C182 pilot reported a temporary loss of aircraft control and flight toward terrain during initial climb due to a loosened throttle control friction lock which resulted in the throttle moving to idle position.

Narrative

As I was ascending after takeoff from ZZZ I was complying with departure instructions (turn right to 290 degrees after reaching 800 feet). Around 400 feet MSL I turned on the AP (Autopilot) which had been set to Heading and turned right to 290 degrees from the runway heading. I looked at the PFD (Primary Flight Display) and kept my scan going; I noticed that the flight director was telling me to point the nose below the horizon and then that my speed was only 75 knots. These two things were incomprehensible. I confirmed in the status bar that the FL was on and set to 90 knots. Then out the window I saw a tree and knew everything was wrong. I needed to ascend quickly; I reached for the throttle and saw it had completely retarded. It immediately struck me that the 'throttle control friction lock' was loosened and I concluded that during the maintenance the mechanic loosened the lock. I pushed the throttle in and tightened the lock. I noticed the AP was off and put it back on. I was again in control of the plane. Then I heard ATC calling me and giving me a heading. I was able to comply. They asked me if I was OK; I said yes. Before I reached ZZZ VOR they gave me a number to call. I was glad I wasn't dead and had no trouble making the call. The pilot deviation I was told was due to the fact that a Citation Jet that was landing was told to go missed due to my position. Later in the flight cruising along at 7000 feet approaching ZZZ1 on my way to ZZZ2; I realized someone had pushed the red reversion button which made the MFD (Multi-Function Display) just a copy of the PFD. I pushed the red reversion button once more and the MFD came back on normally. Maintenance was done on the plane the prior week - putting on new tires; a new gasket for the crankshaft and a new alternator; I had not flown the plane after the maintenance was completed on Day 0. Before I taxied out and also as I waited to take off I noticed things 'wrong' with the MFD (it was not displaying what it normally did). I assumed maintenance had set it differently. I believed I could return it to the prior setting when I got back on the ground and had the full G1000 manual to look at (I did look at the abbreviated book in the plane). I was on an IFR flight. I had fully prepared; earlier I created my own checklist. Low ceilings at ZZZ worried me. I had taken off with similar ceilings years ago only to find out; when I landed; that an experienced pilot and college classmate took off from ZZZ two hours before me; and had crashed.Information shows I started going off course at XA:39:50 and descending at XA:40:06. I descended from 950 feet to 675 feet by XA:41:10 when I started ascending again. When I ascended I regained control of the plane and within seconds thereafter the AP was back on; set to heading. It was not until XA:41:58 however that I fully complied with the heading direction I was given by ATC (on the first heading I turned right instead of left as directed; I quickly noticed my error and corrected it). By XA:42:30 I was on the 180 heading I was given and climbing to 7000 feet.