Hi all,

We have a 2001 MPV with 151k miles on it, which we've owned since it was new. We still like it a lot, but for the past couple of years it has been causing extra stress around inspection time, due to a persistent CEL. After checking for codes at Autozone and being informed it was "random multiple misfires", I had my mechanic check it out. He couldn't really find anything, but mentioned the '02 and '03 recalls for the PCV hose and that another possibility was the intake manifold gaskets, but that that would probably be a fairly pricey job.

I finally decided it would be worth it to have my own OBD reader and bought one and pulled the codes myself. The main one causing the CEL is P0174 system too lean (Bank 1), but there are pending codes of P0171 system too lean (Bank 2) and P0706 transmission range sensor circuit range/performance. As I said, the van has been running well enough that if it weren't for the CEL, we'd just keep on driving it and doing our normal routine maintenance. But we have an inspection coming up and it won't pass with that CEL on. Last year when it happened, the light happened to go off right around inspection time, so we hustled down to get a sticker during that window of opportunity. I can't guarantee we'll be so lucky this year. Incidentally, the light came back on in a few days.

BTW, my son is the one who normally drives the vehicle, but since he's been home from college I've had more of an opportunity to get an idea of the problem. So in driving it again today and paying close attention, I have noticed a couple of symptoms, which may help your diagnosis.

• When stopped and in gear, I can sense a slight bucking as if it's just idling unevenly, which I guess is confirmed by...

• When parked and idling, it will idle a little high for about :30, then die down to a low idle for about :15, then back up to higher idle for another :30, and back to low for about :15 again, and that cycle continues.

I don't really hear any air or sucking sound when I stick my head in the engine compartment, but that could be just the sound of the engine itself masking anything else.

Anyway, I'm trying to get an idea of what it might cost for the dealer to do the intake manifold gaskets replacement, or if there are other cheaper steps I can try first to get rid of that dang light and pass inspection. I evenbought a couple of bottles of Techron to dump in the tank on the off chance that might help.

Thanks in advance for any advice or suggestions.

 

I had similar issues with miss fires and lean codes.

The dealer first replaced one ingnition coil and an electronic module on the transmission. CEL went back on 2 weeks after. They changed two other coils. Again the CEL went back on after a week. I purchased an OBD code reader. The codes that I got were for lean running conditions. I looked at some forums and they indicated that this may relate to the mass air flow meter. I cleaned it with contact cleaner and code was cleared for a few days. It went on again so I cleaned the sensor again but left the wire filaments immersed in the solution for about 10-minutes. Left the wire to dry before re-installing. I cleared the CEL but the engine still ran rough at idel with no code display.

When running rough at idle I would turn on the A/C and this would get rid of the rough engine idle. Other forums indicated the PCV hose but I did not replace because based on the instructions which I had it seemed like it was hard. A few weeks down the road the CEL went back on. Now it was flashing. When I applied the brakes more then once the pedal would bottom out and breaking was very weak. I got several other codes Random miss fires and lean operating conditions.

Agian on some forums the solution pointed again to the PCV hose. The breaking issue was related to a loss of vacuum.

I checked the PCV hose by passing my hand behind the air manifold and the fire wall. Its a very tight fit. Behind there the PCV hose makes a 90 degree turn towards the engine. If the hose is in good condition the bend should be smooth. In my case the material was sucked into the hole and you could feel a crevise in the hose. I went and purchased a new one for $120CDN at the Mazda dealership. It took about an hour to replace. After that the braking is back to normal and the rough idling is gone. No CEL for two month now.

My MPV is a 2002 the PCV hose was replaced in 2004 as part of a recall. The new model PCV is re-inforced so hopefully this time it will last for a longer period of time.

 

The following was specific to Proteges, but may nonetheless be helpful in locating and remedying sporadic "lean mixture" CEL appearances. It was a result of my own experience with this in response to an item by Adam S
Original thread:

04-13-2009, 11:30 AM
Adam S
Junior Member
I have a 2000 Mazda Protege, 1.8L with 5 speed manual transmission @ 190,000 kms which described the problems, and in the same item,
Response:
04-13-2009, 11:06 PM
oldeng
Senior Member

Hi. That code is familiar to owners of older Proteges. You don't state whether your warmed up idle speed is normal and stable (700 rpm. +/-) .
I note you state distance run in Km., suggesting you (like me) are a Canuckstani.
Good, I own a '99 Protege (93,000Km.) lots of problems (cured) and currently in great shape, also I have the 2000 Protege 1.8L shop manual.
Living near Montreal, I have to contend not only with the arctic winters, but also with the most aggressive road salt mix known to man. This has led to problems the shop manual never even dreamed of.
Before getting into serious money, I suggest you look very carefully at that ducting between the air filter unit and the engine intake. Unclip the air filter, and don't be hesitant about really moving it around a bit either. The air duct has a habit of getting brittle and splitting apart. What happens is it seals at rest, the engine is then torqued on the mounts as you engage gears, then the movement of the engine opens the split, letting air (which the MAF doesn't "see") into the engine, making the mixture way too lean. Now the engine complains, rocking to and fro on its mounts, making the ducting work like an accordion (with a split bellows), so the whole show just rocks (literally) on the engine mounts. This you can fix with duct tape.
If the duct is OK, then next you get yourself a 2ft. piece of tubing (even garden hose works), and use it like a stethoscope to "earball" your way around all of the plumbing which is connected eventually to either the throttle body or the intake manifold, listening for sneak leaks. (The underside of the hood has a "map" of the vacuum circuits.)

Another common weirdo of the Protege is that bad ignition hickups can throw the ECU for a loop. Get yourself a spray can of contact cleaner (which is good for cleaning the MAF anyway), and remove the two connectors at the front of the coil packs. Give those connectors a really good cleaning with the spray, and clean the dirt off the coil packs while you wait for the contact cleaner to do its job.
While you're at it , disconnect the two connectors on the air filter/MAF assembly, (MAF and Air Temp.) and squirt them too. Then take the tube off the spray can and shoot a good shot down into the MAF itself too.
Now go back to the coils, spray them with WD40 and clean them up well, using an old toothbrush, rag or whatever.
Next, check the condition of your plug harness. If it's old, it will arc onto any metal it gets close to, so make sure all of the wires are 1/4" or so clear of metal and each other, and that the plastic spacers which slide onto the mounting tabs on the engine head, are clean and in good shape too.
Now put the four connectors back where they belong, but connect and disconnect them a few times to ensure good contact.
Start your engine, warm it up, note the idle speed ( should be 700 rpm. and stable to +/- 50 or so) , go for a run and (if you've got it) check out your cruise control.
Now call it end of phase one, and post your findings on this thread.

If you still have problems, we will need some maintenance history details, last timing belt change, spark plug, battery/alternator history, upstream O2 sensor etc.
Also, since P0171 is a "catch all" code, it often has subordinate freeze frame codes behind it which are very useful in pinpointing the source of the mischief, so a visit to a competent Mazda agent for diagnosis with a hardcopy printout of ALL OF THE CODES might help.

(As much as I hate doing this, and at the risk of making a fool of myself (again) on this forum, right now I'd put my money on a split in the main air duct, with the ignition system a close second, provided of course that you have been observing the scheduled maintenance regime).

You may wish to adapt this treatment to the venerable MPVs to see if it removes some of the aggravation. Good luck.