Toyota Lexcen Problems

YOUR car is a rebadged VS Holden Commodore built by Holden for Toyota when Holden and Toyota were sharing models. The headlining dropping is not a common problem, though it was once fairly common in older cars. Take it to a trimmer and have them refit it, making sure it is fitted correctly.

No, using an injector cleaner would only help if you were running on petrol, it would have no effect at all if you were running on gas. I would suspect that the engine is tired and in need of a freshen up, particularly if it's been running on gas for some time. Installing new plugs and leads would help, but I would suggest you have the compression checked. That would tell you if the valves are sticking, or even leaking.