OK, so it sounds like the idle might affected by the temperature of the engine. Let me know if you think the problem is related to the temperature of the engine.
It could also be a vacuum leak or a problem with the Fuel management system.
With the engine running listen for air being sucked into areas around vacuum hoses, rubber intake hoses, etc. Move them around also as it might make the noise more apparent. I also use a string and drag it around the area where I hear the vacuum leak. I just did a timing belt on a car and cleaned the intake. It had a vacuum leak and I replaced a few vacuum lines that were suspect because they were hard and brittle as rubber hoses will do over time.
I was dragging the string near the throttle body where it meets the intake manifold. The string got pulled towards the place where the 2 meet. I pulled of the throttle body and I had put the gasket on wrong and a vacuum circuit was not sealed. I cleaned it up and put silicone on the gasket, which was high quality enough to reuse, and it sealed up and took care of the issue.
If it isn't, it sounds like a vacuum leak or the FIT, and maybe the IACV. The intake and throttle body could be dirty, as well as the Idle Air Control Valve, (IACV), and the Fast Idle Thermo, (FIT). If the Intake tract and throttle body are dirty, that can affect performance. If they are dirty, the IACV, (which controls the idle as the engine load increases from; power steering, air conditioner, headlights, other accessories, etc. The FIT control the idle in sort of the same way, but it works when the motor is cold like a choke and it can fail which can affect the idle even after the motor is warmed up.
There are also emissions stuff like Exhaust gas return, Positive Crankcase Pressure, PCV Valve, etc. Which can have some affect but not as much as the other items.
So, try the following to clean up the intake and fuel injectors. Remove the intake hose where it meets the throttle body and look in the throttle body with the butterfly open. Let me know how dirty it looks. Then get a can or two of BG44K and change the oil after using it. It works better than any injector cleaner that I have used and it works so well, the oil needs to be changed from all the deposits it removes. Also, if you can hold the throttle body butterfly open, get some carb cleaner and spray it down the intake with the motor running. Don't use a whole can or anything, just enough where you can tell everything got soaked from the cleaner.
To recap information of importance;
Do you think the problem is temperature related?
What do the spark plugs and air cleaner look like?
Were you able to find any vacuum leaks, (listen for them and use a string)?
How dirty does the intake look?
Also, this site has a lot of good diagnostic walk-throughs and links to BG44k distributors and repair shops near you.
I will watch this post for your reply and get back to you ASAP.
Tuesday, February 1st, 2011 AT 12:27 AM