Shudder and hesitation under load sounds like a fundamentally different problem than surging idle. Is this a V8 or V6? How many miles? Does it shudder only when moving, or also when under load out of gear (higher rpms) or maybe when in gear and loading against the brakes (brake torquing)?

Fuel/air mixture problems that get worse under load generally point to a fuel delivery issue. If your air intake gaskets are leaking, you should notice it more at idle, less under load (at idle you would see high positive fuel trim, and at higher RPM the fuel trims would drop - same as any vacuum leak). I guess the one caveat to that is, on the supercharged car, you could start losing boost under load as well, but I would still expect to see high fuel trims at idle. So, unless you are seeing high fuel trims at idle, replacing the air intake gaskets would not be high on my list of things to try.

The fuel pumps or fuel rail pressure sensor could be failing. If it’s affecting both sides of the engine, that would point to the low pressure fuel pump in the tank (known issue). If its affecting only one rail, that would point to one of the hp fuel pumps. You could start by taking a look at fuel rail pressure on the GAP tool.

A fuel injector could be clogged - thinking cylinder 5 here. If you have the V8, you could try looking at the pulse width modulation using the GAP tool to see if any of them are much different than the others. Sadly, this function does not seem to be available on the V6.

Could also be a spark issue - plugs or coil pack - again thinking about cylinder 5 misfire.

I wonder if it might not be the engine, but something in the drive train causing the shudder. Thinking right now about the torque converter. Torque converter issues are often due to low/old transmission fluid and can be improved with a fluid change, though not always.

 

It's a 2012 V8 (Non-SC), 190K. I rebuilt the engine 50K miles /2yrs ago, and at the time replaced just about everything- including the HP fuel pumps and pump in tank, but not the fuel pressure sensors. The injectors I had tested & reconditioned, also replaced all fluids including transmission fluid. This thread has made me appreciate how sensitive the fuel delivery system is, but at same time I don't want to deviate from the subject and if it be necessary to start a new thread I'm for it.
I'm not too familiar with interpreting and analyzing the long/short term trims over time. Any advice on which values to focus primarily on? Some values , such as the desired fuel pressure readings, fluctuate intermittently from 0 KPa to 10K. Not sure if that's normal. During idle, my readings are as follows:

 

Interesting - is this a rebuild you did yourself, or had it done at a shop?

For fuel trim, just pick “Long Term Fuel Trim Bank 1” “Long Term Fuel Trim Bank 2” “Short Term Fuel Trim Bank 1” “Short Term Fuel Trim Bank 2.” They give fuel trim in percent. I find it the easiest to use. Add them together at any given reading to get total fuel trim. Positive trims indicate the engine is correcting for lean conditions, negative is trimming out a rich condition. Looks like you are running rich in bank 1. If I remember correctly, the V8 uses odd/even numbering for the cylinders, which puts cylinder 5 in bank 1. My mind immediately jumps to a leaking injector. Increasing fuel rail pressure under load might cause it to leak more under load than at idle and cause the cylinder to start missing. When replaced, you’re supposed to use a new seal kit, but even then, they can leak sometimes. Check the fuel rail connections for leaks too - I’ve seen one or two reports of a junction leaking just enough to lose pressure. Any black smoke at startup? Sometimes a leaking injector will continue leaking when the engine is shut off and give some black smoke on startup.

I’m not sure what is going on with the desired fuel rail pressure. I don’t think that should ever be zero. When I’ve looked at fuel rail pressures in the past, I run the desired and the actual and compare them to see that they are close. Never seen a zero value. But desired pressure is a calculated reading of some kind, not a sensor reading. The actual fuel rail pressure is the sensor reading. So, not sure what’s going on there. I guess it could still be a sensor issue of some kind (the fuel rail sensor failure has been frequently reported in other forums), or maybe a glitch in the gap tool connection (I had this happen once - readings would just freeze - had to tighten up all the obd pin slots in the port).

As for the other readings, pulse width on the injectors is only useful (at least to me) if you look at all of them at once so you can see differences. o2 sensors need to be read over time - at idle they should go up in down in a wave form. Since you just replaced them not long ago, I doubt there is anything wrong there.

 

The purge valve opens roughly 10 minutes after the engine has started and does indeed operate most of the time, continuously. I do not have surging idle, I have decreasing idle by 100-150 RPM (550-500 instead of 630/640). If I disconnect the line from the purge to the tank while the purge is open, the idle stays normal and does not drop, but the purge continues to tick, louder of course. As soon as I reconnect, the idle drops. This ONLY happens when fueling and lasts for approx 20 minutes then goes away.

The canister's relatively inexpensive. I dropped the full spare but could not see any easy way to remove it. Couldn't find anything in the workshop guide either. Might be worth paying the dealer to do it.

 

When I say surging idle, I’m not distinguishing between surging up or surging down - just a rhythmic change in idle. I think that’s what you’re experiencing, right? So, turn off engine, fuel up, cap back on, start car, and the engine starts having this rhythmic drop in idle for about 20 min. If you disconnect the purge during this period, the idle evens out. Is that correct?

Sounds like liquid fuel getting into the canister. The car is supposed to adjust the air/fuel mixture to compensate for a normal amount of fumes, but it probably cannot compensate enough for the richness of the vapors in the canister. I don’t know why it stops after 20 min (maybe purge is closing?) and doesn’t return until the next fill up.

 

Rebuild was done at home, made a time lapse vid The injector seals were replaced but it does make sense that be a possibility of a leaking injector. There is no black smoke at startup. Will do some research on viable compression tests on this vehicle, which could point to a leak in Cyl 5. My fuel consumption has been higher than normal and I'm leaning on changing the front O2 sensors which were Not replaced- just the MAF were replaced. While I had the air manifold out, I noticed excess carbon buildup on some cylinders more so than others. Cyl 5 had buildup which surprised me of how much accumulation occurred in such short time. I suppose excess carbon buildup on the intake ports is one of the disadvantages of the direct injection engines. Should I reset the fuel parameters using the GAP tool?

 

The canister should be relatively easily to access, but having it done standing at a shop vs on your back makes a big difference.

 

Great video. I recognize “Redtop Engines” - maybe from landroverworld.org? Anyway, these engines tend to pull a lot of oil through the PCV and into the air intake, and I think that contributes to the carbon buildup (in addition to being direct injection). I have the SCV6, but I think the V8 does it as well. The oil separator that’s built into the valve cover just doesn’t seem to be adequate. On my engine, the two rearmost cylinders had a lot more buildup on the intake valves than the other cylinders. I assume the oily air from the PCV just takes a flow line to the rear cylinders for whatever reason in the SCV6. Not sure if a similar effect could be contributing to the buildup in your motor.

I’ve never reset the engine adaptations. I doubt it would do much good, but probably wouldn’t do any harm either. As I understand it, the engine will run rough for a bit after resetting until it sets new adaptations. I just hate messing around with the computers - always afraid I’m going to brick something. I figure once the mechanical issue is sorted, the computer will adapt new values anyway.

 

Yes, we're on the same page. I'm finding 2 different part numbers for the canister with the same application but very different prices, LR013715 and LR013720 - any idea which is correct?

 

I don’t know, but I notice in the description that part number LR013720 says “incl. vapor canister purge solenoid.” Oddly, that seems to be the cheaper part. I think you’ll have to call the parts counter on this one - hopefully they can figure it out. Or, if you are close to a dealer, see if they’ll let you order both for pickup and then just not take (return) the one that doesn’t look right.