have a 2000 Trans Am. I've thrown the p0405 code a couple of times for low-voltage on the EGR valve. It seems to happen when I do a hard acceleration. Most often if I'm on the freeway doing 70 and then I punch it and kick it up to 90 I'm just take my foot off accelerator it starts coughing and choking and throws the code. I took it to a shop they seem to think it's something in the wiring harness but they haven't been able to find it. I think it might be something to do with a weak or bad motor mount that causes the motor to twist and pulling wiring somewhere does anybody have any thoughts

 

Do you have smog inspection? If not, disable and remove the EGR system. It is not needed for the engine to properly function.

 

california car, I do currently have smog but by next year will need to have new inspection.

 

Oh OK. Check all related grounds, and any frayed/chewed up wires.
I feel your pain, also a Cali resident.

 

Disconnect EGR and test to confirm no issue. Trace wires from EGR to PCM to confirm no issues. You could do a wiggle test while monitoring the EGR supply signals at the EGR and position sense signal at the PCM and look for erratic signal. If all good, replace EGR.