I’ve been through it myself, would come on intermittently, sometimes half way through a long drive, sometimes immediately after turning the car on. I had Mick at diamond diagnose, he checked the wiring and didn’t find any faults, then identified the throttle body as at fault. Bought a brand new one to avoid any hassle and issue disappeared for months. It then came back, I bought a verified low mileage pedal (not available new anymore), issue still present, so I bought a used engine ECU and had it virginised at EFI, replaced ECU and no more limp mode in over a year since. My car had a battery that was too large though and didn’t have the proper positive terminal cover, so I suspect it managed to short the ECU at some point. I read an old thread where that happened to someone else.
Wiring faults are apparently way more common though, so I’d get that looked into first, and a brand new throttle body is a good way of properly ruling that out, rather than rolling the dice on a 20 year old used one.