1995 3.8L runing rough, stalling, shuttering

friend has a 1995 oldsmobile sihloutte 3.8L we got as a project to get running right, as 2 problems left.
1. When going down the road at any speed of 30+ MPH the car shutters whenever you let off the gas and it gets to 1500 RPMs, press gas and it goes away but comes back at 1500 again, it also shifts hard ever gear. we are planing on flushing the tranny and changing filter hoping that works, i think its something in the toruqe converter, but if you know anything it could be please suggest it...

2. When the car is idling at first it idles loppy between 500 and 1500 rpms, when you drive it and come up to a light, it idles really low (500+/-) and usually stalls, you start it and it starts right back up. its getting bad any ideas please help.

here is all we have done so far:
-changed plugs
-changed fuel filter
-changed PCV
-New ECU
-new ignition switch
-new exhaust

Ideas that could be bad:
-plug wires(look new)
-TPS
-CPS
-EGR valve
-O2 sensor
-fuel pressure regulator
-change tranny fluid

before i go to the local U-pull-it yard and get ever sensor I can find please let me know if you have any ideas...

As for the car shuttering, check the torque convertor solenoid. It appears not to be locking and unlocking the torque convertor properly. Don't flush the transmission as you are just asking for additional problems. Change the fluid and filter but don't flush. You may want to change the vacuum modulator located on top of the transmission. This is a simple fix for a few dollars and may cure a lot of your shifting problems.

As for the idle problem, clean or replace the IAC motor. If the car is hunting for idle then it usually points to a malfunctioning IAC. You may be able to clean it rather than replacing it.

Please read out the faulty codes with a OBD1 interface and software. This will help you a lot!

By all means try to get the codes: in ,95 there were obd1 as well as obd2. IF OBD1, the diagnostic polug will look like this:
www.avigex.ca/xport/plug.jpg
with connctors A,B, and M(under A). If different it is either second series OBD1 or OBD2..that require to be read with a scan tool .

If plug similar, then:
Jump together diagnostic plug connectors A and B with a small wire
TUrn key ON
CEL light will blink code 12 3 times (one ulse of light then 2 pulses, 3 times) then will start giving the codes, if any, like 23 will be 2 pulses, then 3 more..Once finished, it returns to code 12.
codes here:
www.avigex.ca/xport/3800codes.jpg

Pay attention to the EGR valve: it is a good candidate in most similar cases (codes 53,54,55,56): your problem looks as if one bank (this is a 3 port valve) stays opened. it is electrically operated, you cannot force it closed....

By all means try to get the codes: in ,95 there were obd1 as well as obd2. IF OBD1, the diagnostic polug will look like this:
www.avigex.ca/xport/plug.jpg
with connctors A,B, and M(under A). If different it is either second series OBD1 or OBD2..that require to be read with a scan tool .

If plug similar, then:
Jump together diagnostic plug connectors A and B with a small wire
TUrn key ON
CEL light will blink code 12 3 times (one ulse of light then 2 pulses, 3 times) then will start giving the codes, if any, like 23 will be 2 pulses, then 3 more..Once finished, it returns to code 12.
codes here:
www.avigex.ca/xport/3800codes.jpg

Pay attention to the EGR valve: it is a good candidate in most similar cases (codes 53,54,55,56): your problem looks as if one bank (this is a 3 port valve) stays opened. it is electrically operated, you cannot force it closed....

1995 model should have OBD1 second serie, or could have OBDII. In both cases, you will need a scan tool, or an interface and software to read the codes.

There is a different type of EGR valve for 1994 and 1995 model, 3.8 engine, compered to earlier years. This valve have only one port, but this port can open more or less, depending on engine running parameters. A sensor inside the EGR valve is keeping track of how much the port is opened. If there is bad electrical connection inside the sensor, You will get a engine running bad on low load and idling.