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Hello all - seeking advice. I took my car's IAC valve out the other day. It was almost completely black (dry black, not wet oily). It's a 2001 2.5, about 94000 miles, recently had the HG and exhaust done. I've cleaned the valve and reinstalled, but would like any ideas on what causes such blackness? It was also very black inside the throttle body, which I wiped out with paper towel.
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Greenmamba
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It is soot from exhaust gasses sent back through the EGR path for emissions purposes. It is a normal condition. Cleaning is a good idea once in a while.
 

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Actually, it oil soot from the pcv system. It gets fed back into the intake tube and the idle control motor gets high velocity flow of air with the oil particulates in it. The particulates bakes to the IAC due to the heat of the throttle body and intake temperature.

The EGR feeds into the lower intake and no exhaust gases pass through the IAC.

The carbon build up on EGR valves is common and can build up quicker with the use of poor quality gasolines.

Regular removal and cleaning will extend the life of the valves. If left unattended, the carbon build up on either causes restriction when the motor tries to open the valves, leading to failure. You can use a throttle body or carburetor cleaner to dissolve it. If its really heavy, let the pintle side of the valves soak in Sea Foam for a while, then use a soft bristle brush to clean the soot off.
 
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