Rough Idle Fuel Trims Part Load Pegged Rich

Dominic Owner/Technician Massachusetts Posted   Latest   Edited   Bounty  
Resolved
Driveability
2014 Volkswagen Jetta S 2.0L (CBPA) 6-spd (09G) — 3VW2K7AJ6EM210381
P2178 — System Too Rich Off Idle Bank 1
P2187 — System Too Lean at Idle Bank 1
P0506 — Idle Control System RPM - Lower Than Expected
Stalling
Running Rough

Car brought in for stalling idling rough, hesitation. Found B1S1 code- replaced resolved code and light but extremely rich condition still exists, Car is maxed out at -25% multiplicative and about -3% additive. In freeze frame data the codes set at 82% load. Now this is CBP motor is map sensor controlled, Baro readings match map sensor at 980mBar engine off. The odd thing to me is that this car is reading Multiplicative fuel trims at idle rather than driving at part throttle. The multi readings went from 0 after a code clear to -25% sitting there idling. 

It sat and ran pretty ok for a new minutes and the engine load calculated around 22%, all of a sudden the car starts idling rough, calculated load starts climbing and the baro reading starts climbing from around 450 to 980 and then stalls, i pulled the intake boot to see what is happening at the throttle body when this occurs and found that the throttle blade is opening up wide open and hence the map sensor reads baro pressure. RPMS do not increase as the blade opens and the injectors PW do not increase. 

To me the car thinks it is driving down the road with a load and its acting crazy thinking theres a load, where does the load calculation come from? unplugging the MAP sensor made no change, unplugged the map sensor defaulted to 1200 or so and it didnt change the stalling or rough running or the fuel trims.

I read the post with comments about coils, plugs, wires, all are genuine on this car, does the coil have a bearing on the calculated load based on KV?

None of the data, temps, etc looks off. 

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Jim Owner/Technician
North Carolina
Jim Default
 

If this has a high pressure fuel pump, check the oil and see if it smells like gas, possible HP fuel pump leaking into crankcase/ breather system.

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Dominic Owner/Technician
Massachusetts
Dominic Default
 

It doesn’t - it’s old school , fuel filter 4.0 bar replaced

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Richard Technician
New York
Richard Default
 

I don't believe the coil has any effect on the calculated load. I think that as the vehicle is running rough the PCM is opening the throttle to keep the RPM's up and so the MAP voltage is dropping, so the load is increasing. I would scope the secondary on that vehicle to see if the kv's are low. I have seen a few of these that threw me a curve and got me running in circles when a set of ignition…

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Hans Technician
Utah
Hans Default
   

I just checked and it's a 2​.​slow My other post was about fsi engines. I'd almost start with a capacitive discharge of the system and see if that wakes it back up.

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Dominic Owner/Technician
Massachusetts
Dominic Default
 

Hans thanks I did see your offerings. There is one other 2.0 post that’s similiar but not conclusive.

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Louie Technician
New York
Louie Default
 

Hi domenic this Jetta is exhibiting the EXACT same symptoms of a faulty mass air flow sensor​.​Are you sure there isn’t one tucked in the air cleaner somewhere?

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Dominic Owner/Technician
Massachusetts
Dominic Default
 

Louie thank you, I’ve fixed many older vw MAF issues but this cbp is the old relic 2.0 they resurrected except made it a map sensor car…

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Randy Diagnostician
Colorado
Randy Default
 

Any chance you can post scan data? Enhanced and/or generic? Your description is odd and doesn't make sense but based off what I think you are describing, the load is real and the ECM is trying to open the throttle plates to maintain RPM. Last time I had one like that the AC compressor was locking up. Are you sure it's not setting any DTCs after stalling? Pending? Resolved code or codes?

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Dominic Owner/Technician
Massachusetts
Dominic Default
 

i did post codes above- see the p2187 p2178 and the p0506, those codes are pertinent, if i post a scan it will show other random codes relating to unplugging injectors etc.. I understand that the description is odd… its a VW with a non typical for VW fuel management system with a MAP sensor. I can clear and start over with fault codes, after it acts up again, I also have to scope the ignition…

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Randy Diagnostician
Colorado
Randy Default
 

I would concentrate on the P0506 as it seems to be the reason your throttle plates are opening and load is increasing. Ignition break down is plausible. Check the basics. Sorry, that's all I got with the data posted.

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Randy Diagnostician
Colorado
Randy Default
 

I have and use the VCDS so I know it's advantages and disadvantages. What I would do is switch to a different tool and graph generic data during the stall and post it. Make sure you include EQ ratio for B1S1 and rear O2 voltage along with STFT, secondary LTFT, commanded & relative throttle position, ABS and Calculated load, RPM. Your video indicates RPM is dropping and the throttle plates…

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Dominic Owner/Technician
Massachusetts
Dominic Default
 

I posted a screen of the iscan in generic with selected data . specifically noted is that the car is running badly in open loop already but the minute it goes closed loop it stalls. On this video it switched in and out for a few before stalling but in previous attempts it immediately stalled when it went into closed loop. AC is turned off. completely btw

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Randy Diagnostician
Colorado
Randy Default
 

Did you reset fuel trim adaptives after your B1S1 repair? without STFT and the without the rear o2 up to temperature I can't be sure but it looks like it is taking too much fuel away and stalling the engine but EQ is reflecting that so the only way this could happen is if adaptives have not been reset. If B1S1 is correct, you are idling ok at 5% rich and then in closed loop it goes to something…

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Dominic Owner/Technician
Massachusetts
Dominic Default
   

I did reset adaptations (learned values) and did capacitor discharge. No change im uncertain what the pid shown is here for brake booster pressure in mbar. The booster hose also has a map sensor built in to it, it always reads zero that I see. Further to the other posters response I am used to the baro pressure being measured in the ecm but all other vw I have worked on, and it’s many have had…

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Dominic Owner/Technician
Massachusetts
Dominic Default
 

Disregard the booster zero mbar, comparing another mk6 but a 2.5 that pid is also zero. Generally on the similar but 2.5 car the baro reading is 980 and the altitude correction is 3.1 but the running map pressure is 290-300 at idle and the calculated load is around 17% or so

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Timothy Technician
Illinois
Timothy Default
 

Baro is likely calculated in the ecm. Im going to try and see I can get into the factory side for you to see if there is any concrete proof on this. Vw and audi have been using the pcm as a baro sensor as well for a long time. They call it altitude correction factor. You calculated load is changing because your baro is going nuts. As long as powers and grounds are good to the ecm it appears it…

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Dominic Owner/Technician
Massachusetts
Dominic Default
 

I think baro is read by the map koeo but not confirmed. The altitude correction factor pid staus around 3% that I’ve seen. It doesn’t fluctuate

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Bill Owner/Technician
Michigan
Bill Default
 

Dominic do you have a way to test the fuel? It would be nice to rule that out if possible. This is often overlooked but obviously very important.

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John Owner/Technician
Massachusetts
John Default
 

Sounds like engine cannot breath? Exhaust back pressure?

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Dominic Owner/Technician
Massachusetts
Dominic Update
 

I am out of the country until Monday and will be looking at this again on Tuesday , will post an update then thanks

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Tom Engineer
California
Tom Default
 

Hi Dominic, any update?

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Dominic Owner/Technician
Massachusetts
Dominic Resolution
 

Hi Tom and all- yes the update is that a used Donor ECM fixed it, nothing genius about it other than try known good unit. Nothing was making sense in the symptoms and data. Anyways, its all all set and out on the road. Thanks all.

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