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IMT valve

  #1  
Old 07-16-2010, 10:33 AM
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Default IMT valve

I'm wondering if the IMT valve is a part of the emission system?
What would be the consequences of a malfunctioning IMT valve?
Does a failed valve trigger MIL (codes)?
Any test procedure one would recommend?

Thx,
 
  #2  
Old 07-16-2010, 09:03 PM
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For my 2000 VW Passat 2.8 (ATQ), it's listed as an emission system and triggers code 17562 (P1154), but scanners call it a Fuel/Air metering problem...which it really is not (in my opinion). It's just an adjustment of the length of intake tubes to help extend torque at higher rpms...a performance feature. I'm not a scientist...so it may effect emissions, but I don't see how.

In any case, It only triggers the code if it's any electrical problem with the valve (with my VW). I've found these systems to be prone to mechanically seizing , due to a lubrication loss on the control tube inside the manifold, which is really not serviceable according to Audi/VW. The 2 stage on my VW seized in place and triggered no code...AND on the 3 stage unit in my '01 A8 (AUX) both internal tubes seized in place (stuck in low rpm range) which is very common and most people don't notice...I found it on visual inspection. I DID manage to free my up with a delicate, unorthodox procedure, not recommended by Audi.

The Bentley manual for D2 A8's does NOT list a code for IMT malfunction, BUT includes an electrical signal check of the valve with VAG OBD in "Output Diagnostic Test Mode" (DTM)...followed by a test to see if valve "clicks" when voltage is put to it.

I don't have VAG, so I did a more direct test to isolate the problem. I had already found that vacuum controls were NOT actuating properly with engine off, on , low, mid or high rpm, etc. So, I popped off one end of the little ball-joint linkage arms from vacuum pods to the spring loaded levers which move the internal changeover tubes in the manifold. I then turned the engine on and off...both vacuum pods retracted (engine on) and then could be re-inflated with engine off. I even had a helper rev the engine to the points that each vacuum pod is supposed to actuate and they worked correctly. Conclusion: IMT valve(s) OK...mechanical problem.

While the linkages were disconnected, (with engine off) I manually turned each lever connected to internal changeover tubes which should "open" smoothly (with resistance of spring tension only) and smoothly snap back closed easily under their own spring tension. They did not (I could move them, but with much more effort than spring tension or vacuum pods could provide)...mechanical problem...not a control problem.

This was exactly the same case with my VW, which has only one manifold control tube...no electrical or vacuum problem.

My repair method had to be done twice to free up parts and my method was NOT intended by Audi...their only solution is to replace entire manifold as a unit.
I touched on my repair (on a 3 stage '01 A8) in post #4 of this thread:

http://forums.audiworld.com/showthread.php?t=2786415
 

Last edited by silverd2; 07-20-2010 at 08:04 PM.
  #3  
Old 07-19-2010, 11:31 AM
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Very helpful info.

Thank you
 
  #4  
Old 07-20-2010, 06:01 PM
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Yeah those stupid plastic arms for the intake manifold changeover valve always break, it wouldn't cause you to not pass SMOG though, maybe affect performance in a given powerband. There is a company that make aftermarket metal arms but i have no idea who they are..I have just JB welded the bastards back together.
 
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