this post is for a friend with an 04' "r".
Car was fine only with a long running cruise control failure (fault). So he was driving and he said the he took foot off the gas and the car kept going like he was on the gas so he shut the car off in gear now it is in limp mode and showing like 5 codes including cylinder 2 misfire and cat code and maf code. I know the codes could be from shutting the car off in gear. Any suggestions beside battery reset, what could cause this surging forward even though off gas?

Check battery first...

Sticking throttle maybe? Would throw codes and likely get very upset. I suppose clear codes and see which one(s) flag first.

Any (engine) mods on the car?

A real possibility is a failing battery as it is needed even when driving.

The STR is a drive by wire throttle body. Did your friend happen to shroom at the time of the alleged unprovoked surge?

It's a medical question.

Check the floor mat. It sounds dumb but it's easy to do.
.
.
.

Lol! Clubairth, you're a genius.

shroom? bfgross. Don't know what that means. But I told him check the battery first, and reset it. I won't know the outcome, it was my car. And no modifications. Someone did mention something about possibly throttle body issue. But doubt it with 7 random codes. But I could b wrong

Lol, mushrooms...as in hallucinogens. Can't see that a stud
Ch
K throttle body could cause this except for some internal mechanical issue. Remember years ago when Audi had similar issues that caused crashes etc.?

I have a 2000 XK8 and I've had the similar thing occur. Driving along at low speed 20-40 kph) and the engine climbs to about 3000 RPM without contact on the accelerator. It settles down and the issue passes after a couple of minutes. This occurred a couple of times. I am still trying to resolve it.
Recently, the engine has been cyclically running up/slowing to idle at startup.

Which engine? Auto/manual? Etc...

Sounds like an air leak. Get cheap OBD tool and report LTFTs at idle & 2500rpm, parked.