Odd, dead cylinder issue. Need help!

[stephenschallenger]

Hey everybody, I recently purchased a 1991 300zx tt that was running on 5 cylinders. Recognizing that it was probably a coil pack connection or ptu problem, I purchased the car. (Cylinder 1 is the problem). Eager to fix the problem and begin driving my new (to me) car, I replaced the coil pack, coil pack plug, fixed all ptu connections, replaced the ptu with a known good one, and checked for spark. Here is what I found: The cylinder 1 coil pack is new and functional, the spark plug is new and functional, the ptu is functional, the wiring to the ptu connections is functional, and the cylinder 1 coil plug is getting similar readings to the other coil pack plugs. Usually, my next step would be to check for compression, and/or the fuel injector, but here is the problem: When first firing up the car, it runs perfectly smooth, then, a couple seconds after, as the car drops in rpm's, the car runs rough, and cylinder 1 no longer fires. When checking the cylinder one electrical components when out of the car, there is good spark upon start up, and within a couple seconds, the spark slowly dies on that coil. Then, the car runs like crap. Wait until the car is cold again, and its starts up brilliantly, but then starts to idle like s*** again. It's quite odd. I should note that I live in Arizona, and that even in the heart of winter, it never really gets "cold". The days linger around 70 degrees Fahrenheit. I would also check the cas, but I heard that when they go bad the car straight wont start. Can I get some input? Thanks -Stephen W.

[DCaff300ZX]

Sounds to me that the "good" coil pack is in fact not functioning correctly...replace it and see what that does.