Fixed Vibration (see details)...Still Hesitating...UPDATE...Fixed!

[AFARR]

Pulled the Front Subframe. Welded the engine mount area on the passenger side (Cracked, and bent downward). Didn't trust my weld, so I also took a 1/8" x 2 1/2" piece of sheet metal. Cut roughly a 6" section. Drilled holes to match the Front subframe front bolt hole and then ran it back across the engine mount and drilled the hole to match the engine mount (and tab). Used 2 bolts to form it into the proper curve. I also put a 1/8" thick washer on at the front (rear bolt) subframe bolt hole (to keep it level).

Had a rough time with the engine mount on that side--top part sheared off while I was trying to remove it. Had to grab the remaining little bit with a visegrip and turn it slowly (have some NICE bruises on my elbow to show for it from the times it slipped and I hit the front bumper/spoiler).

I used early 318 (Solid rubber. $11 apiece) engine mounts--they work fine. A bit more vibration is transmitted, but since it isn't as bad as when it was cracked, I'm happy. No longer has the rough vibration on turning right/accelerating.


Still have some hesitation:

Signs/Symptoms:
Happened after I pulled the intake manifolds (and replaced the gaskets) and removed the throttle body heater plates--in the process of eliminating the leak from the plastic tube that connects the block to the heater. I also checked the spark plugs at the same time.
To do this I disturbed the fuel rail, intake manifolds, plug wires, and AFM.

Rough idle (at 800rpms)...just feels rougher. No significant change in idle RPM (doesn't drop). If I hold the gas pedal slightly in (bump to 1200 rpm, it seems to smooth out.

Hesitates (seems to occur between 2000 and 3500rpm UNDER LOAD. Don't seem to get the hesitation while out of gear and giving it gas.

Once you reach cruising speed...65-70, it seems to be fairly smooth, however, if you drop the gear to go up a hill, etc, you notice it again.

Warm/Cold doesn't seem to matter too much.

I do hear what sounds like very, very mild pops (backfires).

As was pointed out before, backfires are usually unburned fuel.

Now:
I checked for vacuum leaks (none noticeable), and I had replaced the bulk of the hoses under the intake. Used new gaskets for the intake manifolds. ****I would have assumed that a vac leak could cause lean running and a drop in idle RPM, not the backfires, etc.***

I checked all 4 coils. All read 7-8 ohms (all 4 read the same). Plugs look fine (new Bosch +2---Yes, I know, but they are direct replacements for the ones that made 40k miles with no problems.). Plug wires all read 6k ohms, even with moving the wires. They appear to be thicker than original, and are blue in color--I would guess that a Previous owner replaced them, but not sure of the miles.

My thoughts...however, I'm not sure how to check them:
Disturbed the fuel rail, and maybe at least one injector has gunk and is spraying a stream (leaving unburned fuel), rather than a spray. I did get a recommendation from Roadfly to use a mechanics stethoscope (which I have) and listen for the various clicks from the injectors working.  That wouldn't guarantee one wasn't spraying a stream rather than a spray, but might show if one is stuck open.

Disturbed fuel rail...maybe I did something to the Fuel Pressure Regulator.

Maybe the plug wires are bad? Coils also?

Finally--I did pull the AFM & filter box (and clean the LOWER box--not the upper part with the AFM attached). Maybe it is reading wrong? How is the best way to check?

Any other thoughts?

Thanks!!

[AFARR]

Looks like I found the source of the hesitation.

Bad coil. Tested fine on Ohm meter (0.8 ohms--same as the others when cold)--but must be intermittent with vibration and/or heat.

Replaced Coil #4 with used coil and it idles and it runs normally.

I had tested the plug/wires with a noid light...seemed to work well on Cyl 1-3 but on 4 was intermittent.  Due to the length of the boot for the plugs, it was hard to get down on the top of the plugs, but that was the presumed error.  That helped to narrow it down to coil or wire #4 (new plugs had been installed already).

Plug wires are in good shape (work fine with replacement coil). The guy that sold me the coil had the wires from his E36 and I tried a replacement wire (for the presumed #4 bad wire)--seemed to work a bit better when cold, but once it warmed up, it was still hesitating.

Replaced the coil and used the original wire and it is doing well.

Will drive around town for a while to test before making long journeys.

Thanks for the help!