CEL P0171 and Engine Stall Related?

Hey guys,
I just bought a 2003.5 Mazda Protege Speed at 120,000 miles. The car would stall while coasting in neutral from accelerating in gears 3, 4, or 5. Check engine light comes on. I take it auto zone, reads P0171 Bank 1. I understand the car has too much air coming in from somewhere. I don't think it's my fuel because the car accelerates great, no hesitation. My friend reads it and tests the car. He will let the car decelerate from 3, 4, or 5th gear for about 1 - 2 secs then shift to neutral. The car doesn't die! But the CEL is still on. He tells me that, the air from the turbo that recirculates from the acceleration is being pushed back into the manifold, and when I switch it to neutral really fast, the ECU doesn't account for the extra air, therefore, causing the car to die. However, if I let the air pass into the manifold in gear while having the right amount of fuel, the car won't die after I switch it to neutral. Have been driving around like this and the car seems great. He suggests I take it into performance shop and tell them to modify the ECU so that it compensates for the extra air from the turbo while in neutral. He is suggesting that the fuel injectors are being closed out too earlier form the ECU and is not compensating for the air. Been fine ever since, however, I want to get rid of the CEL. I was wondering if anyone knew weather the CEL and the stall is correlated? If I modify my ECU will the CEL go away? Are they two different problems? Or do I have a vacuum leak? My car won't stall out anymore, but I do have a drop in idle once in a while in neutral. My car doesn't die if I control it as stated above, allowing deceleration before coasting in neutral. Please help? Any suggestions?

Also note:
I did not take it to the performance shop yet. Controlling the car won't die, however, CEL goes on and off. Help?

are you completely stock?..to include BPV too? You may have a leak somewhere. Check all vacuum lines and intercooler pipes to make sure they are all tight. MSP P0171: air/fuel ratio lean bank 1
causes: low fuel pressure
large vacuum leak
dirty/defective MAF sensor
engine mechanical condition

By the way, there is no modifying the ECU. What is your friend talking about? When you let off of the gas, the throttle body closes which prevents any air from going into the intake manifold. This is why turbo cars are equipped with BPVs and BOVs. When the throttle body closes, the pressurized air from the turbo backs up against the throttle body and has no where else to go but...you guessed it..the other way. The BPV or BOV opens releasing all of that backed up air to prevent compressor surge. Your friend is saying the ECU cannot account for the extra air going into the manifold. The only time air goes into the manifold is when you are driving(foot on gas). If the ECU couldn't account for air while driving, you would not be able to drive. With that being said, it sounds like you have a BOV VTA with the symptoms you are describing. If you have a BOV vented without relocating the MAF, every time the BOV opens, it releases air that the MAF sensor did not account for causing the car to bog down or stall. This sounds like it is your problem especially since it ony happens in neutral or coasting to a stop.

you can not "retune" the ECU. you will need to install some PNP or
piggy back system to control things. and yes I would say you have an
issue that tuning the ECU wouldn't fix.

see ....^^^^^ what he said! lol

Spiced MSP,
So are you saying the Bypass Valve just throws out all the extra air? I have everything stock. Cleaned the MAF but doesn't seem to help much. The CEL is still on and it still dies from high acceleration to neutral. I will check for vacuum leaks tomorrow, but did a quick visual scan and everything looks fine. Any where I should look in vacuum leaks for MSP? I don't want to bring it into the shop since they are going to charge 80.00 plus for diagonistics which doesn't even account into the service repairs. I don't get why it wouldn't die though when I let the car decelerate a little and then shift it to neutral? I know it dies when I accelerate then shift to neutral. Where is you'all bypass valve? Where is it connected to?

Spiced MSP, engine mechanical condition refer to?

still sounds like your dumping your pressure to atmosphere when shifting ( almost like your running a BOV instead of a BPV ) that will cause this issue to the tee.
do you have a boost gauge? you can read that and see if you have a vac. leak.

