Engine sputtering at idle and low RPM

[Boilermaker19]

So the last few days, my MSP has started sputtering at idle. It doesn't do it all the time, it will idle fine for a while, then it starts dying, chugs a bit, then will suddenly roar to life on its own. Also happens at low RPM. once I'm above 2000, everything seems fine. This is especially problematic given the iciness of the roads. The only CELs I have are O2 sensor-related, and have been there since I bought the car, and probably have more to do with the lack of a Cat than anything else. I would think IACV, but that should throw a code. When I monitored O2 sensor voltages, they were not erratic. The "absolute throttle position" reading on my OBDii analysis software, however, is at 10% when I'm not touching the throttle. Shouldn't it be 0%? I pulled three of the plugs (ran out of time), and they looked okay, just a little white powdery, possibly running lean, i guess. I am planning on Seafoam and plug change this weekend, but the erraticness makes me think that it's not just dirty injectors. I'm running FMIC with a BOV, SSAFC running the winter FMIC tune from here, and a 3 inch catless exhaust, forged internals and 9 pounds boost.

 

[Boilermaker19]

Update: I seafoamed her tonight, then replaced the spark plugs with properly-gapped ones per this forum, and the problem has gotten worse. any time the rpms drop below 2000, she sputters and dies.

 

[Schwamm]

The first thing I would do is check for a vacuum leak. My car has behaved like that many times when a vacuum hose pops off or springs a leak.

 

[Preferio]

So the last few days, my MSP has started sputtering at idle. It doesn't do it all the time, it will idle fine for a while, then it starts dying, chugs a bit, then will suddenly roar to life on its own. Also happens at low RPM. once I'm above 2000, everything seems fine. This is especially problematic given the iciness of the roads. The only CELs I have are O2 sensor-related, and have been there since I bought the car, and probably have more to do with the lack of a Cat than anything else. I would think IACV, but that should throw a code. When I monitored O2 sensor voltages, they were not erratic. The "absolute throttle position" reading on my OBDii analysis software, however, is at 10% when I'm not touching the throttle. Shouldn't it be 0%? I pulled three of the plugs (ran out of time), and they looked okay, just a little white powdery, possibly running lean, i guess. I am planning on Seafoam and plug change this weekend, but the erraticness makes me think that it's not just dirty injectors. I'm running FMIC with a BOV, SSAFC running the winter FMIC tune from here, and a 3 inch catless exhaust, forged internals and 9 pounds boost.

Nope, 10% is completely within acceptable limits. It can't be closed 100%/open 0%.

What DTC's do you have?

Pending or current?

What does the STFT and LTFT look like?

How many grams/min is your MAF reading?

 

[Boilermaker19]

Stored codes are P0140 O2 sensor no activity detected bank 1 sensor 2, and P0037 Ho2S Heater control circuit Low Bank 1 Sensor 2. There was a pending Cylinder 3 misfire detected, but not until after the seafoam, so probably from that. If I recall correctly, my STFT was -25 when I was monitoring it as it was dying last night, but I was not logging at the time. I'll have to log the MAF.

 

[Boilermaker19]

Also, when I seafoamed I noticed an exhaust leak, probably from the S pipe.

 

[Preferio]

Also, when I seafoamed I noticed an exhaust leak, probably from the S pipe.

Post LAMBDA sensor leak, effectively negligible. At least in regards to your concern. The downstream is catalyst monitoring and in no way will cause any drivability concerns.

Your STFT are through the roof, man. It's running lean and trying to throw fuel at it to correct it. It's pointing towards a post MAF leak. Smoke test it.

 

[Preferio]

Wait, you said -25... Meaning the exact opposite..

Edit: You're over-fueling. I'd look at my upstream O2 data and reload the AFC with a different tune.

Edit: Still check your MAF.

 

[Boilermaker19]

I was thinking that I might load a new tune and see what that does for me, also thinking I'll pull the O2 sensors and clean as necessary. Gonna do that when I get home from work. I hate it when I have to borrow my son's Miata to get to work.

 

[Natey]

Do you have boost issues too? Stock turbo?

If so, check the wastegate and it's actuator.

 

[Boilermaker19]

Not having any boost problems. I do have the stock turbo, but not the stock wastegate. I wouldn't think it would be turbo-related since the problem is at idle and low rpm when the turbo is not doing anything.

 

[Natey]

It was for me, but I also had intermittent turbo weirdness. Sometimes it would fall flat on its face, and sometimes it would take off like a rocket. It always died at stop signs though. Once I swapped out the WGA the car runs like it should.

I'm glad i didn't damage anything, because I was definitely over boosting sometimes.

 

[Boilermaker19]

Well, I cleaned the O2 sensors and loaded a new map, no dice. . The engine is definitely overcompensating for something. When you start it cold, it will run for a while, then when the IACV is warmed up enough to let the idle drop, the car sputters and dies.

 

[BOOSTR]

What is your vac showing both before and when enters into that sputter and die mode? Like others have indicated I suspect a vac leak somewhere.

 

[Boilermaker19]

I'll watch the vacuum on lunch. Another internet search has got me thinking EGR valve, so I'm gonna clean that on lunch as well. Also, last night I discovered the pictured mess, which is the downstream O2 sensor connector. Not sure if that could be a cause. I taped it up really well when I put it back together, and all of the connections seem to be made. Is there anything in this collector that could be heat damaged, aside from the connectors?
Having trouble getting the picture to load from Flickr for some reason. Trust me, it's fairly melty.

 

[BOOSTR]

Your 2nd 02 does nothing to impact or alter driveability. That's not the cause of your RPM issue.

 

[Boilermaker19]

Vacuum is around 20, no problem there. I couldn't get the EGR off at lunch, but I squirted the hell out of the IACV, and loaded another new map, and for the time being, no idle issue. Time will tell.

 

[Boilermaker19]

It's still doing it, just not as badly. Sometimes, in fact, it will idle rhythmically, the rpm's rising and falling. It's not quite dying, but i frequently give it a little gas at a light to keep it from dying.

 

[hornsfan10609]

20 is low vacuum, it should be 22-24 at least. When was the last time you replaced the ignition system?

 

[Boilermaker19]

By ignition system do you mean the coils? I replaced the plugs last week. I've only had the car since September, and I don't know how long ago the coils were replaced. I thought I had this licked, found a vacuum leak associated with the tubing going to my SSAFC, but this morning the problem is back with that plugged off.