I posted this in general engine and got no help - maybe it'll work here.

1991 GTA - has a tip in stumble and chuggle in low-rpm/high-gear, cruise BLMs of 108. I went through all the test on everything to no avail. Even the EGR tested well according to the service manual. On a hunch, I pulled the vacuum to the EGR and plugged the hose so there was no vacuum leak. All my problems were solved.

EGR duty cycle is going to 99% as soon as I touch the throttle. I think that is normal. But, since it's a negative backpressure design, I wonder if the vacuum bleed off isn't working well. The manual says to apply vacuum to the EGR valve and start the engine - the vacuum should drop and the valve should close. Well, it does, but not instantly. So, maybe the backpressure bleed-off diaphram isn't working well?

Or, maybe the exhaust gas is somehow too rich and the slightest EGR bogs the engine?

Any ideas before I pull the plenum and throw on a new EGR? BTW, I took out most of the EGR wall in the plenum and the exhaust is catless with a flowmaster.

 

Did your blms correct themselves when you pulled the vacuum for the EGR?

 

They went from really rich to just rich. This is a 180,000 mile motor with no blowby and perfect vacuum. I'm just trying to figure out if the EGR is leaking or not closing due to it's negative backpressure design, or if the motor is whipped and any EGR kills it. I'm leaning towards the former reasons.