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Keep in mind that the operation of the EGR is cut off on a cold start by the thermal valve in the underside of the intake manifold. If that valve has failed in the open position that will allow the EGR to work when the engine is too cold to accomodate the exhaust gas and choke your engine.


I am not familiar with the "Thermal Valve" on the underside of the manifold. Perhaps it is called something else? Where is it positioned and what does it look like?

I have gone over every inch of the air intake/vacuum hose system with starting fluid and also an unlighted propane torch (more control than starting fluid spray). I have not found anywhere that appears to respond and indicate a leak.

At the U-Pull-It yard I noticed some sort of valve with vacuum hoses attatched on the tire side of the manifold. It was right next to the single wire temperature sending unit for the temp guage. What does this little unit do? It had two vacuum hoses going to it ( I assume one in and one out). Since it screws into the coolant flow in the manifold, I assume it is a temperature controlled vaccum valve. Is this correct? Could this little unit have something to do with the problem?

You wouldn?t worry what people thought about you if you realized how little they did!
1988 Isuzu Trooper Limited, Bone Stock, 2.6L, 5 speed manual trany.
2001 Isuzu Trooper Limited, Bone Stock, 3.5L, Automatic.