Guys thank you very much for your help ... yes I am new and I am not mechanic , I am a student and I don`t wanna pay more money , I need to save money more so I need your help ... I have a mechanic and he checked for vacum leak by spray , he said there is no leaking , I bought O2 Sensor bosch from Oreilly and MAF from Ebay and it was after market ... Do I need to buy it from dealer or the ECU needs to program refer to last comments .... ?

 

I agree with the Haynes manual. The fuel pressure regulator is part of the pump. X2 check fuel pressure, sounds low to me.

 

imaco: I hope you did not throw the original MAF sensor away. You can clean it, install it and test it. You can also buy one from the junk yard. These things are expensive and usually last for ever.

Car-Part.com--Used Auto Parts Market

One thing you need to consider: the maf sensor communicates with the ECU. There could be something wrong with the wiring.

But first get a fuel pressure reading and see if it is normal. The Haynes Manual has the values to look for.

Did you ever run out of gas with this car? What kind of gas do you use?

I will be patient and help you along as much as I can.
Kevinpk: thanks for helping out. There are changes from the 98 model to the 99 model that I don't know.

 

I usually go to Texaco and buy regular gas , Also I bought Chevron fuel system cleaner and after 2 3 days for filling the tank I will use it , I cleaned the original MAF with CRC but I had the same problem so I bought the after market MAF , my mechanic told me buy a new from dealer but I am worry to buy another one , he checked the parameters by the tool and he said everything is fine but in my opinion the engine rev is low ... also my friend told me clean the place where the MAF is located ... ? what do you think ?

 

Your original MAF sensor was o.k. you proofed that by replacing it with a new one and that did not change a thing. That's why I am telling you not to replace parts nilly *****.

Regular fuel may not be enough. Get at least 89 octane. Texaco, Chevron. Shell, BP, Phillips 66 and such brand names are selling "Tier1" fuels. you can safely use any of these brands. Put the fuel system cleaner in now and fill up.

Did you buy the haynes manual? Did you measure the fuel pressure? You can loan a fuel pressure gauge at the parts store using your credit card.

Did you do anything I suggested in post #12?


Also: I went through the whole thread to review what we have here:
'99 Protege 1.6L of unknown mileage.
Main complaint: low power and extremely low idle, about to stall.
P0171 (persisting)
No vacuum leaks detected.
New MAF sensor, and oxygen sensors.

You know what? I jumped on the P0171 without looking at some important basics.

How many miles are on the engine? How many miles are on the spark plugs? Do you have COPs (Coil on plugs) or a distributor? Hint: if there are no wires going to the spark plugs you have COPs.

I am asking these questions because we employ a process of elimination. the more we know the quicker we get it fixed.

 

Thanks ... I bought the car about 2000 miles ago and now the mileage is 116000 original mileage , suppose all and most of parts are old and original , I just changed MAF , O2 Sensor , Ignition coil , tires , and alternator belt . My mechanic is a master mechanic and he and another mechanic told me the car is really good and in future just you need to change the spark plugs and wire set ( they are old ) ... about Haynes manual , cause I am not mechanic and I don`t have tools here i think its not worthy for me to buy it , my mechanic connected the reader and scanner and checked parameters and he said everything is fine but I can go again and ask him give me and write on a paper all parameters and fuel pressure so I can say here ...

 

thanks imaco.

11600miles, that's roughly what I guessed (10K to 12K per year).

Most public libraries have the Haynes Manuals or the Chilton manuals. Check it out. the manuals are even useful for those who don't turn wrenches. Or buy it at Amazon, used. It's only about $20 new. And it could have saved you how much already?

Get new plugs and wires. I don't know if your engine has a distributor like mine or a coil pack. If it has a distributor get a new cap and rotor for it. Who knows, the reason for the P0171 may be connected to misfires. If these parts have been installed at the factory it is a miracle the car runs at all.

It would be helpful if you could provide us with the information from the scanner. Ask them to reset the computer or you can disconnect the battery negative and then step on the brake pedal for a few seconds, then reconnect the battery. This also resets the computer and the CEL is off. When it comes on again get a new reading.

 

I think its still a good idea to change the plugs and wires, but I think if he was misfiring it would have a misfire or rich fuel code. A new fuel filter should be a must, I believe someone earlier was on the right path with a fuel supply related problem like fuel pressure. This makes sense with low idle and lean condition. A vacuum leak would usually be a high idle and lean. After changing any items unplug your battery for about 10 minutes to reset your ecu. We are all pulling for you, hopefully you can get her fixed up with minimal $$.

 

I used a Techron cleaner and then refuel with Texaco 91 octan , reset again but I still have the problem .... I am sure there is no vacuum leak and the only problem in my car is engine rev ... it is under 750 and sometimes it comes to 400 rpm ... I am going to the mechanic to get the parameters and change my spark plugs ... what the worse code P0171

 

I don't believe you!
You could still have a vaccuum leak!
I had an internal vaccuum leak in the brake booster. The only way we figured it out was to pinch off the vac line going to the brake booster and watching the computer. After a while: i did have the odd time where pressing the brake pedal was hard, really had to press on it to barely stop --- because i did not have any help from the booster. It was code P0171!
The fix: new brake booster from Junkyard!
This took months to diagnose because it didn't happen all the time!