I have a 2000 Isuzu Trooper that had a PO401 code that would reset and then 2 miles later the light was on again - I found if you remove the EGR valve and start the engine that the engine should idle rough - If it doesnt and you have vacumn at the intake port spray carb cleaner down the port slowly and see how long it takes for the engine to run rough - Keep spraying till the engine dies and spray some more down the passage and let the engine set for 5 minutes and then restart the engine - it will run rough at first but clear out - you should be able to feel the engine RPM change when you put your finger over the intake vaccumn port for the egr - If not then repeat the cleaning method again - If you do feel the rpm change then put the egr valve back on and clear the code and run your drive cycle to see if it is fixed.
I have a 2000 Isuzu Trooper that had a PO401 code that would reset and then 2 miles later the light was on again - I found if you remove the EGR valve and start the engine that the engine should idle rough - If it doesnt and you have vacumn at the intake port spray carb cleaner down the port slowly and see how long it takes for the engine to run rough - Keep spraying till the engine dies and spray some more down the passage and let the engine set for 5 minutes and then restart the engine - it will run rough at first but clear out - you should be able to feel the engine RPM change when you put your finger over the intake vaccumn port for the egr - If not then repeat the cleaning method again - If you do feel the rpm change then put the egr valve back on and clear the code and run your drive cycle to see if it is fixed.
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It may be a bad EGR valve or it may just have carbon buildup. It can also be carbon buildup in the intake. If your Trooper is hard to start, idles poorly, and runs rough the EGR valve is more than likely bad. If you are not experiencing these symptoms then it is probably just dirty.
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