My 2001 Crown Vic P71 SAP (with a little over 100k on her) is breaking up under a low RPM load. From a cold start it runs good then this problem gets gradually worse as the car reaches full temp, then heat soak. I'm pretty car savvy, this is not a trans shudder issue. The plugs are newer Motorcraft. I have a handful of spare COPs and have rotated them around. (with fresh dielectric grease) Weirdly this issue first showed up after I had my intake manifold off and then back on. (got a faulty replacement manifold and put my old one back on) then I had this stumble issue. After I put my new Ford Racing manifold on the stumble was gone, for about 700 miles. It seemed to show up gradually. I wondered if it was bumps in the road at first. Now, after a 25 minute drive, it's really bad. It will break up under wide open throttle too. Not getting any codes. I unplugged the DPFE sensor (EGR pressure sensor) and that didn't change anything (not sure if it would, I see lots of threads saying to replace that part) I'm kind of wondering if it could be something odd like an upstream O2 sensor or a fuel pressure sensor (I remember when I had my 03 Cobra, those would go and cause odd running issues). My little code scanner shows live data, TPS is consistent when it happens. I don't know enough about what to look for in other data to narrow the problem down further.