Engine light came on,dash light said "engine power is reduced" cruise control would no longer engage. had a real problem climbing hills,very sluggish. what is the cause?

Alarmingly, the speedometer needle steadily winds down from 75 mph toward 50. Just as you uncurl your feet and try to accelerate back to traffic speeds, the vehicle downshifts with a lurch and abruptly climbs back to over 80 mph. So you tap the brakes and disengage the cruise control to avoid a conversation with one of the many law enforcement officers lurking behind every other billboard. Toggling the Resume switch settles things down, holding to a legal speed on both the uphill and downhill sections of the interstate. The kids in the back seat have stopped threatening to throw up, too. Then you look in your mirror 20 miles later and see the lights. Red and blue flashing lights. You're doing over 85 mph and, odds are, Smokey isn't going to believe you have the cruise set to 70. Time to find out why your cruise control has a mind of its own.
IT'S NOT A BUG, IT'S A FEATURE
Does your cruise control fall out of engagement partway up steep hills? Actually, it will normally drop out if the engine has to work too hard, mainly because after a while there isn't enough vacuum left to pull in the servo after sustained near-wide-open-throttle. You'll just have to put your foot into it. Downshifting helps. Do you have to ride the brakes on longer downhills to keep from building up excess speed? That's normal too. The cruise control only has authority to reduce engine speed to idle. It doesn't activate the brakes. Modern cars, in an attempt to improve mileage, have very tall gear ratios, low-friction engine designs, low-rolling-resistance tires and optimized aerodynamics. That long downgrade outside of town may have accelerated your '60s-era Pontiac to only a couple of miles per hour above legal. But, it may well propel your new economy car to blatantly ******* velocities unless you intervene by braking or downshifting. Does the Cruise icon on the dash light up when you turn the switch on? Duh. Check the fuse. You may need to look in the owner's manual to see which one if it's not tagged on the fuse box cover. An aftermarket cruise may have an inline fuse holder in the wiring to the controller.
If there is power to the system, the next check is the brake lights. Brake lights? Yup, cruise controls have a switch to toggle them off when you touch the brake pedal, and many use the same switch as the brake lights. If one of the brake lights has failed, the cruise control thinks the brakes are on all the time and won't come on. Same result if the switch is incorrectly adjusted or broken or jammed. Wait, there's more--if your vehicle has a manual transmission, there's a similar switch on the clutch pedal. You may need to break out a test light or multimeter to verify the function of this array of switches. These switches usually are normally closed switches, and close their contacts when the pedal is depressed. We've seen several cases of intermittent cruise control dropout caused by a brake light switch that was adjusted very tight. Any small bump would jiggle the brake pedal down far enough to toggle the brake lights on for a brief instant--long enough to shut down the cruise. Adjusting the switch to specs (usually so the brake lights come on after the pedal travels 1/2 in.) fixed it.

A transmission issue would give vibration tremendously during uphill. If you're not getting the vibration, or burning smell of transmission fluid, suspect clogged catalytic converters.

Reduced power can be a multitude of things. Find out what code is present by using a scanner. The cruise control WILL NOT work if the check engine light is on. Once the check engine light is cleared, the cruise control will work again.

Try checking the small switch at the top of the brake pedal. There may be two one for brake lights and one for the cruise control. To ascertain what is what, pull one wire off and see if brake lights work. If not, then the other switch controls the cruise control disconnect and engage..I you have a DC test light check to see if power is on on both side of the switch with brake pedal up. If so, depress pedal and check power on the other side there should be none, if there is the switch is defective.

You'll need to have the computer scanned for trouble codes then go from there. If the check engine light was on for more than a minute there should be trouble codes stored.
The EVAP leak would not cause the engine to stall.

1 cable is for ur cruise control and does not pull unless ur cruise is on. the other 1 is ur throttle cable

possible mass air flow sensor fault, dissconnect it and see if it improves slightly to confirm or have scan for trouble codes

look in your owner's manual for the location of the cruse control fuse it is different from other fuses usually much larger

When I try to engage the cruise control, the dash light flashes, but it doesn't stay on.

Simple answer, no, it will not most likely cause any increased wear to your engine or transmission. Yes, it is normal for the engine to rev while climbing a hill while in cruise control.

The cruise is designed to be used on flat (or semi-flat) stretches of highway at 55mph or higher so you don't have to hold the fuel pedal the whole time and your foot doesn't get tired. The cruise control system will try it's best to keep your vehicle rolling at the set speed, increasing/decreasing the throttle to compensate for changes in engine load.

If you are driving with cruise on, try lightly putting your foot on the pedal and you might notice that the system will actually move the pedal itself. If you are in cruise, and you come up to a large hill, try putting your foot on the pedal and getting it up the hill on your own w/o cruise then resetting cruise once you are off the hill.

Also, cruise is not supposed to be used in moderate/ thick traffic or on country roads with a lot of rolling hills. The cruise control system is a "dumb" system meaning (not that it's pointless) but it will only change the pedal as the speed changes and it has no idea what's coming up next, even while you are already on the hill.

So, it is normal operation of the cruise control to try to compensate for a hill by constantly revving up the engine and letting it fall back down to try to keep moving at the exact same speed you set it for. If this is a bother, you can always use your foot to hold the pedal while climbing the hill normally.

Don't worry, it won't cause any increased wear and tear on your vehicle. I hope this helps. Good luck and don't forget to rate! Thank you!