EGR Valve - it happened to me just after I bought my used 1997 Celica. Could be plugged or could need a new one. If you need a new one, check with different Toyota dealers. Three in my area gave me three different prices - from $125 to $88. I chose the $88.
exhaust gas recirculation flow insuficient
Engine,Emission Control System,EGR (Exhaust Gas Recirculation Valve),Exhaust system,ECM (Engine Control Module),
Engine,Exhaust system,ECM (Engine Control Module),EGR (Exhaust Gas Recirculation) valve,E40D (Transmission),Ethanol,
Engine,Emission Control System,EGR (Exhaust Gas Recirculation Valve),Exhaust system,ECM (Engine Control Module),
The unburnt exhaust gases are recirculated back through the engine by way of the intake manifold. This helps reduce emissions.
Exhaust gas recirculation insufficient flow detected
Exhaust Gas Recirculation (ERG) recirculates a portion of an engine's exhaust as back to the engine cylinders. On a Renault scenic, the valve is located at the top center of the engine.
Exhaust gas recirculation valve fault
Trouble code P0401 means: Exhaust Gas Recirculation Malfunction
It is an EGR code Exhaust Gas Recirculation Circuit Malfunction (32)
Exhaust gas recirculation. The egr meters a small amount of exhaust gas back into the engine. This gas lowers the combustion temperature which lower the a mount of oxides of nitrogen in the exhaust.
Left hand rear corner of the engine, below the exhaust gas recirculation valve (EGR)