HI I recently changed my egr valve on my 97 bonneville se...the code was p1406...egr malfunction...was running great for over two months...and just tonight the check engine light came on with the same symptoms[stumbling...rotten egg smell...] i changed the gasket...and the tube looks clear...i guess this code has to do with the egr valve not responding to the pcm input as it should...its a gm valve from gm parts direct,,,also the correcxt vin # when i ordered it...any ideas? also did a recent tuneup including plugs wires fuel filter air filter...this does seem to occur when the car is started when warm...ie....was just running within a half hour before re-starting....

Check for the following,
Excessive deposits on the EGR valve pintle or seat. Remove the EGR valve and check for deposits that may interfere with the EGR valve pintle extending completely or cause the pintle to stick.
Poor connections at PCM or EGR valve. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
Damaged harness. Inspect the wiring harness for damage. If the wiring appears to be OK, connect multi meter and check circuit continuity while moving connectors and wiring harnesses related to the EGR valve. A change in the meters display will indicate the location of the malfunction.

Checked the connections and the wiring harness today...also tried unplugging the egr valve....the idle immediately smoothed out...im thinking this might be a computer problem...either a software update or a new computer..