Engine shakes and spark plugs 2 and 4 are running rich

[johnny426]

I have a 93 240sx with stock engine (KA24DE).

Recently, the engine shakes pretty bad at idle (around 600), and the idle will drop if I turn on the AC, instead of going to 1000. Also, when I start running it in 1st gear, it seems like not having enough gas because it appear to be choking until it reaches around 3000 rpm. After 3000 rpm, it runs fine. This problem began after I changed spark plugs made by split-fire, the O2 sensor and removed Apexi Multichecker two months ago

I did a compression test and here is the readings:
#1 160
#2 150
#3 155
#4 165

I also looked at the spark plugs and they display:
#1 yellow/brown
#2 flat black
#3 yellow/brown
#4 flat black

These spark plugs were 2 days old and they are NGK stock type. I threw the one made by split-fire away.

Does it mean that cylinders #2 and #4 are running too rich? If so, is it abnormal? Misfiring?

I examined the spark plug wires and distributor cap. They are fine.

I also checked the distributor timing, and they are right at 20.

Throttle body was cleaned today.

I need your help.

Thanks in advance,
Johnny

[kalieaire]

search for "power balance" test and do the outlined procedures outlined therein.

[johnny426]

OK. I did the power balance test.

When I unpluged the #2 and #4 spark wires one at a time, I see no difficulty on the idle.

Also #2 and #4 are not sparking.

What do I do next?

[Warwick5s]

try new plugs?

wires?

cap/rotor?