You did what? Show the pictures, how you
"opened the engine". "Cleaning the valves" requires removing them from the engine head (and head must be separated from the block, so it's a "head gasket job"). I doubt you did this.
Plus, there is no "flowmeter" in this engine. You must do your homework.
Car was neglected. It needs a serious maintenance, servicing. Multiple things.
1. Intake vacuum leak. Many things, manifold itself, throttle, EVAP system solenoid valve, hoses, brake servo.
2. Idle air obstructed, blocked. Breather hoses (especially small one). Air filter.
3. Sensors: MAP (it measures temperature too), coolant temperature, oxygen (lambdas), clutch switch (computer wants to know if clutch is depressed or not).
4. Timing belt and/or valve "lash", clearances. They must be adjusted (manually, with shims) very often on the LPG (it will eat the exhaust valves fast)! Every 20000-30000 km (almost no-one does that!). Same is true for sparkplugs.
5. LPG set-up, adjustment. Check (professional LPG shop) the LPG fuel map (this should be done while driving, and ideally with extra probe/sensor in the exhaust). LPG injectors may be stuck or pressure regulator (reducer) misbehaving.
If problem is still there, isolate the LPG system (use-up the fuel completely, close the valve near the tank), fix the car on gasoline/petrol first.
6. Clutch, mechanical/hydraulic issue. Slave cylinder leak (check under the rubber boot, must be dry), air-lock, old brake fluid, bearing or fork wear.
7. Catalytic converter inefficient.
PS
For "breather hoses" and "valve clearance adjustment", go to
Guides section (page 1 & 2). Plus, search for other threads (scroll down this page, there is "Similar Threads" bar).