You need a EGR valve most likley. - If you post the fault numbers (DTC's) , you'll get more feedback.
Yea, when to TB/Plenum hasn't been takin care of (Cleaned) there can be repercussions. The EGR poppet valve is most likley hanging - Hence excessive
Flow = 402
Stuck Open Test
Whenever at idle, the PCM checks the voltage of the DPFE sensor and compares it with the voltage recorded by the PCM during the last Key On Engine Off state.
If the voltage is different this indicates a gas flow where none should exist, and the PCM stores the DTC P0402 EGR Flow Excessive
Gas Detected. This can cause confusion: in this context excessive flow means there is a flow where none should be detected, ie, the EGR poppet valve has stuck open.
Here's a better look at the valve. Note : The actuating rod is all called the poppet valve.
So - Your valve hanging enough to cause problems is my guess. This weakens the mixture sufficiently enough to cause misfiring, and manifests itself as a noticeable misfire/hesitation at speed and light throttle, not present when accelerating.
Last edited by jbrew; 09-23-2008 at 12:35 AM.