Hey guys, first time posting after digging around the forums a while looking for a solution. The car is a 99 Protege 1.6L with 205k on it. Took the car in for an oil change and the CEL came on shortly thereafter. Originally I suspected that it was fishy but now not so much since there was no air filter replacement. The code is system too lean, bank 1. Car drives fine with no real noticeable issues or loss of power. Sometimes I feel the idle getting a little quirky at stop lights (of course theres no tach on this stupid machine so who knows...). In fact the last two times the light came on I was stopped at a light idling.

I've already spent some time with diagnosing so I'll bring you up to speed.
- intake (accordian) hose was duct taped when I bought it so that was the first to go. New OEM part and it still came back.
- checked for vacuum leaks, everything looks good. Intake manifold gasket looked to be brittle and cracking in the exposed sections so I sprayed some brake clean around it to see if it idled different. No changes, seems fine.
- Cleaned the MAF sensor, it was looking pretty dirty so I figured I had it this time but the light came back again.
- Checked PCV valve, i can hear it rattle when shaken so i assume its functional.
- disconnected MAF and went for a ride. Car idled fine but once I put it in gear and drove it was extremely unresponsive and jerky. Plugged that back in right away
- banged head against wall

Seems to me like I've taken care of the small easy fixes which makes me afraid of what is to come. I think I'll replace the PCV valve and pray to the auto-gods just cuz its so cheap but I'm running out of ideas. I don't have any equipment for reading fuel trims or pressure etc so I'd have to take it to a shop if it comes to that.

If anyone can throw down some knowledge it would be much appreciated. Obviously I've tried to do my hw on this one and it's not going my way. Thanks in advance!

 

mazman9: You did all the things that I would have done. However I avoid banging the head against the wall. It is not good for the wall!

Pull all the small vacuum hoses and replace them with new hose from the reel. Buy 15" for a few bucks. Sometimes the hoses get to hard they can't seal around the nipple.
Clean the throttle body with throttle body cleaner. Open up the EGR passages and clean the EGR valve. Make sure the nipple is open at the back of the intake manifold where vacuum hose for the EGR boost sensor attaches. Poke in there with a strong wire.
Look for any cracks on the exhaust side. The P0171 is based on too much O2 at the sensor. It does not know where the O2 comes from.
Check the fuel pressure. You can loan a gauge form the parts store.

Keep at it, you will find it.

 

Thanks tanprotege, those are exactly the kind of small things I wanted to check before going further. Didn't have much time today but I was able to replace most of the vacuum lines, the pcv, and clean out the throttle body. Will get around to the rest eventually, but for now I can drive on it and see if it still comes back.

The EGR was tough to get to. It seems to be attached by phillips screws to the bottom of the throttle body if im looking at the right part? Anyways after many thousands of miles its nearly impossible to get off without stripping the head so I left it for now.

Might be back at it tomorrow if I have time.

 

If you are not sure how something looks like do an image search.

and here is what a bad one looks like:

In my 98 protege 1.5L it is attached with 2 hex bolts (10mm socket) on the side of the TB, lower part. You need a new gasket ($ 3.00 or so).

 

Ah i see, I think I was looking at the IAC valve. Might not be a bad idea to clean that either? When I called my local mazda looking for an EGR gasket he said manual proteges dont have them...? I'm thinking that is a load of bs but would transmission have any effect on having an EGR?

 

Yeah, your mazda dealer didn't torque is head down correctly that day.

Go to a parts store for the gasket.
Use the B-12 chemtool on the EGR valve. My stuff was so dry no solvent had an effect. I scraped it out. Make sure the pindle moves easily.

Leave the IAC alone. When you clean the TB you can flood the IAC valve with TB cleaner from inside the barrel.

 

Woah, in an interesting turn of events the dealer was actually right..? See the discussion in the following link:

I have no EGR Valve? [Archive] - Mazdas247.com

So yeah, my EGR couldn't be any cleaner because it doesn't exist I was trying to find it for a while and nothing was adding up lol sometimes the easiest solution is the one you overlook. To that end I've been thinking lately that maybe it just is an 02 sensor? It would make sense with there being no real adverse driving problems. Plus now that I think about it I think she runs just a tad rougher after the CEL comes on. My thought is 02 feeding the wrong signals to the computer so after disconnecting the battery terminal which resets the cpu it runs okay and then over time the 02 applies the wrong trims to a point where the CEL comes on and it doesn't run perfect?

One thing that doesn't make sense is that fuel mileage seems to be unchanged (I've heard bad 02 sensor = worse mileage). Again, could be my imagination so I'd like a way to comfirm something before dropping 150$ for what could be a new paper weight. If you pull an 02 sensor can you bring it somewhere to be tested or is it really just buy one and cross your fingers?

Thanks for workin with me tanprotege you've been a big help thus far. If there's any other maintenance items you can think of that might be a better option, I'm definitely open to it. Also, I must admit, I haven't checked for an exhaust leak yet for I haven't had time to remove the heat shield etc.

 

Don't kill the messenger. your 02 sensor is telling you something. And it's probably the truth.
There is too much O2. When the check engine light comes on the computer switches ot "open loop" which means it ignores most sensor data and uses programmed data instead. That leads to running rich. Running rich has less dire consequences that running lean. Running rich may save your engine but it puts a big load on the catalytic converters. You feel that switch to open loop.
You most likely have a vacuum leak. There are Youtubes on finding vacuum leaks.

I am glad Mazda found a way to eliminate those troublesome EGR systems. Are you in Canada?

 

Hmmmm, either smart people are in Canada or Freaks?

I'm from Canada and i'm sometimes smart, sometimes a freak, mostly logical.

I've heard of by-passing the EGR system by having it routed to intake filter rather than directly in to intake (prevents bits from re-entering engine). I'm not certain if just capping off the EGR really works, or if that is your problem.

 

noggin: the EGR is one problem he does not have.Good for him!

He has a lean condition which pops up when idling. Incidentally the when idling the vacuum is very strong. That means to me he needs to look for a small vacuum leak. He should try several methods.

Interesting self assessment, btw.