[vicchang]

I cleaned the one on my 88 couple years ago since it failed NOx. The exhaust gas return tube (metal) was completely clogged by very hard black stuff (carbon deposit), as well as a rubber hose, and the EGR entry port on the intake manufold. I just dig the carbon deposit out, make sure all tube/hoses are clean and the valve moves freely.

I returned to have emission re-inspected, the computer can't measure any NOx and issue a warning that the exhaust gas is "diluted". The techs checked all my emission hoses and exhaust pipes making sure there is no leak or modification and retest. Same thing. He said I have a super low emission engine.