whenever i cold-start my car, it idles fine around 1000RPM's for about 30 seconds. if i let it sit any longer than that, the RPM's drop to around 500. at that point, when i give it gas, it stutters quite a bit. once the car warms up, it runs fine.

i have also noticed that as soon as the RPM's drop to 500, it begins to emit a white-ish smoke exhaust.

this has been going on for a couple weeks now

newest mods: Brenspeed tune about 3 months ago
Zex nitrous kit for about a week or so

i have not thrown any codes so i have no clue where to start with the diagnosis.

 

500 rpm is too low, I think. It should probably idle at 750. How many miles on your car? Have you replaced fuel filter?

 

Go back to stock tune and baseline. If it vanishes, call your tuner with your results on his tune.

 

i wonder if coolant is getting
into the combustion chamber(s)

would a compression test help
in this instance

 

Mine idles at 850.

 

well, like i said, it normally idle's around 1000ish. actually a little lower.

the problem only comes when it sits and idles for more than about 30 seconds. then it suddenly drops to around 500.

i havent replaced the fuel filter in about 40,000 miles. the car just rolled over 70,000. i think i am gonna try that this week and see if it fixes it. i have been planning on it anyways cause it is about due.

muffler bearings??? explain please...

 

Muffler bearings is a joke.
Radio coolant is another.

You don't have a vacuum hose off like I did, do you? I took off my air intake hose and forgot to reconnect the vacuum line when I put it back on. The rpms would really take a dive and then shoot up and then dive and then shoot up. ...especially when coming to a stop.

 

Last time I had an issue like yours it was my MAF sensor had oil on it from an over oiled K&N on the '00. I used some contact cleaner and cleaned it and problem was gone.

Edit: and when it bogged; it felt like it was gonna die then jumped back up to 1200ish and fell normal... was very strange.

 

same here i had a problem like this and i cleaned my TB and maf and the problem went away

 

yeah, i kinda figured that...like blinker fluid huh?? haha.

i dont have any vacuum lines loose, i've checked those. i have not cleaned the MAF sensor in a while and have recharged the air filter a few times since the last cleaning. i'll try that too. still banking on the fuel filter though