2001 3.1 Bogging under partial throttle

[KnowClue]

First time poster. Fair knowledge about cars.

I have a 2001 Grand Prix with 3.1L engine with about 150K miles. Under partial throttle, there is a vacuum leak sound. The sound comes on and off while maintaining the partial throttle. When the sound is occurring, the engine bogs. When I push the floor it, it down shifts and stops bogging. No check engine light. I started replacing parts that seemed like it would help.
1. Intake Temp Sensor
2. MAF sensor
3. PVC valve
4. O2 sensor


At this point is when I started hearing the pulsing vacuum leak. I started blocking anything that has vacuum to see if I could get the sound to stop. When I unplugged the EGR valve, the pulsing vacuum leak sound stopped. I then replaced the EGR valve. Nothing changed. The pulsing vacuum leak sound still occurred under partial throttle. When the EGR valve wires are disconnected, the engine runs better and the check engine light came on.

I checked the EGR passage to the intake manifold and it is not clogged. I checked the EGR tube from the exhaust and it is not clogged. I am at a loss of what I can test / replace from here. One other side note, the coolant ran out before this problem started. It has always had some small loss of coolant since I bought the car 12 years ago.

Fixing the coolant issue I replaced:
1. Radiator
2. Thermastat
3. Temp sensor
4. Radiator hoses
5. Coolant level sensor

Any ideas on what to check now as far as the bogging issue?

Thank you much,
Jeff

 

[Fivefingerdeathpunch]

Have you smoke tested the intake for a leak?

I forget if the egr system has those metal tubes on the 3.1's.

 

[KnowClue]

Update. I drove the car more and it was bogging all the time. I then suspected the catalytic converter. I removed the O2 sensor and disconnected the egr tube from the egr valve . This opened up holes in the exhaust before the cat. The car drive some what better. I took it to the muffler shop and had the cat replaced. All good now.