hello i have a chevy 5.7 truck and recently the truck was running very sluggishly, idleing around 500 rpm, when i used the AC the truck ran SUPER slow, and other problems like that. so i took it in and the people apparently removed some hoses and cleaned out parts of the engine and so on. i got it back and i started it and it reved up to 1700 rpm and slooowly went down to sit at around 1200 rpm. and the service engine soon light was on. so i of course went back inside and they told me that it was "correct" that it was idling that high and that over time "one week" it would get better. IT HASNT! the truck is 4x harder to stop. it gets WORSE gas mileage, is there ANYTHING i can do to fix this?! thank you  

Generally a high idle is caused by either a sizable vacuum leak or a bad IAC (Idle Air Control) valve. I think your problem here is a sizable vacuum leak somewhere. More than IAC can correct for. This would also effect MPG and response at lower RPM because mixture would be off too. You might check ECT (engine coolant temp) sensor as it can sometimes effect idle if ECM thinks engine is still cold and could also cause a over rich condition and poor MPG. One more thing, if you are getting a SES light on dash you need to pull codes and see what it says. Places like Advance Auto Parts will pull and read them for free.  

what is a vaccum leak and where is it located on the truck and what do i tell the shop where im taking it to get it fixed?  

troyholland08:
what is a vaccum leak and where is it located on the truck and what do i tell the shop where im taking it to get it fixed?

A "vacuum leak" is when atmospheric pressure leaks into engine intake by means then throttle butterfly, PCV and IAC. It could be in a lot of places but give idle problem it is likely to be a big one is it exists. Look at bigger hoses and fittings connected to intake and throttle valve body. Might check/change PVC valve if it has not all ready been down too. I would do a complete OBD2 scan too to see if it reports any issues.  

I would say #1 just take it to a shop, it would take us too long to tutor you vortec 101 #2 if the shop you are takin it to has no idea what a vacum leak is, take it a to a shop that knows what they are doing. #3 a shop should tell you what is wrong with the system and not have to ask you to seek for internet advice. Fuel injection is a tepermental system and will have a tendency to damage components down the line (cat converter, o2 sensors etc) It does not take weeks to re calibrate itself, at the most 20 minutes of driving.
In all honesty online troble shooting will take you days and will not work as good as having a scanner on hand and people that know the system.  

I know you probably don't want to hear this but the very best thing to do (in order to save money in the long run) is to take it to your local chevy dealer. That way the work and parts are warranted!!! You are gonna spend just as much money paying someone to spend twice as much time getting the same result. I would make damn sure that whoever I took it to warranted and backed up their work and had references to prove it. I have been down this road before and believe me you are better off taking it to the dealer. I have the same model truck and a problem like this can be a number of things.... good luck bro!!