Car runs sluggish and 21MPG performance :(

[yami]

I have a Mazda Protege, 1999, Automatic Transmission. It is in really good condition. A few month ago I purchased it used, it had 3 previous owners and CarFax showed it was well maintained by the first owner who had it for almost 8 years. Last two owners, I have no clue.
Afetr buying it, I changed its Timing Belt for the first time in 123500 Miles. Everything is fine but the car is Sluggish and "it feels" like I am driving it with hand brake half on. Initial acceleration is good (especially without any other passengers) but after few seconds the transmission shifts up, I miss acceleration and it runs like a very old car. Also gas mileage is 21 MPG (for City/Hwy mix) which I think is not good. Wonderfully its MPG drops a little bit in all Highway trips! Air Filter is good too.
Despite I know my car is old but still I want to fix this problem. People say it would be due to Tuning or Front Wheels Alignment or Injection Computer failure but these are just guesses. Thanks for any advice.

ps. I posted this to few Protege clubs, I hope it is not against forum policy.

[goldstar]

Welcome to CP.

It's certainly not against Forum policy for you to solicit as many sources of information as possible to solve a problem. The more inquires you make the greater the possibility of finding a solution.

Without further information, my guess is that the A/T is at fault. Good luck with finding the answer.

Happy Motoring!

[yami]

Pardon me, what is A/T?
Sorry I am very newbie to cars :/

[nerd racing]

automatic transmission.

[Ace]

you sure the timing is correct?

[MazdaNoob]

is the hold light flashing ?

[yami]

Honestly I thought about it before but:

1- My mechanic who changed Timing Belt is really professional (but greedy!) then I don't think he makes such a big mistake.
2- Both Engine and Transmission are working very smooth (by their sound).

Anyway I do not know how can I check Timing. Do you think a Tune Up service would help a lot? I am new in US and I scare mechanic rips me off because I am not local and I don't know about cars a lot. Whatever he says I will have to agree. It is why I try to diagnose as much as possible then if he says I need to change your Transmission, I say NO!!

If you mean Hand Brake light by "Hold Light", of course not! I am very sensitive to Hand Brake and check it twice when I drive.

[Ace]

Where are you located in Florida? Does it feel like its misfiring at all?

[yami]

I am in near West Palm Beach. Honestly no. Engine works very smooth. No prrt prrt prrt sound while working!

ALSO MY ENGINE CHECK IS ON but I diagnosed it and it is "only" Catalyst Converter error. I don't think it has anything related to my problem.

UPDATE: A friend called an suggested to focus on O2 Sensor and catalyst Converter stuff because he thinks maybe O2 Sensor is dead or Catalyst Converter is very clogged BUT how can I check them before taking car to mechanic, I have no idea.

Update 2: If it would be Catalyst Converter being clogged, can I just remove it? It is $350 and honestly I have not money to buy new one

[Ace]

if it is your cat that is clogged you will have a check engine light if you remove it. Not to mention most shops will not remove a cat unless you're installing another in it's place as it's illegal.

[yami]

Do you think that I can put something like cleaners in my gas tank and drive a long trip to unclog Catalyst Converter? I don't know, something like those Home Brewed Fuel Additives made from lots of Xyline, Toulene, etc?
It would be pain in *** to spend this money in this unemployment condition and worse if it does not help at the end!!

[nerd racing]

a clogged cat will cause the engine to run crappy, could glow cherry red, or make a whistling sound out the exhaust. Is the O2 code bank 1 or bank 2? a bad O2 on an OBDII engine will cause the issues you are describing.

[yami]

I remember the Only error in Check Engine was this:

P0420: Catalyst System Efficiency Below Threshold (Bank 1)

Is it related to O2 Sensor!!??

[goldstar]

Warmup Catalyst System Efficiency Below Threshold

Possible Causes from the Factory Service Manual:
Catalytic convertor deterioration or malfunction
Exhaust gas leakage
O₂ sensor (front) malfunction
Looseness of O₂ sensor (either front or rear)

I would check the condition of the front O₂ sensor first.

Happy Motoring!

[yami]

Thank you Goldstar and everybody else
Last question then, Where is Front O2 Sensor? I think I can find rear one but I don't know where is front one.