Ok have a Mazda protege 2000 1.6l and the check engine light is on for p0171 which is system to lean, before i had this code though 1 month ago i had a check engine light p1170 for a 02 sensor but the code was intermittent and then p0171 came on but the p1170 cleared and never came back when i reseted the ECU but the p0171 code came back and only that code. The car starts perfect every time, it just idles rough esspically in idle or slow speed with drive or reverse. I did the MAF test by removing the MAF sensor and starting the car and the car started but died instantly and i unplugged it while the car was running but the Idle seem to have gotten just a little worse but the engine never shutted off. Also i cleaned the MAF sensor with maf cleaner and it still idles rough I sprayed carb cleaner on the intake manifold and all the vacuum lines egr etc and no vaccumm leaks......

However I adjusted the idle to about 800rpm and as i was adjusting the idle through the idle screw i heard like loud sucking vaccumm hover kinda noise right at the air filter box as i adjusted the idle higher the noise got louder and as i adjusted the idle lower to spec (700rpm) the noise got quieter. is this normal? or have i found the route to my problem?


Here are my frame data results from my obd2 scanner:

Fuel Status = 0 byte
Engine Load = 47.451 %
Engine Coolant Temperature = 192.2 °F
Fuel Trim Bank 1 Short Term = 12.5 %
Fuel Trim Bank 1 Long Term = 25 %
Engine RPM = 2,302.5 rpm
Speed (OBD) = 29.826 mph

Also MAFS at idle is reading somewhere between 2.5-3.0 g/s is that normal?

what could be the problem?

Also car runs on closed loop and open loop normally does that exclude the o2 sensors?

Also changed PCV valve, air filter, spark plug and wires and coils and still have rough idle.

 

Most likely the air intake tube is cracked. Wrap it with duct tape.

 

Intake hose is fine and seems to have been replaced by the previous owner with a dorman one.

Also this car only has 152,000 miles on the odo

 

Also those anyone know what this cable connection go to when i got the car 2 months ago that's how it was. Did the previous owner bypass something? I tried seeing where it connects to and i don't see anywhere where it connects too.

 

I looked at your picture. I don't see what is disconnected. The electrical part has to do with the fuel pressure regulator.

 

WTF is a "Dorman" one.
Is MAF sensor in a different spot? ie: on a bend?
Is diameter bigger than stock which may cause a lean code?
You definitely have enough mileage for the O2 sesnors to be changed.

You also don't need an external vac leak to have a vac leak. You could have an internal vac leak from your brake booster. Pinch off the line to see if it idles better.

A throttle body cleaning would also help @ idle.

 

"Dorman Solutions" is an after market, lower cost parts maker. Many of their parts are good quality. Some are questionable.

 

Tanprotege i already checked for vaccumm leaks by using carb cleaner i sprayed every vacuum line, egr, intake mani, etc no idle change.

Ok guys so i decided for the hell of it to replace my maf sensor so i the cleared engine code using obd2 torque app on my phone drove about 100 miles total today engine light has not come on and there is no pending codes. But rough idle is still there was i suppose to disconnect the battery negative cable while replacing maf sensor?

because i didn't. It looks like the obd2 scanner didn't reset the ecu but only cleared the codes because all the emission (egr, 02 sensor, cat, etc) components still show complete i know it can take hundreds of miles for some of them to show complete.

By using a obd2 scanner to clear the codes is that even resetting the ecu?

 

Clearing the code is the same as resetting the computer. You confused the term with re-programming the computer.
If you want to be absolutely sure pull the battery negative, then turn on the lights, or step on the brake to drain residual voltage from the system. then reconnect the battery. Now the computer needs to relearn. Search for "drive cycle" to speed this up.

Now we go into the twilight zone.....we don't know what's going on.

There is one easy comprehensive way to clean up the engine: When the tank is half full add 1 gal of lacquer thinner, NOT PAINT THINNER!, to the tank, then drive for about 100 miles. Just keep it below 5000 rpm. Then fill 'er up.

The solvents in the lacquer thinner will clean the fuel system, the valves, the O2 sensors and the catalytic converter. I have done it on 3 of our cars with no side effects. It made all of them run nicer. I think it is safe to do it every 100K miles.

If the code returns you missed a vacuum leak or an O2 sensor may be faulty.

 

lacquer thinner? Woow not sure if i want to put that in my car.

Ok update so i replaced the MAFS with a rebuilt cardone brand one, the engine light has been off for about 300 miles not even with one pending code, rough idle is still there, car drives perfect. All my emission monitors are complete. MPG seems to have increased but that damn rough idle is still there i monitored fuel trims while driving and the fuel trims have improved hell of a lot since the MAFS change while i was driving today the Long fuel trim was averaging around 5 to 8% and short fuel trims between -5 to 8%. I checked motor mounts i think they are fine.

What could make car have rough idle with no check engine light?

(This car starts perfect all the time)