'97 EGR valve test for P0402

[Beargap]

My '97 XLT with OHV 4.0 V6 and 5-spd manual is idling roughly and throws a P0402 code. That suggests the EGR valve is not closing at idle, I think. Online searches suggest manually operating the valve to see if it is the valve or the vacuum solenoid. Any idea how to do that? Does the diaphragm come off the valve while installed somehow? Thanks for any help

 

[1998Exp]

The easiest way to manually control the EGR valve is with a hand vacuum pump. However, if all you need to verify is that it closes, simply disconnect the vacuum tube -- it should be fully closed when the vacuum port is open. If it still idles rough, the valve may not be able to close fully due to carbon deposits. In the old days I used to scrape carbon from the seat with a sharp tool while holding the pintle up by applying vacuum. If you are convinced that the valve is the problem, may make more sense to just replace it these days.

My '97 XLT with OHV 4.0 V6 and 5-spd manual is idling roughly and throws a P0402 code. That suggests the EGR valve is not closing at idle, I think. Online searches suggest manually operating the valve to see if it is the valve or the vacuum solenoid. Any idea how to do that? Does the diaphragm come off the valve while installed somehow? Thanks for any help

 

[Beargap]

The easiest way to manually control the EGR valve is with a hand vacuum pump. However, if all you need to verify is that it closes, simply disconnect the vacuum tube -- it should be fully closed when the vacuum port is open. If it still idles rough, the valve may not be able to close fully due to carbon deposits. In the old days I used to scrape carbon from the seat with a sharp tool while holding the pintle up by applying vacuum. If you are convinced that the valve is the problem, may make more sense to just replace it these days.

Thanks! The vacuum tube was a bit stuck, but no change in idle when pulled, so that is a good indication that valve is shot...it certainly looks pretty rough from the outside. I've ordered a new one and then will see if I can get this thing off, that might be a challenge. This truck has over 300K miles on it!