Back again, 93' bonneville ssei sc, 74,000mi code 56 seem to come on only when i release the gas pedal. but when i accelerate a code goes a way and never come back on as long as i keep my feet on the gas. I gave it a tune up , spark plug, wires, air filter
pcv, fuel filter. problem the same. but when i do accelerate, i notice a little delay and
stumbling which goes a way as soon as i hit 65mph or more. I replace the EGR valve
$213.00 and the problem the same. I have no problem shifting, a little slow on the boost
but it kick in. but two days ago, i started my car and it started idling rough then shut down i was able to start it back up and ran fine after. maybe two seperate problem. help.

I was recently plauged by a code 56. Thought for ther longest time it was the EGR. It is a Quad B driver fault (EGR/Boost control/Transaxle solenoid). Turned out to be the PWM solenoid in the tranny. My symptoms were exactly like yours, let off the gas, light comes on, accelerate, goes away. Took my trans mechanic 2 weeks to figure it out. I guess he was struggling with the same troubleshooting process, thinking it was EGR or boost control. If you do a search on code 56 in this forum, you will find a ton of info. I recently found out that you can easily bench test an EGR ( DRJAY). You can do this on or off the car. Might explain your idling issue. Most of the time a good EGR cleaning will help. I went through 4 at Advance to find one good one. This might help:

http://www.bonnevilleclub.com/forum/...ic.php?t=32746

Supercharge- before the other post I didn't know what a 56 meant. Was going to say a 93 with so few miles the car is saying DRIVE ME!!! Guess not though. Good luck with the fix

griff1455 that something to look at. also, i had cleaned my iac sensor which was
carbon, it has stop the rough idle for alittle while. but only when the car reach it operating temp. that ses lite would start to come on when releasing the gas pedal. could 02 sensor have any thing to do with it, or PCM or maybe a new IAC sensor.
something not opening or it voltage not right when i react operate temp. i will try other thing.