Hello from Port of Spain, Trinidad...
I have a 1989 Volvo 240 GL that I bought in New York many years ago.
I have since relocated to Port of Spain, Trinidad in the Caribbean. The engine and Transmission is great with over 300,000 miles registered. My problem is black exhaust and a rough idle. I have replaced a good many parts since the problem started and given the vehicle is 26 years old.

These include the • fuel pump • fuel pump relay • MAF sensor • Spark plugs and wires • roto • fuel filter • fuel pressure regulator • trottle body switch
• cleaned the trottle body.

I then took the car for test drive and found that it lost power going up a hill, so I changed gears to 1St and the power came back, but my break peddle became hard. I pulled to the road side. Then it did not start. I waited for an hour and tried starting again. This time it started, I am confused about this as the mechanics are making money while my mind is screaming: time for a new car. I don't want to sell it. Can you help me?

 

Welcome to the forum.

Please post questions about your car in your cars section. You're much more likely to have someone jump in with help. "New Member" isn't for help it's just for introducing yourself and your vehicle.
Moved to 240

 

are you using a lot of oil?

at this point, I think I'd start by pulling all 4 spark plugs and checking what color they are, and doing a compression test on all 4 cylinders.

it sounds like you replaced a lot of parts without doing any tests to see if those parts were bad. for example, if your fuel pump relay or fuel pump is bad, the engine won't run at all. throttle body switches can be tested with a simple ohm meter test.

"brake pedal becoming hard", that sounds like your brake booster isn't getting vacuum, you should check the vacuum hose and the vacuum fitting on the booster which has a one-way valve in it. if that big vacuum hose is open to the air, the engine will probably run very poorly.