Engine idles high after backfire?

Whilst towing a heavy load I roll jump started down a steep hill in first gear. I only rolled a couple of meters then jumped it. The engine shuddered a few times, fired up and almost simultaneously backfired from the engine with such force it swelled the bonnet I swear; and blew off the top plastic cover of the box where the air goes to the manifold. This was factory glued down I believe. The cloud of smoke which plumed out from under the bonnet was immense and the explosion was so loud that all the neighbors came running out. I would have sworn I'd blown the engine but surprisingly it started 1st pop. That's when it started going straight up to 3 or 4 thousand revs, maybe higher, and just stays there. I have replaced the idle control, throttle control, and I think the third was air flow sensor. Don't quote me on that last sensor but I did replace the three most recommended ones, I also glued the lid back on, all to no avail as nothing changed. I'm still searching for any air or vacuum leaks. Is it likely a small leak would cause such a high rev though?