Thanks all for the ideas. Removed the serpentine belt and started it up this morning. Vibration was still there at the same RPM's as before. Maybe not as strong, but definitely present. Could be because it didn't get that cold here overnight. So we can rule out the PS pump as the cause, though there still may be something wrong with it due to the fluid and leak.
Will look into the firing order next just in case. It had a tune up right after I bought it - new plugs, wires, and I think maybe a new cap too. SO unless that guy hooked things up wrong, that shouldn't be an issue.
I looked down at the motor mounts today also. As far as I can tell, they look like they have some kind of cushion in them - couldn't tell if it was rubber or poly.
I've looked around at the vacuum lines before and haven't found any cracks or loose connections. Had to replace a couple because I broke them myself. They got replaced with brand new ones, same diameter, etc.
This vibration issue predates all of the above - it's been present ever since I got the car over two years ago. It's really the only nagging problem it's ever had, and multiple sensors/parts have been replaced out of an abundance of caution, and figuring they'd need it sooner or later. All of the vacuum solenoids, the EGR, the PCV, IAT, BAP, and O2 sensors have been replaced. And just did the fan and clutch. I've also cleaned out the MAF sensor, throttle body, and have a
K&N OEM style air filter in the stock air intake that I put in last year. The only EEC codes ever thrown out are the 44/94 for the crossover tube, but I've put off fixing that since it's not supposed to be a big deal.
I was getting really poor city mpg, and subpar freeway mpg until the O2 sensors got replaced this summer. PO had put in Bosch sensors, and I replaced them with new Motorcraft ones. Since then it's averaged a solid 16-18 mpg with average driving around, and I got 25 mpg when I took a 200 mile round trip on the freeway.
Engine was smoother after the new O2's, and then once I realized the fan was cracked and replaced that, it got really smooth. Except for that RPM vibration still coming through the steering column.
Question - since I know there's an issue with the crossover/smog tube, and that's the only error code I've ever gotten on the engine, plus the fact the vibration is worst when the engine is truly cold, could a blockage there or at the back of the intake manifold where it connects, cause that vibration when the air can't get through there the way it should? Since the solenoid valves close and bypass air straight to the exhaust once the engine is warm, and that's also when the vibration is nearly gone - could that be the answer?