Very reasonable. I just had my intake manifold off to change plugs and gaskets and when I flipped the intake oil poured out. I would suspect if you were sucking in oil like I was that could muck up the inside of your cylinders.

 

I was sitting in the parking lot at work and it sputtered or missed and the RPM's jumped about 250, not 2500, and I gave it gas and let it idle and it continued to do it about 4 times. It would sputter like a misfire at idle and jump up 250 each time from about 750 to 1000 RPM's. I don't know what that's about. Still no indicator lights or fault codes........frustrating.

 

Sounds like it's in enough trouble that it struggles to keep it running so may have no time to flag codes. Go troubleshooting (or take it somewhere).

 

It doesn't struggle to stay running or anything, in fact it idles pretty nicely at 750 and always has. I've never had it try to stall on me or anything at any point. It's always just started up and idled normal. This new development, I think, is a result of my overall issue with it misfiring on a grade or uphill. Yesterday in the parking lot it was like there was an extra combustion in the chamber that made the RPM's pop up slightly. Kind of a jolt like pressure build up that released and it did it like 4 or 5 times consecutively with maybe a 5-10 sec delay in between each. I just need to take it to a buddies house or somewhere where I have a garage and can dig into the engine. I'll have to just start replacing things until there is nothing to replace, except what I've already replaced.

 

Hi - this is just kind of a swag but ... have you had the fuel pressure checked? This almost sounds like a low fuel pressure symptom that I experienced in another (non-Jag) car.

Also - have you changed your fuel filter?

This is all assuming that it's not actually connected to your recent tune up work.

 

Fuel Filter was replaced when I did the tune up, so I wasn't figuring it to be a cause of anything. Although if it's faulty it's worth another look. Fuel Pressure is stable across 5 drives of 10 min or longer and 2 freeway drives at 55.22PSI. The lowest recorded was 55.10PSI and the highest was 55.34PSI. I honestly don't know if that is low, average, or high fuel pressure.

 

I should add that it's never recorded Pressure below 53psi or above 60psi on any of my data logs and 55psi was recorded the most frequently.

 

I've been tracking my OBD2 data by exporting it to an excel sheet. It list all of the readings per second and I added a column for minutes too. I realize, now that I've got the data and averages, this forum doesn't support Excel attachments....... Any way to incorporate that? If not I'll have to reformat my data into averages over an overall drive period (i.e. 20min drive, 45min drive) for those that are still curious.

In addition to this update, I have a question. As I'm troubleshooting and driving around waiting for a code, my car started consistently acting up yesterday and today. It has been mid 80's to 90's here the last few days. One thing I've been tossing around is that it could be O2 sensors. Since my car was sputtering/misfiring today pretty consistently, and always when I went uphill, I was tracking the data to analyze. I read up on normal O2 reading and I learned that readings will range from minimum 0.1v to a maximum 0.9v. If the O2 sensors are operating as balanced, or at the equilibrium point, they should register 0.45v.

So i got curious and started looking at my O2 readings. What I discovered is:
50% of the time my O2 reading average 0.721v BK1 & 0.698v BK2 (high)
30% of the time my O2 reading average 0.477v BK1 & 0.478v BK2 (ideal)
20% of the time my O2 reading average 0.206v BK1 & 0.208v BK2 (low)

I noticed 2 instances on both banks of readings at 0.09v, under the minimum 0.1v, and a dozen or so instances of reading at 0.8v or higher, but below 0.9v maximum. Probably why I'm not getting any codes or MIL lights. Does this all look normal to those of you reading this or keeping track of this thread, or does that mean pretty definitively that my fix might be the O2 sensors considering I'm nearing 100K and I just had the plugs replaced?

 

O2s or coils are the most likely. Have you changed the coils?

 

Pre-cat (Sensor 1) O2 sensors should fluctuate. The engine constantly goes from rich to lean and vice versa to keep the air/fuel at stoich. This happens fairly rapidly. Post-cat (sensor2) O2 sensors should remain fairly steady (if your cats are working properly). Your post-cat O2 sensors will follow the pre-cat sensors if the cats are bad. Pre-cat should read 80mV-900mV, rapidly changing. Post-cat around 600-700mV, fairly steady. This is coming from a service tech. This they would consider "normal". You want to watch the highs and lows for sensor 1, use a graph if you can. If the graph looks flat, you may have a bad/dirty O2 sensor.