I've got a 2012 with 114,000 miles on it. No tune. Engine is all original with the exception of the water pump, timing chain, guides etc. etc. all being done when the water pump was done. It surges up and down 200 rpm or so and misses at lower RPM and light throttle and just keeps getting worse. Replaced plugs and it made no difference. Plugs all looked nice when I swapped them out. It started off as a slight shudder which I initially thought was the tranny until it started missing too. No smells, no smoke, mileage hasn't really changed, no CEL. It does seem like it's down on mid-range power too off and on but still pulls hard above 4,000rpm. Not much to go off of I know. Where do I start looking?
Could be wrong but sounds like a small vacuum leak maybe at the BOV diaphragm.
unlikely suspect, but check knock sensor wiring for chafing. do you track data at all? at a minimum, i would use torque pro to log data while driving so that when the event occurs you see SOMEthing happening.
i would clean the IAT and MAP sensors as well with electronics/MAF sensor cleaner. check the intercooler for crud buildup. and turbo piping for pooling oil.
check turbos for damage and loose c-clips.
The shop I brought it to took it for a quick test drive and is trying to tell me it's the transmission. I asked them how that would cause the RPM surging at light loads and missing at idle and they didn't have much of an answer. Tranny shifts and operates fine to me. If they're thinking it's the tranny the symptoms seem more like a torque convertor to me. He's taking it for another test drive with the scan tool hooked up. But they should have done this the first time out IMO. I'll see what he has to say but, regardless, I'm taking it to another shop. I left them a very detailed note about all the symptoms of what's going on and it just rubs me the wrong way that they just take it for a spin around the block and determine it needs a tranny. Man I miss my old mechanic that retired....
UPDATE:
It was the transmission. I had to wait a couple of weeks to get it to the shop that did my water pump a couple of years back. He sent it out to a local reputable place that rebuilds them so I have got my old one back. That took a few weeks. Evidently the pressures were all screwed up at light throttle. He re-flashed or updated??? it when he was diagnosing it and he said it only made it worse but it was getting progressively worse by the time I stopped driving it so maybe that was just a coincidence. The converter was toast also. I've got a 3 year 100,000 mile warranty and all the updates. I pick it up tomorrow.
I still was able to take off from a stop light and go 0-80 under full power like nothing was wrong at all. Ran down the freeway, downshifted fine when passing, could go through the gears with the paddle shifter etc. etc. Weird. My first car had a Powerglide....
Just curious, would the ECM pull fuel/spark from the engine when it senses converter or pressure issues? Is that what I was feeling initially?
do you have a copy of the invoice of work done? was it only torque converter or only pump or ...?
i would think that engine-transmission coordination would make it necessary to pull timing to create the perception of "smooth operation". once outside acceptable parameters, codes should set in the PCM. but IDK 4 sure.
Lubegard Shudder Fixx has been used as a diagnostic in such situations, and indeed by many as an additive to the trans fluid to improve performance/longevity even in the absence of issues.