I thought I should summarize what I've been through with the intake manifold on my 2004 V8 Touareg. If you're reading this then you probably know roughly how it works. There are two flaps that move inside the manifold and vary the geometry so that it's optimized for various rev-ranges. These flaps are activated by cranks, rods, actuators solenoids and vacuum, all of which can go wrong. Most serious is probably the rods seizing inside their pivots and the best place to read up on this is here on SilverD2's excellent DIY on how to free-up the flap-rods that run through the manifold. (Also a nice intro on why VW bothered with this stuff)
40V Intake manifold fix for stuck or sluggish flap pivots (no broken parts)... - AudiWorld Forums
This was all kicked off by the engine-check light coming on and the following codes being read
17831 - Secondary Air Injection System; Bank 1
P1423 - 002 - Insufficient Flow - MIL ON
17819 - Secondary Air Injection System; Bank 2
P1411 - 002 - Insufficient Flow - MIL ON
Often you read that these codes are caused by the secondary air-pump, located under the passenger-side headlamp, that's gone bad - but mine seemed to be blowing like it should and all hoses looked good
There's also a tech-bulletin that mentions these codes here:
http://www.clubtouareg.com/forums/attachment.php?attachmentid=2469&d=1187713269
The engine cover can cut through the vacuum line near the N112 valve and maybe snap the nose off the valve - I modified my cover as it suggests, but my N112 valve worked and no tubes were cut.
So then I started to look at all the 'stuff' at the front of the manifold. The thing to check first is whether the vacuum actuators do anything immediately after you start the engine - as described in SilverD2's Audiworld DIY. Mine didn't move at all - working out why I found I had 5, yes five!, things wrong with the system. Take a look at this diagram...
Intake system vacuum system throttle valve control unit 4.2ltr.. Fits: Volkswagen (VW) | Jim Ellis VW Parts
1) Both solenoid valves (item 11 on the diag.) had failed
2) The check valve (part of Item 10) didn't work and the hoses were split in multiple places
3) There was a leak in the tube (Item 12) at the connector where it meets item 33 - so no vacuum reservoir
4) the push rods that turn the flap-rods - one was cracked and one was broken in 2. Buy new, better ones here:
gruvenparts.com - Billet / Composite 4.2L V8 Intake Manifold Linkage Arms
5) the flap rods were stiff as described above by SilverD2.
Numbers 1 thru 4 are basically sourcing parts and replacing them, easy - number 3, I must admit I just wrapped it in tape to re-seal it because it's $80 for a plastic tube. Number 5 needs some real work. I followed SilverD2's audiworld post pretty closely - I would add the following to his write-up.
- Definitely, definitely get a puller so that you can pull the housing off the rod - that way the rod is more likely to stay in the socket at the rear of the manifold - I never had to fish mine back in because they never came out - but I hear it's really tricky, but do-able.
- Buy a set of mini-brass brushes for your dremel tool - you have to really polish the housing bore to free up the flap rods. This is plastic on metal and it needs to be smooth. Grease them up with silicone. Don't try to re-assemble it until it's really super clean and shiny - if you do, and it's still stiff, then it all has to come apart again with the puller with added risk that the flap-rod comes out of the socket.
- Do the top one first, put it back together, then do the lower one - don't get in a mess with both apart at once (as SilverD2 suggests but I want to emphasize)
- test that you're good to go by putting the crank arms back on without the return springs and test for free-spinning rods - they should almost fall back to vertical under gravity.
After i changed all that the actuators worked immediately after startup as they should - and the difference in torque was instantly obvious - very snappy off the line now. The power-steering seemed more 'assisted' now as well but maybe I imagined that. Apparently Bentley doesn't say anything about fixing these flaps and VW's response is just to sell you a new manifold - crazy. Definitely worth checking that this is all working if only to make sure you're not wasting gas.
-Richard
40V Intake manifold fix for stuck or sluggish flap pivots (no broken parts)... - AudiWorld Forums
This was all kicked off by the engine-check light coming on and the following codes being read
17831 - Secondary Air Injection System; Bank 1
P1423 - 002 - Insufficient Flow - MIL ON
17819 - Secondary Air Injection System; Bank 2
P1411 - 002 - Insufficient Flow - MIL ON
Often you read that these codes are caused by the secondary air-pump, located under the passenger-side headlamp, that's gone bad - but mine seemed to be blowing like it should and all hoses looked good
There's also a tech-bulletin that mentions these codes here:
http://www.clubtouareg.com/forums/attachment.php?attachmentid=2469&d=1187713269
The engine cover can cut through the vacuum line near the N112 valve and maybe snap the nose off the valve - I modified my cover as it suggests, but my N112 valve worked and no tubes were cut.
So then I started to look at all the 'stuff' at the front of the manifold. The thing to check first is whether the vacuum actuators do anything immediately after you start the engine - as described in SilverD2's Audiworld DIY. Mine didn't move at all - working out why I found I had 5, yes five!, things wrong with the system. Take a look at this diagram...
Intake system vacuum system throttle valve control unit 4.2ltr.. Fits: Volkswagen (VW) | Jim Ellis VW Parts
1) Both solenoid valves (item 11 on the diag.) had failed
2) The check valve (part of Item 10) didn't work and the hoses were split in multiple places
3) There was a leak in the tube (Item 12) at the connector where it meets item 33 - so no vacuum reservoir
4) the push rods that turn the flap-rods - one was cracked and one was broken in 2. Buy new, better ones here:
gruvenparts.com - Billet / Composite 4.2L V8 Intake Manifold Linkage Arms
5) the flap rods were stiff as described above by SilverD2.
Numbers 1 thru 4 are basically sourcing parts and replacing them, easy - number 3, I must admit I just wrapped it in tape to re-seal it because it's $80 for a plastic tube. Number 5 needs some real work. I followed SilverD2's audiworld post pretty closely - I would add the following to his write-up.
- Definitely, definitely get a puller so that you can pull the housing off the rod - that way the rod is more likely to stay in the socket at the rear of the manifold - I never had to fish mine back in because they never came out - but I hear it's really tricky, but do-able.
- Buy a set of mini-brass brushes for your dremel tool - you have to really polish the housing bore to free up the flap rods. This is plastic on metal and it needs to be smooth. Grease them up with silicone. Don't try to re-assemble it until it's really super clean and shiny - if you do, and it's still stiff, then it all has to come apart again with the puller with added risk that the flap-rod comes out of the socket.
- Do the top one first, put it back together, then do the lower one - don't get in a mess with both apart at once (as SilverD2 suggests but I want to emphasize)
- test that you're good to go by putting the crank arms back on without the return springs and test for free-spinning rods - they should almost fall back to vertical under gravity.
After i changed all that the actuators worked immediately after startup as they should - and the difference in torque was instantly obvious - very snappy off the line now. The power-steering seemed more 'assisted' now as well but maybe I imagined that. Apparently Bentley doesn't say anything about fixing these flaps and VW's response is just to sell you a new manifold - crazy. Definitely worth checking that this is all working if only to make sure you're not wasting gas.
-Richard
