HELP I don't know what is wrong with my car

Car: Mitsubishi Eclipse '95 RS

Well this started happening about a year ago and I did almost everything to make it work.

Whenever I start the car in the morning, I feel the vibration. The RPM is around 1100-1200 but as it starts warming up. The RPM goes down a little bit and I feel more vibration. Then it becomes unstable for 2-3 times. I mean it goes down to 200-300 and then suddenly jumps back to almost 200 and come back to 1000. It does this almost two times whenever I start it in the morning. When the engine warms up, the rpm stays at 800-900. But when I try to give more gas, it give a brrrrrrrrrrrrrr noise from the muffler and I feel there is less power in the car. But at some point it gives a jerk and goes back to normal power. If I give more gas below 3000 RPM, it usually happens. But after 3000 RPM, it usually works like a normal car except sometime.

One time I got a check engine sign that stayed for almost 3 months and then went out couple of days ago and has not shown yet. I checked with Autozone and they said my catalytic converter is bad adn the oxygen sensor has gone bad. I checked the catalytic converter with the muffler people in the town and they told me that there is nothing wrong with it.

I changed the fuel filter and also changed the spark plugs with the double headed Bosch spark plugs but still no effect. How many fuel filters are there in Mit Eclipse 95. Is there a one next to gas tank? I heard that some car have something like that. Is there anything else I should change? What seems to be the problem? Someone please help me. I want to fix this problem before something happens to the car.
I use the 93 gas. Also I have put the fuel injection cleaner on the tank but still the problem has not been fixed.

Thanks in advance.

Check your ECU.

try the fuel injection kit that go"s through your engine ...it works alot better try that ...other than that stuff beats me

if it only does it when it is cold, you probably just got a cold engine. is the engine stock?

try your idle I had the same problem and was the idle, I tooked to a mechanic and he check the computer and he told me that the computer was sending a weack signal to the gas.
He told me that the computers is going bad and in a few a will have to replace it.
What do you think?

My Car Does The Same Sometimes. Let Me Know If U Find Out What It Is

here are some links i found for you guy's

http://www.dsm.org/how-tos/tttt/tttt3.html

http://dmtalon.v8eaters.com/ISC.html

EDIT: this is for n/t engines.

Thanks guys I think this might help me. I am gonna try it as soon as I get off from vegas and go home. That is superb. THANKS THANKS THANKS

hey ur problem is that ur throtel thingy (u know that thing on the motor) that is connected to the throtel cabel isnt adjusted ...my buddies 94 bmw had the same problem and i just tightened it and it works purfect

if you didn't already have your o2 sensor replaced that could very well be the problem, i have had the same problem with my previous cars and most of the time it was the o2 sensor.