I have a d16z6. Every morning or after a few hours of sitting I go to start my car when it cools down or is cold and it idles up and down. Ive replaced the IACV twice, bled the coolant a TON, and cleaned the FITV. I can't figure it out, I have a cel code but I can't figure out what it is because when I try to jump the ecu plug nothing happens. I have honestly no clue what it could be. After its warm its fine though. I checked for vacuum leaks and I didn't find any. What could it be!

 

Thats strange. My car ocassionaly has a hiccup where the RPMs drop for a second right when it starts up. but only drops one time and after that its perfect. are you getting air everytime you bleed your coolant? and are you sure u are jumping the correct plug. what year? most of them its a blue 2 wire connector with a brown and a black wire. make sure you make a good connection when u jump it and turn the key all the way before it starts. i think u gotta wait about 10 seconds before assuming no codes are blinking. does your check engine light stay on? otherwise it might not be storing the code

 

If i start it and while its idling up and down, if I squeeze the lower radiator hose it starts going away, like theres no pressure build up in the system which is making it do it. I don't know what could be causing that though. And the CEL is always on when im driving and I jumped the correct one its a 95 and its blue, and nothing happens.

 

I have a 98 EX with the Y8 motor and had a weird problem like you describe - it would stutter when i started it up cold. I wound up pulling the injectors, and cleaning them off with spray cleaner and dumped 1 liter of Seafoam treatment in a tank of fuel. Ran that through the tank, refilled and changed the fuel filter.

I got another liter of Seafoam and poured a third of it in a small cup. With the engine cold, started the engine and pulled the vacuum line from the fuel pressure regulator and used that to suck the Seafoam into the intake. I did not stick the tube right in the liquid, but let it 'slurp' the liquid up while my son held the throttle at 2000 RPM. This took about 45 - 60 seconds, and when white smoke started to billow from the exhaust, I shut it off for 5 minutes (per instructions).

After 5 minutes, I restarted the car a TON of white smoke just poured from the exhaust. I drove the car for about 5 minutes and it made one heck of a smoke screen! After about 5 minutes the smoke died down and the car was running smooth...

I did this on Friday afternoon and have been running the car for the past 4 days with no stuttering starts - and the engine is running REALLY smooth.

To add - my fuel mileage jumped from 30 - 31 mpg to between 34 - 35 mpg...

 

check your radiator before you start the car. low coolant levels in come cars cause the camshaft position sensor to misread, dont know if civics do it but legends will have idle problems with low coolant level. when the car warms up the coolant goes under pressure and expands. so if you bleed your car do you still get air coming out or before you start it check radiator level

 

The coolant is never really low and there's no air in it either. I'm thinking maybe a map sensor