No problem, I'm glad to help but want to make sure we are connecting at a reasonable level.
And to clarify a few points:
And to clarify a few points:
- The vacuum that opens the EGR valve comes from the throttle body. If you think of the throttle body as a vacuum cleaner then the EGR VSV valve is like someone sticking their hand over the end of the vacuum cleaner hose. When the EGR VSV is closed then negative vacuum/pressure builds up in the hose and when the EGR VSV is open air flows into the system and no relevant vacuum builds up. The throttle body vacuum has to pass through the EGR Vacuum Modulator which controls if/when vacuum will pass on to try to open the EGR Valve but when vacuum does pass through the modulator and hits the EGR Valve the EGR VSV has to be closed for the vacuum to be able to build up and open the EGR Valve.
- Hopefully you don't need a full redo of the vacuum lines, and maybe they are fine. If they are old or don't fit tightly then a redo is a good idea. If it all looks good and if the EGR VSV valve tests good in isolation then another option could be to put the vac system from EGR Valve to EGR VSV under low pressure (could be tricky to block off the circuit but you could clamp the vac hose near the EGR VSV and then introduce pressure at the EGR valve). While under pressure you could spray all of the connections/lines with soapy water to check for leaks while also listening for air escaping.
- If I had understood where you were starting from better I could have been more thorough in my initial responses and at this point we've covered more ground than is probably necessary in this thread, with the goal of helping you understand the system. Once you grasp what the system is doing and how it does it you should be able to more easily isolate and test different parts of the system and find/fix issues pretty easily. The goal is to run quick/easy tests first to find the problem and to skip harder work/tests unless you don't have an easier option. Isolating a problem causing a PO401 will typically take 5 or 10 minutes once you understand how the parts of the system work. There's nothing wrong with it taking longer, especially if learning is ongoing, just keep in mind that this should come together and be relatively easy at some point.
- Owning an 80 is way better when you can work on it yourself but it takes a lot of learning to achieve that. All of us that work on our 80s have had to learn how to do it and most of us have years invested in that education with learning ongoing. Even though the EGR system is non-essential you are learning a ton as you work through troubleshooting and fixing the system and most of those skills will be relevant beyond the EGR system. The knowledge you are gaining is priceless if/when you encounter issues while operating your 80 and the satisfaction of fixing things yourself is huge so your efforts will pay off. Once you kill this PO401 you'll get satisfaction every time you drive the 80 without that check engine light staring you in the face
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