjust it ... I agree that the 
> problem is likely to be related to the vapor recovery system. 
>  There's supposed to be a solenoid which closes the path to 
> the intake from the carbon canister. ISTR reading that you 
> were able to draw air from the canister ... is perhaps the 
> solenoid remaining open and allowing air into the engine 
> bypassing the throttle body?  One of the output checks the 
> ECU has opens and closes the canister valve, you may want to 
> run this to see if you can hear the valve clicking open and shut ...
> 
> 
> Steve B
> San Jose, CA (USA)
> 
> -----Original Message-----
> 
> I had one of those inuitive mornings where you fix things in 
> your mind as you are slowly waking to concsiousness.  I 
> remembered that the 5spd cars have the dashpot to aid in 
> engine rpm control during shifts.
> 
> Is there any difference other difference between the 3.6 and 
> 4.2 cars? Venturi diameter, etc?
> 
> Also, I seem to recall that someone has used a non 5spd TB on 
> a 5spd car and reported no real difference or trouble 
> shifting.  Was that you Steve Buchholz?
> 
> I've been paging through etka and realizing/remember just how 
> simple these are when compared to a turbo 5.  There's like 
> five vacuum lines and 3 breather hoses.  That's it.  Any 
> other vacuum leak would have to come from something more 
> troublesome like a bad seal on one of the parts of the intake 
> manifold or throttle body.
> 
> Still trying to find some info about adjusting the dashpot.
> 
> Ed
> 
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