Ok sometimes when I warm my car up its idling fine and then it start making a weird noise from the front and from the muffler, its like a pu pu pu, and when im driving slow it does it aswell it feel like the car wants to die, also when im at a light it idles normal and then idles fast and then goes back to normal, engine has 168k, I got a oil change a few months ago, I haven't changed my spark plugs in a year, um I haven't done any major repairs, just a cat 6 months ago, what can my problem be