92 400 engine miss till warms up

[aldedmon]

My 92400e's engine misses till it warms up.
Scenerio:
It cranks/starts first thing and runs fine.
let car run till idle settle and runs fine.
put car in gear and misses pretty noticably.
run car 10-20 min till get to operating temp and miss is no longer noticable.
Have done complete tune up before miss started.
replaced plugs again but miss seems to have gotten worse.
Have done the following FULL tune up replacements.
Rotors,Caps and Wires from FastLane
Plugs and O2 sensors
Everything EXCEPT the TBA which I understand may be bad as the car will occasionally "hiccup"/stutter a bit when cold.
Also car will puff smoke(fuel dump) like a 74 Caddy when I jump down on it and engage a passing gear.
Help!!

[400E]

Have you replaced the fuel pressure regulator? It's said to be a common source of rough idle. If you do, make sure you get the new and improved version from a dealership. It has a blue plastic piece at the bottom.

I'll be interested in other folks' thoughts as well since I too have a mild rough cold idle. (Replacing the fuel pressure regulator, rotors, and caps hasn't helped.)

[carman850]

Several days ago, I solved my 400E's cold rough idle problem by simply using some Pennzoil fuel system cleaner, the idle smoothed out the day after I added the cleaner, before I had invested $1000+ for the parts and many weekends for this annoying rough idle.

In my case, it seemed carbon deposit was the cause. My wild guess is that because of their extra high gear ratio (1:2.24), I seldom need to rev the engine to above 3000 rpm unless I want to drive aggressively, this might cause carbon build-up on intake valves and within combustion chamber.