While I've been driving the XJ the past week after replacing the starter (to ensure it's OK before handing it back to the wife), I've been noticing an acceleration issue. I have no idea how long the car has been doing this since she --the wife, not the car-- hasn't complained.
What I'm finding is that on moderate acceleration -- say 3/4 throttle -- the car will hesitate heavily between 4000-4500 rpm. It will not accelerate past that point, and will upshift at which time everything smooths out. If I drive it 'in anger' and absolutely mat the pedal, it will usually blast right up to near-redline and be perfectly normal. Usually...... Occasionally it will act almost as though it's bouncing off the limiter at 4000-4500, even at WOT.
My thought is the VVT solenoids.. I'm looking for affirmation or pointing in a different direction. I'm kinda planning to replace them anyway, as they are original 115,000-mile parts. When I went through the car in September 2018, I did replace the seals but even though I cleaned up the solenoids, they are pitted with corrosion where they go through the seals and therefore leak oil. I've been putting it off due to the expense -- $225 each for OEM, plus 2 new seals. Now with this acceleration issue I'm thinking it's time...
Thoughts? Am I thinking correctly or should I be looking elsewhere? I should mention that the car got a new fuel pump, filter, and relay, and all new coils 9/2018 while everything else was being done.
I should also mention there is no CEL, and no codes pending or otherwise.
Thanks
-Steve-

 

Most over, I would stick with simpler solutions....could save you that $225.
I might be suspect of a failing knock sensor, it just hasn't thrown a code yet.
TPS would be my next thing to check.
What about plugs, when were they done last?
Check for vacuum leaks, especially on the ends of the rubber lines where they have shrunk away from the vacuum port nipple. Trim the ends and reapply or get new ones....probably need done anyways. I had an intermittent power loss and after cleaning up the ends (especially around the TB), she ran like new.
Check the intake tube for any cracks, mainly the balance tube off the right turn, its known to crack at the neck.
Check the cam cover breather tube to the intake tube for blockage and finally, clean the MAF with a MAF ONLY cleaner, it could be going south.

 

Plugs were done 9/2018 and have 14,000 miles on them. I also just had them all out to address bore wash, and they look good. I replaced both the part-load and full-load breathers (and cleaned the part-load orifice per the TSB) and any vac lines I could find back in June while chasing an evap issue. Also cleaned the MAF (with MAF cleaner) and did a new boot seal where the intake meets the throttle body. Intake tube is good as well.
As I write this, I'm waiting for my wife to go to work and report on how the car feels to her. If she says it feels different than last time she drove it (before the bore wash and starter issue) then I know it's probably something I knocked loose while I was working on it, like maybe a vac line. If she says it feels normal, then I know she's not driving it hard enough to make it act up ☺
I will check both the TPS and knock sensors before investing in VVT solenoids though.
Thanks
-Steve-

 

Sounds like your on it...but I'd be suspect of the MAF. If its going south, it will get worse.

 

I thought I remembered something about fun with the MAF in June while I was fooling with the evap issues so I looked in the file and sure enough I put a new Delphi MAF in it at that time. I wouldn't think it would fail so quickly, but I will keep it on the list of things to check. Wife reported she does not recall it behaving like this before, so I gotta think I bumped something loose while I was removing and replacing the plugs.
Thanks
-Steve-