If you are new to tuning nitro engines then my 1st suggestion is to not use the idle screw as a tuning option.
Second of all is to reset your mid needle to factory settings if you have adjusted it (if you have that info). Most motors are sold pretty close on the midrange settings, but the high end is fattened greatly to supply lubrication during the breakin process.
The high end needle is what you will want to focus on until you get more experience with tuning.
A digital thermometer (cheap = Duratrax for about $25) will greatly assist you on not only learning how to tune your engine, but making it last as well.
Things seem kind of backwards when tuning, colder days need more fuel because there is more oxygen in the air & hot days to the contrary. Seems like it should be the other way, adding fuel because it is hot, but That Is Not the case.
Anyway, make adjustments to your high end needle, & then run a lap or two to make sure that your carberator has been cleaned out from any previous adjustments. You are looking for top end speed at this point.
As far as idle goes, you should let the engine idol & then it should start to gain RPMs in about 20 seconds, that in my opinion is where I set my stuff up to. But this is just my preference.
Don't chase problems unless you have installed a quality glow plug.
Set your top end 1st, Idol next, & for now not the midrange (other than returning it to factory settings) & hopefully in about a month you will have learned enough that you no longer want to give up on Nitro (you will think that a few times) know abit more about tuning & truely realize that you made an excellent choice when you decided to go with NITRO.
My appologies for taking up space on this forum. Happy racing to you all.