J30 needs help

[jcdavoin]

I own a 95 J30 with 106Kmiles on it.I am posting here since the 300xz and J30 share the same engine.The car always starts good. Warms up good.Idle speed is good for a while (after car is warmed up).BUT, if I were to stop the car and let it sit for 15 min, the idle speed gets messed up like its missing cyl or something.The coolant circuit has been flushed, the temp sensor changed, air filter, Spark plugs are new.I even swap the MAF with a used one and still the same deal.I could drive the car for hours, as long as I am moving, it ildles good.Any ideas.

I appreciate the help.

[NY94J30]

I would have guessed MAF. You're better off posting in Infiniti general or Infiniti online mechanic.

[NISTECH]

I will assume you mean the car is sitting idleing for 15 mins straight?

If thats the case You may have a very small fuel leak from the injectors. A leak down test on the fuel system would be a good idea.

Also what type of plugs are you using? If they are not NGK I recommend you get those for your application as nissan/infiniti's dont like other plugs much.

[jcdavoin]

What I meant is I shut down the car completely for 15 min then it restart no pb but the idle gets bumpy (ok for 5s then it's like it's going to stall). I think something is getting affected by temp. I thought maybe the O2 sensor but don't know if they are used at idle???Regarding the Spark plugs, I just changed them from Denso to NGK per Infiniti spec for the J30.

Thanks for helping...

[NISTECH]

Do the fuel leak down test anyhow as temp will effect its oring seal. see if it is loosing fuel pressure when you cycle the key on a warmed up engine.