Speedracer,
No, I don't have a boost gauge. I can't read the vacuum leak. Any other options? I am trying to talk it over with my friend again to see what he says. Have you run into this problem yet?

yes I have that exact same issue when I accelerate hard then shift. Thats why I mentioned venting to atmosphere. I'm running a BOV instead of the BPV and that's just one of the things you have to deal with if you don't have a relocated MAF or running the duel setup. I would work on getting that boost gauge it help locate the issue, plus I would say every MSP needs one with all the issues they develop from time to time.

Speedracer,
I am new to turbo cars and don't have a clue. Hope you don't mind answering some questions. Where would you relocate the MAF? What is the duel setup? I still don't understand why it would cause the engine to stall? The throttle closes off, so no air can enter into the intake manifold or the engine, why would the car still stall? Why would the CEL read too lean?

the MAF setup in our cars is a funny and finicky thing. It does not like pressure change and thats why we have the recirculating system instead of the BOV system stock.
when the pressure drops on the exit side of the MAF you go lean and stall. The BPV helps keep the pressure equalized during shifting.
You can relocate your MAF onto your cold side intercooler pipe. (but you will need to get an aftermarket pipe to do this) the duel setup is to run both a BPV and BOV together.

Speedracer,
"You can relocate your MAF onto your cold side intercooler pipe" meaning putting the MAF out further away from the throttle and BPV pipes? Does the BPV make any noise since it's just equalizing pressure? Where would you put the BOV if you are going duel? Should I go duel? If it is not a vacuum leak do you think the BPV is malfunctioning, or that pressure is getting to the MAF causing the engine to read lean and therefore stalling the engine?

Do you think EGR valve would cause this problem?

leex said:

Speedracer,
I am new to turbo cars and don't have a clue. Hope you don't mind answering some questions. Where would you relocate the MAF? What is the duel setup? I still don't understand why it would cause the engine to stall? The throttle closes off, so no air can enter into the intake manifold or the engine, why would the car still stall? Why would the CEL read too lean?

Click to expand...

if you are lean, you more than likely have a leak somewhere. Since you are completely stock, I bet you just have a simple leak somewhere. Plastic pipes constantly expanding and contracting in different driving conditions over time will cause things to crack and/or break. Check intercooler pipes visually and physically to make sure they are on tight and not loose at all. Check intake pipes for cracks. A boost gauge will help determine if you have a leak because looking at a boost gauge will tell us what your vacuum looks like at idle...which will tell you if you have a leak or not in most cases. More importantly, an AEM UEGO gauge could also aid in troubleshooting our cars. If you don't want to dish out the bucks for a quality boost gauge right now, you can get a cheapo from autozone for like $60 or something like that for now. To relocate the MAF, you are pretty much just cutting the cold pipe(intercooler to throttle body) and placing the MAF sensor there using two couplers and some clamps. That way it will always see a constant amount of air. If you look at my sig, you will see Im runing a dual setup. Basically, if you don't want to relocate your MAF sensor, you can run a bpv and a bov. The BOV will give you the sound you are craving if you want to hear that whoosh while the BPV will recirculate some of that air back into the intake to keep your MAF sensor happy and keep the car from stalling out. I have a BOV on the cold pipe and the stock BPV on the hot pipe. No stalling at all. By the way, "engine mechanical condition" is pretty much worst case scenario. How many miles are on the car?

The best thing I can tell ya is to search for the threads talking about the duel setup and relocating MAF. The pics and posts can get you a lot farther than I could one on one.
and do you have a pic of the engine bay for us to see if there is something not in the right place.

leex said:

Speedracer,
"You can relocate your MAF onto your cold side intercooler pipe" meaning putting the MAF out further away from the throttle and BPV pipes? Does the BPV make any noise since it's just equalizing pressure? Where would you put the BOV if you are going duel? Should I go duel? If it is not a vacuum leak do you think the BPV is malfunctioning, or that pressure is getting to the MAF causing the engine to read lean and therefore stalling the engine?

