Hey All, My 99 Protege (1.6L) is exhibiting all this trouble. I also was getting the P0171 code. I replaced the MAF since mine was dated before July 2000, and the code seems to have gone away, but not the diveability issues. I thought maybe the EGR was dirty, but in reading the logs here, I am not sure since the trouble happens at acceleration and with cold startup issues (stalling). Any other suggestions? Coil packs maybe? Any suggestions on how to test those? They are a bit expensive, so I don't want to just start throwing things at this. The dealer was not a lot of help...

 

Couple of things you might want to take a look at Gherrin.
The symptoms you are describing sound much more like an ignition missfire than anything else like EGR or O2 sensor.

Do you still have the old spark plugs?? If you do then check the white ceramic portion of the plug where plug wire boot would contact. Look for a black or grayish line that runs from the top tip down to the base. You also want to check each of the spark plug boots on the inside for this line. Harder to see inside the plug boot. Somewhat common for a 'carbon track' to get burned into both of these areas allowing spark to short directly to ground. If only the plug is replaced then the track is still left on inside the plug boot and you will not have eliminated the whole problem. Might even already be starting to transfer onto the new plugs so give them a look as well.

Also want to check for any vacuum leaks paying particular attention to the intake manifold gasket. The P0171 system too lean may have been due to faulty MAF which is probable but could also be from a vacuum leak. If warm idle is good and smooth then would suspect this less likely.

 

Thanks for the advice. I do have the old plugs, and I did not see the carbon line that you mention, but there was a lot of odd discoloration on the contact tips. I will go ahead and replace the cables to see if that helps.

The warm idle is pretty smooth, and the car seems to run fine except at the specific points mentioned earlier; hard acceleration, and maintaining speed, particularly climbing small rises on the road. After replacing the cables this afternoon, I'll check vacuum as well, just in case.

Thanks again...

 

Well....now the dreaded P0171 code is back. obviously the MAF sensor did not resolve that either...

 

Well, just as a bit of closure, it looks like there were multiple issues. After replacing the MAF sensor before, I ran a full cycle of Sea Foam and found that the Air Intake Hose had multiple leaks causing unregulated air intake isues. After fixing that plus the previous items all seems to be well again. Keeping my fingers crossed...

Thanks for the help.

 

Cracked intake hose would definitely contribute to the P0171 Gherrin. Wonder why it was not noticed and noted when the MAF was replaced.[:@].
Keeping fingers crossed with you.

 

I did notice the intake hose and taped the cracked area temporarily at the time I replaced the sensor, both of which drastically improved the issue, but it turned out there were other, smaller leaks that I missed, plus a fair amount of carbon buildup in the throttle body. I assume that the buildup may extend into the injectors, so I ran the Sea Foam just to complete the job. I have a new intake hose, and will replace that today. Thanks for keeping an eye on my updates...