2.8L Missing/Shaking problems when warm

[mstrjon32]

I've got my 2.8L Regal Custom with 109K + ?? = ?? miles (broken odometer) and I'm having some problems.

 

I bought the car about a month ago, and when I got it, it was running pretty good, but I was getting some hesitation and the engine was missing when I was cruising on the highway at a constant speed (under acceleration it seemed to be fine). It also was kind of "bogging" down right after starting, and then recovering to a normal idle. Naturally, I figured a tune up was in order.

 

Not looking to spend a ton of money, I went out and bought some things for the tune up: A bottle of Lucas Fuel Injector cleaner, AC R44LTSE plugs, Autolite professional wires, a fuel filter, and a PCV valve (which I still haven't gotten around to installing).

 

I did the FI cleaner and the fuel filter right away, then just two days ago I got around to doing the plugs. The old plug wires were of various brands, but the same AC R44LTSE plugs came out. They all looked to be in pretty good shape, no unusual wear on them. After much swearing I finally got the wires off the rear plugs, and put the new ones in using anti-sieze, gapping them to .045, and torquing them to the factory spec of 24Nm (as listed in the factory service manual) then attaching the wires directly (in retrospect I should have pulled the boot back, attached the wire, then slid the boot back over---I'll probably be doing that tonight ). The only glitch I noticed when doing the job was there was a touch of corrosion on one of the contacts of the coil pack for cyl #4, I believe. I just connected the wire anyway, and when I ran the car it didn't seem to be missing or having other problems, so I shurgged it off.

 

The next morning, when I took the car to work, I had no problems getting to work, the car was running much smoother, it started and idled great when cold, and overall performance seemed to be much improved -- the constant speed hesitation was gone. I was very happy with the results. However, on my way home, I made a few stops and was driving for a longer time--giving it enough time for the engine to get hot. The car started to miss and shake consitantly with constant speed (something it only did occasionally before hand) and stalled three times on the way home. When I sit with the car in park, and hold the revs at ~2500 (no tach, so can't tell you exactly), it revs up to speed ok, but as I hold it there, it starts to sputter and miss, after 5 seconds, it is missing badly and shaking violently, however, when cold, no problem.

 

I'm going to check all the plugs, make sure the torque spec is OK, and clean off all the contacts on the coil packs tonight. I don't think its some kind of contact problem with the plugs--since it runs fine when cold. The only thing I changed since the problem began though is putting the new plugs and wires in, so nothing else has really changed, and I don't know what else to blame. I'm pretty much just looking for ideas on what could be causing this. I want to try and fix it ASAP, as I planned on taking the car on a 600 mile trip this weekend.

 

Thanks for your help in advance.