Hard to Start, Rough Progression to Fast-Idle; Runs Fine Otherwise
 

Does anyone else have stories about rough start-ups and erratic idling when below operating temperature? What was your fix? Here is my case:

When the car is cold (coolant temperature gauge reads at its lowest), the car takes 2-3 cranks to fire up (you can occasionally hear a cylinder fire up after you stop cranking) even after the fuel pump primes. And when it fires up, it starts from 400-600 and stumbles all the way to the cold-start rpm allowed by the air regulator. Whenever the car starts up when the engine is between cold and operating temperature, the car will fire up normally but idling will be rough (600-800).

Otherwise, when the car is warm or when the car is not idling, she drives like a charm :) If it helps to know, my car's biggest relevant mods are an NA2T swap, intercooler, PRW-2 ignition transistor, and PCV/EGR/FICD/AC delete/block-off.

Raw fuel smell and rough idle mostly when car is cold/below operating temp made me think my car was sputtering and leaving unburnt fuel. I know that I am not pig-rich as I get no black exhaust smoke or soot on spark plug electrodes). I am pretty sure that my MAF, CHTS, CAS, and O2 sensor are all good (either checked before or replaced in the past year with genuine Nissan part; I only weekend the car). My wideband O2 gauge (which has its own O2 sensor that is not input for the ECU) says that my idle A/F ratio is 22-26 (which I read is unusually and exceptionally lean) and 13-15 between moderate and full throttle.

Later, I will get fuel pressure numbers for post-prime and running conditions and check FPR vacuum to see if its fuel-related. I will also be checking electrical connections, spark plug electrode gaps, and ignition timing via timing light to see if ignition is to blame.

But in the meantime, please share with me any advice/stories.

I have the exact same problem on cold starts (first start of the day) every other start it fires up fine. I am thinking it's the CHTS. I have one on the way and will let you know of that fixes it. Also if you find a solution would you let me know please!

on a stock setup I would put the blame on the chts but since you don't have a stock setup could be other things.

cords probably not the chts. more likely fpr problem. but changing out the chts is not in the least harmful and fairly cheap. unlikely your and veggieeater problems are related.

If cords wants a better answer make a post of your own with relevant data.

the only time I have had weird start problems is when battery and battery cables were substandard. Z's electronics want full 12 volts to work. Weak battery, corroded cable terminations will give you fits. they are the heart of your electrical system Make them golden.

another possibility is all that useless junk hanging off the left side of the plenum to control the idle. I got rid of mine and blocked off the hole. I'm happier.

Assume both of you checked for vacuum leaks? Fuel pressure, ignition timing on spec. If you haven't checked those things and you want to solve the problem you need that data. Be nice to share with rest of us if you want some good answers.

second thought don't discount the bad starter hypotheses. My 83 was having problems and had to whack the starter once to get it to move. Lots of cranking to get her moving. New starter if you looked at the key wrong it would fire up.
Another lesson learned don't trust a new battery. 83 had gremlins spent much time and cussing tracking down stuff because I kept telling myself "new battery can't be the problem". when I finally broke down and got the battery load tested they gave me a new one under warranty and all my problems vanished.