Car use to idle at 750 RPM now dropping down to 500 and almost stalling

rumbles?, did the RPM drop below 800 RPM? that is called idle failure
and when it does, idle can go to 400 rpm and will shake hard.
and is normal for illegal idle speeds. so post that first.
post that engine stalls
and that the RPM is 400-500 just before the stall.
then post if the fast right foot can save the stall (a key test !!!!)
if easy the ISC is sticking.
if tad hard the EGR is stuck open'
if impossible to save. then more possible (many)
ever do the 60k mile tune up this decade????,. if not why not./ now.

check the MAP sensor (manifold absolute pressure). The ECM (car computer) uses that to keep idle at minimum 750 RPM. It's normal for it to run high when cold. These small 4 banger motors typically run hot, and they won't run right IF they're NOT running hot, ergo the idle is usually high when it is cold so as to cause it to warm up quicker. If the RPM's drop below 750, suspect the MAP sensor, &/or ECM.

almost sounds like the cruise control is engaging

need to clean the screen on the IAC valve.

Check the automatic idle module and the valve it controls. Look for a vacuum leak too.

Check for vacuum hose leaks or component clogs. You can use vacuum pressure tester.
or turn the idle screw down.

HAVE IDLE SPEED CHECKED AND ADJUSTED.IT SUPPOSE TO BE 750 TO 775 RPMS.

If you go to advance auto they will scan the car for free. if you write the codes down and update your question it will be easier to eliminate some of the sensors.

got same prob help us !!!