Click to expand...

you put the MAF sensor on the cold pipe a certain distance away from the throttle body but before the BOV. The BPV on a completely stock car you will not hear in most cases until you get an aftermarket intake. It's just a slightly muffled whoosh. You don't have to worry about doing a dual setup unless you just want the sound of a BOV. The stock BPV is fine until you increase boost. You will know if your BPV is malfunctioning because you will start getting compressor surge which you can hear. It is a flutter-like sound which on this forum is referred to as the "turkey". The stock BPV's inlet and outlet are not big enough to release the air quick enough to prevent compressor surge as well. If you hear the flutter on light to moderate throttle, then your BPV may be malfunctioning. But in boost, you will hear the flutter simply because of the small outlet for the BPV.

Hey,
I'll post up some pictures for you guys tomorrow. I have a question regarding Spiced MSP setup. You have the turbo pipe going stright to the MAF and filter? Where does the pipe from your throttle go? Your BPV pipes are alot bigger than mines. Hm.... I'll take some pictures tomorrow for you to see. Does that setup work pretty well?

ok, well I was searching since I had this same code thrown at me today when I wanted to really just go out and tune a little... (typical msp right?... lol) but anyways same code, not to interject or thread jack Leex but I figure, same issue, recent post and no need to re-post a thread that is already here, and both of us can get a little help, I shouldn't need much just a couple questions answered that I'm curious about, but ill try to help you out as well if i figure out what's going on or whatnot..

so anyways, I just got my car back on the road for the summer last weekend, car ran great, it's set to 8psi right now with the stock supermap (the tune I had was with the exhaust mani leak that I had so I just went back to stock supermap) I think it was last night or the day before that, when I noticed the idle being a little funky and not wanting to stay up, but never died just kinda bogged out a little, the afrs read around 15.7-"--" so really lean, the first time this happened my primary O2 sensor was fried when my coupler popped off the turbo after installing the WR hardpipes with the crappy couplers they come with, the 2nd time was when my hoses going from the oil catch can that came with the WR kit heated and collapsed causing a leak.. now the only thing I can think of. because my idle is fine, it's around 20-25 ish and everything is ziptied with new vac lines all that stuff.. when I got home this weekend I will check and clean the MAF, also the BPV that I had on the hot side of it, the hoses is kinda crimped 1/2 way almost just because of the WR pipe position to the Injen CAI I can try to straighten it out a little but I don't think that should be the issue either.

the only other things I can think of, other than dirty MAF for some reason, would be once before I was looking at the BOV I have and saw the flange or that C clip that holds the HKS BOV on was just a little out of the holding grove, but it was pretty solid, I just popped it back on, but not sure what else it could be... also I am low on gas. or at least 1/4 tank left, that wouldn't effect the fuel pressure would it? (the problem started once I got around 1/4 gas left) could there be something that regulates a/f ratios with different levels of gas? I wouldn't think so but I dono.. this car has crazy things go wrong with it randomly. thanks for the help in advance, I hope it shouldn't take long I don't want to take the help away from leex at all, but don't want to re-post the same exact thread twice

oh and leex, I use to have that same problem last summer, I can't remember what exactly it was, and I think it threw a slightly different code, having to do with a butterfly valve stuck or something like that.. and then again later when I had my exhaust mani leak.. so I would almost bet that it is a vac leak somewhere.. there are so many damn places that it could leak.. I don't know how to do a smoke test but I know that when I Seafoam the car, I can see where any leaks are somewhere... give seafoaming your car a shot through the intake mani hoses going to the PVC valve, might see some smoke come from where it shouldn't

So the problem still exists, high acceleration and dropping into neutral will cause the car to stall. However, if you let it decelerate for 1 to 2 seconds in 3, 4, 5 gear then shift to neutral, the car won't die. Can anyone explain this??? Cleaned MAF already. CEL code P0171 still on. Where else should I look?? I don't want to take it to mechanic's shop, gonna cost 140.00 just for diagnostics. Also, they may not even know what's wrong with the car???!!! I can drive around if I let the decelerate then shift to neutral.

