I ment idle rpms in park and in drive.

I will check on the RPM at idle and in drive and post later today. Concerning your code, P0301, you have tried just about everything and many things twice. I was thinking about a 1989 LeSabre with 3800 that I owned many years ago. A miss developed on one of the cylinders and I replaced the injector with no change. My thoughts were that it had a bad injector driver in the PCM. When I replaced the PCM all was well! I am not suggesting this is your problem as your issue is intermittent where mine was constant. This does make me wonder if an injector driver in the PCM could have an intermittent issue? If so that could be a possibility.

I'm picking up what your laying down as a friend of mine use to say. Got to work on the wifes ford van probably the next few days but I will see if I can run that down it sound like a possibility I haven't consider fully let me get done with the van it got a coolant leak I got to find then I'll give you a update on what I find thank you for the suggestion

I checked my RPM in drive at idle with a result of approximately 650. There was variation of course. The range was from 625 to 660 RPM. If you need other comparisons I will be glad to supply info subject to the limits of my Actron CP 9580A.

Thank you sir

Well i got the van fixed today and got back to the buick. I went old school put a stethoscope on the injector it is tapping very steady like clock work even though the car was missing I listened to all the injectors they all sound the same. Even though I want to pull out o scope and watch amp draw and voltage on #1 while triggering off something else I've got a 8 channel hantek now so I should be able to do that one day when time permits but I would say the drivers are good just listing to it and since I have swapped the injectors around twice I would say it cant be the injector itself.

Thanks for your message and additional info. Using the stethoscope was a good idea to compare the sound of all injectors. The mystery continues even as more and more tests are made, components are swapped, and so forth. I will continue to brainstorm ideas as there has to be a reason that this is happening. Hopefully other members of this group will continue to offer support as they may have additional thought on this issue. I would like to think that we can find the solution.

Thank you for your support I do appreciate any suggestions

At idle the vacuum wonders between 18 to 19 with with the misfire being very active today at idle raising the rpms slightly I would guess around 1000 too 1100 rpms vacuum goes up too around 20 to 21. Fuel long term fuel trim at idle is about -3 short term near 0 when vacuum gauge is connected to fuel pressure regulator and regulator has no vacuum applied long term fuel trim goes to around -5. I believe because of the added fuel pressure. Just thought someone might be interested to know I think this would be normal.

I ment to say with vacuum gauge hooked to fuel pressure regulator vacuum line and no vacuum on the regulator the long fuel trim goes to -5 which I would think would be normal since there is a fuel pressure increase with the vacuum off the regulator