So what could THIS car problem be?

Factual Questions
1

This afternoon I was driving my 2003 Sonata from Olympia up to Seattle for a show and an overnight stay. Just short of downtown I hit traffic. As the traffic was clearing I started accelerating - and as I was in third gear, the check engine light came on, my engine started vibrating, and I found that I couldn’t accelerate past 40 MPH. When I switched from auto over to manual I found that I could seemingly shift up and down just fine, but the car refused to go faster than 40 no matter how far down I pushed the pedal, the RPM meter holding steady as if I was in gear at 40 and not trying to go faster. I promptly got off the freeway and made it to my hotel. I found I could still start the car just fine, but the problem persisted. The vibrating seems to persist whether I’m idling or accelerating, but seems to level off a bit when I’m at speed. I checked my fluids when I parked and they seemed to be at good levels and not too dirty.

Google suggests my car is in something called “limp mode” where the car’s computer has detected a serious fault and is keeping my car in low gear so that I can get it serviced before it breaks down. After I check out in the morning I intend to find a nearby service shop to get her checked out. I may have to take a train back home if it’s going to be an involved repair. How serious a repair am I likely looking at here? Fortunately, I just got paid so I should be able to afford a repair up to around $1200 or so (if I go hungry and let some of my bills slide), but I’m wondering what I ought to be expecting.

2

I don’t know anything about Sonatas, bit I had a similar problem with my old Saturn. It was the valve body that sits on top of the transmission. Was pretty simple to replace. At any rate, the cost of the repair will depends on what has failed and how costly it is to replace, obviously. You need to get it diagnosed by an honest mechanic.

3

WAG is it could be a failed camshaft or crankshaft position sensor, or a fault in their respective circuits.

4

Go to a Pep Boys and they will plug into the onboard OBDII port to read what triggered the check engine light for free. That won’t fix it but if we know the error code(s) we could be more help.

5

I wound up dropping the car at a mechanic in downtown Seattle that had good reviews online and was close enough to my hotel that I figured I could drive it there without doing any further potential damage.

They were backlogged, so I’m not gonna hear from them until Monday. I figure best case is this costs me a few hundred bucks, worst case is it costs more than the car is worth and I’m better off renting a car to drive back up and collect my things out of it before I have it junked, and then see if I can get a newer used car financed.