Just checked all the hose today, seems like nothing is lose. I need a professional mechanic's help with these common problems. Don't hear no whistling noise from the engine at all. Everything seems to check out fine. CEL is still on with code P0171. After unplugging an replugging some hose, my friend checked out my OBD2 and it said 2 codes now. P2009 and P0171 ????? intake manifold control something....is short circuit?? Where is that plug or wire? Anyone has pictures? Some guy on another form replugged his VTCS and it worked the CEL went away, however what is a VTCS??? Anyone got pictures of this thing and location??? I am a visual person, pictures would help a lot.

The car also has problems with rough idle in neutral....Anyone know if these is related to the lean P0171 code above??

The lights on the alarm system stays on after I activate it. I don't know why?? Anyone help? Drains the s*** out of my battery, now I just manually lock. They don't turn off until you turn on the car.

Also, my tires weren't original MSP, they are Mitsubishi tires and when I lean left with the steering wheel it would make a scratching sound, sounds like coming from the left front wheel. Doesn't do the same for the right side when I lean right. Any suggestions? Is it bearings? or my axle is not good?

Also, can anyone tell me what the green and white electrical plug on top of the intake manifold are? It's right under the sway bar. I was checking hose's there around that area. Don't know what it is but some air hoses go into it. The green one doesn't suck anything on one of the hose.

Can anyone show me where the EGR valve is on these MSP? So that I may clean? Could this cause the code to trigger?

Can anyone show me a picture of where the idle control valve is ??? Can this cause the code to trigger?

SpeedA...
Do I just spray carb on the manifold where it meets the head? How would I notice a leak? Another weird thing.....

My friend has a MSP too, does the same thing as mine, stall while high accelerating, but his code is P0... something....regarding the 02 sensor. He just doesn't change it and he has a BOV unlike me a BPV.

first, I would tell your friend to buy a new primary O2 sensor, because he can seriously screw up his engine if not blow it up due to lean idle from bad O2 sensor. no good.. he can still stall if he has the BOV only set up venting to atmosphere (vta) but if he's not VTA than he shouldn't be stalling, but the O2 sensor needs to be in good condition and changed

but anyways I was just reading about spraying the carb cleaner, I haven't done that myself, and I think that is mainly for the area near the throttle body and intake manifold, could be for exhaust manifold too, but I most of the exhaust manifold leaks you can hear unlike the intake mani leaks.

first, I would make sure you hook all of those VTCS connections and hoses back up the way they were, here is a pic of mine before I installed the 626 intake manifold and everything is back where it should be, I had that other code with the intake mani last summer, the butterfly thing was stuck open... like I said try the seafoam for the car for leaks, but also it will clean out the crap in the intake manifold and engine in general (search the forums with the search tool to find exactly how to use the seafoam, it's pretty easy) I would also really encourage you to get the boost gauge like they were saying before, it helps out with everything, and it really is a good thing to have for this car, I like the autometer ones, relatively cheap and works great, but ya start with just putting back all of the stock hoses and everything else that has to do with the VTCS, (they are the white and green plugs ontop of the intake manifold) and I would just in general don't pull stuff off like hoses and things, especially if the car is running and without putting them right back where they were to start out with afterwords, just makes things simpler without making them worse. the EGR is on the throttle body, I can't remember exactly where it is, at least not enough to explain it but I don't think that should create this code, can always clean it later or something if nothing else works and if you can take the throttle body off.. I forget what the other thing you asked about (in advanced reply settings thing so can't see what you wrote) but just start small with a few likely simple things without doing anything else and going from there.

pic of IM before install