My Car soounds like its going to stall, its reving high and low, worse when air con is on, I recently took my car to hyundai dealer to have it looked at for this problem, they called me at work and said it may be the speed sensor however probably just the plugs and leads, so they replaced all plugs and leads for the cost of $639.50, I collected my car paid them but the problem was still there, I discussed it with them they advised a new sensor will be required, at $900.00 but they could get me a second hand one, (why they changed the plugs etc-beyond me) so I agreed to the sensor and explained I just want the noise to stop and the high random reving, they assured me all will be sorted,(pick up your car at 4pm but instead they kept it over night) anyway at that time I pointed out another noise that had developed which was the front brakes and they advised they would take a look and repair if nesacarry, upon finally collecting my car after this work was done and another cost of $689.00 later I started my car and it reved sooo high(worse than before) and in reverse was making the horror stalling noise again, i ran into office told the guy(manager) who just taken my money to which he replied "oh that noise is your exhaust" OMG is this a nightmare or what, I am a single working mother with no family here, what the heck is wrong with my car? and who can I trust to actually repair it? or does anyone know if this is a common problem? thankyou for reading my query