Hi, also an Optra 1.6 2004 owner here... manual lang nga. Got it also, 2nd hand * 56k mileage...
My optra is still in perfect condition and I do not have any plans of changing or selling it
because I love the ride, I like its built (maski sa banggaan) and I feel more confident
compared to other cars of same level.
My optra is running now at 100+k... experienced before the same, rpm going down...
It can only be of three(3), the sensor, some small hose at the engines top, and/or the timing...
(as per what I've experienced)
Spending much for casa is normal for you, hey, remember, you do not have yet the proper
information what to do. And it is normal for a 2nd hand car to have the trouble because in
the first place you also do not have the idea of the entire history of the car. That is the
difference of buying a car with a new unit...
Also, the life of a car also depends on how it is being used and how it is being maintained.
Better see Mario...0918-7801507, he's the mechanic who resolved all the issues in my optra
which some are what you've been experiencing now.