I have an Infiniti I30T I live in MA. with 255,000 miles Problem 1 - The 1st start in morning the car will start but sometimes it will want to almost stall. I think i it is like the RPM'S like drop, it can stall at times but you can prevent the stall if you hit the gas pedal. Once it does get past this initial sarting issue the car will idle fine, somewheres around 7500 in general runs great. This starting issue is my first problem. Do u think taking off throtle body and intake air control valve to clean might help?
Problem 2 - I do have CEL with a knock sensor (KS) code and small eval leak had these couple years. New code misfire cylinder 3, just came up too car was sputerring. Changed coil 3 with used oem coil ran much better, sputtering misfire gone, reset CEL. Then jumped on car CEL flashed for 3 seconds then immediately stopped flashing but went back on, not flashing now but light back on same codes with misfire 3 again. Should i change plug now in cylinder (3) or consider doing all plugs? Car still running fine.
I replaced the knock sensor with non oem KS, code did not go away, then replaced with a used oem KS. Light still on, when colder temp outside light goes away. KS and evap leak code been problem for years. Where should i start repair i think would be cylinder 3 misfire even though car is running fine, i did use used oem coil i do have other used ones except ocassional starting issue then plugs? I really think taking off throttle body for cleaning could help, especially the ocassional rough start where it wanrs to initially start. Please help car runs great and i want to keep it another 100,000 miles. I change oil religiously little help please, forum knows all!

 

The knock sensor code is rarely the knock sensor itself. It is a warning that the engine is not running correctly. And you know that the engine is not running correctly because you have the P0303 code. Plus, the knock sensor code DOES NOT turn on the check engine light. The other code(s) do that. When you fix the other problem(s), the knock sensor code will go away.

When you have a cylinder misfiring and the check engine light is flashing, the flashing means that the misfiring is happening right at that moment. When the light is solid, it means that you had a misfire but it is not happening now.

Possibly you replaced a bad coil with a not quite as bad coil. Swap the coil on cylinder 3 with the coil on either cylinder 1 or cylinder 5 and see if the changes to the other cylinder. If it does, the used coil was bad. If the problem stays with cylinder 3, then maybe the fuel injector is bad.

I rather doubt that it is the spark plug, unless they are the original plugs that have never been changed.

 

Dennismik thanks for response and all makes sense what u said. I do think the evap leak could be a very small exhaust leak. What are your thoughts with the initial 1st morning start, ocassionally it wants to stall or its like rpms drop but feather gas csn prevent yhe stall. Do you suggest removing throttle body and gasket and cleaning it with TB cleaner? When its cold outside problem more frequent but usually just the initial morning start.

 

The evap leak is not exhaust related. What is the exact code you are getting?

The morning start problem can be a lot of things. I think the 2 most likely are the throttle body needs cleaning or the ECTS (Engine Coolant Temperature Sensor) is bad. I don't think that you have to remove the throttle body to clean it. I don't remember taking mine off, but it was a few years back.

The ECTS can be checked while you sit in the front seat of your car without removing anything. The catch is that you have to have an OBD code reader that displays live data. Coolant temperature is one of those pieces of data. In the morning when the engine is cold, you plug in the OBD reader, turn the ignition on without starting the engine and read what the engine coolant temperature is. If the temperature reads a lot higher than the air temperature, the ECTS is bad. This causes the ECU to send less gas to the cylinders than what is needed for a cold engine.

How many miles do you have on the current spark plugs?

 

An other possibility is the issue I had this past winter:

When the car is cold it starts instantly and also instantly dies unless I touch the gas a bit before it dies.
Once I've 'caught it' it seems to do a normal 'cold idle' of around 1000 rpm until I put it into drive. Then for the first 2-3 minutes of driving when I come to a stop it idles initially around 400 rpm, then slowly over about 5 seconds rising to 700 rpm. After the first 2-3 minutes of driving it idles normally at 700 rpm at all times when I stop, and if was to turn off the car and start it again it would run properly.

So in a nutshell, stalls instantly and has low idle when cold.
Starts and idles normally once the car has been driven a few minutes.

What it ended up being was:

The issue was the fast idle plunger which moves in and out depending on coolant temperature, apparently this actually functions using a wax pellet within the part which eventually can wear out. Once replaced the idle speed is rock solid after start with no drop at all. Expensive part though, ~$200 USD.