How can you tell if your mass air flow sensor is bad?

Question

I have a 1998 Mercury sable LS. recently ( a couple months) i have noticed that when i start my car, it idles at about 1500 rpm. After i drive it a while it idles at about 1000rpm, when it is in park. When i put it in drive it goes down to about 700. I thought it could be one of the 4-vaccuum leaks, MAF sensor, fuel injection, gas pressure high or low. I have ruled out vacuum leaks and fuel injection, so i think it is either the pressure valve or MAF sensor. Thank you!

I have also noticed that it has a problem shifting gears sometimes, the rpm will go up to about 4-5000 rpm before it catches and starts accelerating, which jerks my car because it catches at such a high RPM. Any help would be appreciated!

Answer 1

start your car and tap the mass air flow sensor, if it stumbles or dies, its bad.

Answer 2

well if you have the A/C on the car would rev a lil higher than without it on but 1500 idle is quite high. is your check engine light on? also I would consider the throttle position sensor, and check the wires to it and the MAF sensor, as for the shifting problems it sounds like your tranny might be low on fluid or need the filter and fluid changed or perhaps someone has gone from reverse to drive without coming to a stop first a few times, this will grenade a tranny. sounds like one of the bands in the trans is slipping. when you shift from park to reverse or drive is the shift quick or would it sit there until you rev up the engine? any more info you could provide could be useful.

hope this helps