Possible it has vacuum leaks, have you checked over the hoses at a minimum.

 

I have good vacuum to the solenoid and the vacuum system checks out.

 

If you have replaced The EGR Solenoid and the Valve and it's still not working properly this may be an Issue with the EGR valve module. It would have sampling metal tubes coming off the exhaust manifold and link to the EGR valve and to the Sampling meter. This Module communicates back to the ECM on the Status of the Amount of Exhaust gases entering the Intake. Basically, it's like a MASS sensor for the EGR system. If this monitor is dirty or the tubes are clogged it will not give and adequate reading to the ECM thus the ECM displaying the P0400 Code. Clean the harness and check for a leak in the lines connecting to the module. If the module working perfectly fine, it would be a Vacuum related issue, or you may have a faulty ECM.

 

I'll look into this. I did remove the flex tube from the exhaust to the manifold near the EGR valve to check for clogs. Remarkable none of the passages appear to be clogged. If you manually actuate the EGR valve at idle, the car wants to die. According to what I've read, that means the passages are clear. I even used a snake camera to go inside the port of the EGR valve and it looks fine. I will try and locate the module as most likely I overlooked that.

 

From what I am thinking the way the ECM tests the EGR is when it is idiling it opens the EGR and looks for a rpm drop. If it don't see the drop it turns on the light. If the throttle is open just a little and the ECM thinks its closed... So I'm thinking if you had a bad TPS it could be a problem. Just a guess.. I think you can get a TPS reading of the CCM .

 

Just spitballing:

At least old school CCC carbs you could backprobe the TPS with KOIO to check for smooth increased volts through rotation.

I take it you've done the 'spray Gumout over the top front back sides while running' to check for intake / vacuum leaks.

Are you getting any other of the common collected list of 'off-idle stumble' symptoms that reinforce your EGR ails, or other components?

 

Just spitballing:

At least old school CCC carbs you could backprobe the TPS with KOIO to check for smooth increased volts through rotation.

I take it you've done the 'spray Gumout over the top front back sides while running' to check for intake / vacuum leaks.

Are you getting any other of the common collected list of 'off-idle stumble' symptoms that reinforce your EGR ails, or other components?

No other codes. Car runs fine except for that which will cause a sputter because the valve isn't opening. I've repaired or replaced every component including both cats and all 4 oxygen sensors. Weird thing is if I baby it, the code might not show up. Yesterday I was in a parade rolling at a 2MPH pace for over an hour and it never set a code. I could take it today and hammer the accelerator from a stop and guarantee it would come back on.

 

Just wanted to note that I also replaced the MAP and coil back when I had misfires and other issues that turned out to be fuel related (PO had the pump replaced and someone didn't fully complete the job by leaving a clamp off) but that was fixed and those issues went away. I'm looking into some of the modules like IAC, IAT and TPS as recommended. I am also going to look at the MAF as well.

 

Just FYI, there is a TSB IIRC allowing the pump to be disabled as it was determined to be useless. My 9c1 LT-1 was a federal car in its first life and they had removed the pump entirely. I was in FL.in those days so no smog checks.

 

Be careful, IIRC 95 is OBD 1 and 96 is OBD 2. They are not interchangable.

I don't think.you need to program it out, just disconnect it. Someone with a 96 LT-1 may confirm or deny that. Pull up the TSB and check.it. We used to have a grear ImpalaSS forum years ago which included all B & D bodied cars but I have been away from it for years now and don't recall details I used to.know😊😊

 

Yeah I know. However the computer will work, it just won't have all of the stuff OBDII has. The 95 one was pulled from a running Fleetwood Brougham and i still have the engine, transmission and complete wiring harness. The guy who programs on these said with the 95, he could turn off a lot of stuff and really wake the car up but the 96 computers are flakey at best. If I didn't need to pass emissions, I would have swapped it out already.