I've got an high idle on my car with tiny backfire. So, I went to check up my car. The first place told me that is the intake gasket that need to be changed. The second place told me that is the IAC module and spark plugs need to be changed. Who should I trust? Please help, thank you.

 

How long have you had this high idle? Actually, what do you mean by high idle? What RPM? What are your mods? Any other details?

Offhand, I would say that they are both wrong.

 

My car is idling at around 1500rpm. No mods.

 

From my experience: My car had a high idle and back fires occasionally. (not loud back fires and only at idle, more muffled 'poofs') It was the intake manifold gasket.

 

with the engine running spray starting fluid around the intake manifold especially near all the gaskets. if the idle speed changes you have an intake leak. plugs will not make your car idle higher, maybe lower if they are really tired and misfiring.

 

I tried spraying carb cleaner around the gaskets when I was troubleshooting the car and there was no change in idle whatsoever. May work for everyone else but me, but just saying just because that doesn't work doesn't exactly rule out the gasket.