While braking our 2002 Syurn Ion the engine started to race as if it wanted to take off it was very scarey because we were braking

SOUNDS LIKE ONE PROBLEM CAUSING 2.BRAKE FEEL MUSHY? FROZEN CALIPERS HOLDING BACK TRANS-RACING MOTOR CAUSING OVERHEATING BATTERY? OR.... BAD TRANS CAUSES RACING MOTOR TO OVERHEAT BATTERY.? SOUNDS LIKE 1-(CAUSE) SLIPPING TRANS , RACING ENGINE,,BATT OVERHEATS ETC........DEPENDS ON WHICH STARTS FIRST-TRANS ISSUE, 2 ENGINE RACING, 3 HOT BATTERY? THAT EQUALS A PUZZLE READY TO BE SOLVED. IF YOUR BRAKE SYSTEM WHERE IN GOOD SHAPE (EMERG BK TOO) I WOULD LEAN TOWARD THE TRANS FROM HERE. GOOD LUCK, FRANK M (PS, DONT KEEP CHANGING YOUR BATT BECAUSE OF THIS,THE ALTERNATOR IS OVERCHARGING THE BATT DUE TO THE RACING OF THE ENGINE DUE TO EVERYTHING ELSE. GO FOR THE CORE!

I would be looking for a vacumn hose leaking. The cold engine needs a rich mixture and braking uses the vacumn booster causing the mixure to lean. A warm engine races with the extra air.

A few possibilities:

1. Defective throttle position sensor (TPS);
2. Bad idle bypass circuit or idle circuit solenoid;
3. Cracked intake manifold, throttle body assembly, or bad throttle body gasket (most likely);
4. Serious vacuum leak somewhere.

have you tried at all to reset the program of the automatic transmission ? Always remember that even a simple connector been removed for second and re connected always needs adaptation before starting the car VW. Try to do the automatic transmission with adaptation.

Idle control selanoid

check the brake booster and vac supply to it. big hose on the booster.

If it was like mine, It sounds like a semi truck instead of a SUV.
It was my fan clutch staying engaged, replace it and everything was back to normal.

Try pulling the engine coolant temp sensor, They often crack not sure why but the ceramic tip cracks makes the car hard to start, the car's idle may race while shifting gears, and often smokes. The sensor is on the right side of the engine when looking at it on the head. Easy to change and get too

No O2 sensors don't cause any kind of issue like idle speed concerns, I have 30 years of expeariance to back me up on this

It may be the cruise control cable - I had a vehicle do this to me before. The engine raced as soon as I started it, even in park. A couple of times, it stopped racing - then I pressed the gas pedal, and the RPMs did not drop when I released the pedal.
If it acts somewhat like that, check under the hood and find the cruise control system - it is most likely a 3-4" diameter, 5-6" long cylinder-like object mounted on top of the engine with a long cable coming out of it going toward the back of the engine. Check all of the clips on the cable and make sure they are intact, then make sure the cable is fully attached to the throttle body at the end. My cable came loose and got itself wedged in the throttle body, preventing the throttle from closing.
If the cable seems fine, check for other obstructions on the throttle body - there may be something else holding it. It may help to have somebody inside the car pressing and releasing the gas pedal (engine off), so you can see whether it fully opens and closes.