Steerin wheel jerks at speeds over 40 or when free wheeling down hill in my 98 camry

It may be your fuel regulator, mine did the same thing, and the turbo should go almost down to no power while going down hill, thats normal

Seems to me that you have a hub bearing and/or cv axle gone bad. Did the ABS light come on?

It sounds like a sensor is intermittantly loosing the data stream. Since the engine light came on, I would go to a reputable shop and have them check for codes. Many auto parts stores will do this as well and sometimes for free. Can't beet free. If I were to guess I would say something like the camshaft postion sensor is going bad, Or the crankshaft postion sensor, Or something like that. The code will tell which one it is.

Good luck, and if you have any further questions please....ask!

so it has some to do with rotation. you can jack one front wheel up, set parking brakes, start the car and put in drive. which ever side make noise, that's the one you need to inspect cv-axle, wheel bearing, ect.
check any thing that turns with the wheel

have the car scanned for the codes,then get back to me,most big chain parts stores will do this for no charge

get a scanner check code sound like vechicle speed sensor.

ABS system is self monitoring.It will perform a peliminary check on itself when you first turn the key on,thats why the light stays on for about 3 secs when you first start it up. It will also perform another check on itself after you reach speed of around 8-12 mph.
For it to come on while driving it must see something wrong at the wheel speed sensors that it knows can not be correct so it is shutting itself down. It has a digital wheel sensor in each wheel that it uses to compare side to side readings. If it sees one wheel spinning faster than the other it thinks one of the wheels is locking up and it activates. Now it could be one of the wheel speed sensors is starting to go bad or it may be something as simple as one of the tires low on air. I would check all of the air pressures in the tires first to make sure the are equal and if that is ok then I would have some one hook a scan tool to it and see what trouble codes are stored in the memory of the ABS module.

sounds like lower balljoints or inner tie rod ends jack up the car try to move wheel from side to side

1 Inspect Hose (Vacuum) Misrouted, damaged, loose, or clogged vacuum hose(s) 3 Inspect Spark Plug Wire Loom - Performance Improperly adjusted or worn/malfunctioning carburetor. 4 Inspect Fuel Injector Plugged, dirty or poorly connected fuel injector. 5 Inspect Fuel Pump Improperly functioning fuel pump or circuits. 6 Inspect Hood Brace Leaking, worn, or damaged intake manifold gasket
here is a list of things to check Here to Help Shaun