I'm stuck... I've thoroughly searched the web, but am now out of solutions to attempt to solve this issue of stuttering acceleration. This problem randomly showed up (no noticeable correlation to changes made) and it happens at all speeds, but does seem more prevalent during lighter acceleration (versus when I floor it).

I can only think of three more items to attempt, but if any of the three were bad, wouldn't they reflect in my fuel trims (which seem OK and are attached below)?

Remaining possible items?

1. Catalytic converters (I've been unable to get my 'Catalyst' ECU check readiness test to complete, could it be correlated?)
2. Purge valve (front only? Or front and rear valves?)
3. O2 sensors (just replaced last year, but maybe bad again?)

Items addressed after the stuttering issue became present:

• EVAP - Vacuum leaks repaired (confirmed with smoke tests)
• Fuel Pressure - Full pressure tested
• Throttle body - Cleaned
• Injectors - Cleaned
• Coils - Tested with old and new set
• Transmission (Torque converter) - Oil changed (resolved rough shifts and grind/rumble noise, but not the stuttering)

Related items that were successfully repaired prior to the stuttering issue:

• MAF - Replaced (resolved CEL codes)
• Fuel Pressure - Pump & filter replaced
• O2 Sensors - Replaced all four sensors (resolved CEL codes)
• Coils - Replaced (resolved misfire & CEL codes)
• ECU - Tested by shop

@ Idle (top is long term, bottom is short term)


@2,500 RPM (top is long term, bottom is short term)

 

Despite the changed coils, sounds like a coil breaking down.

 

I'm assuming that would mean the stuttering is caused from intermittent misfires due to inconsistent sparking at higher RPMs?

This could make sense because I was only able to test each coil (with it's correlating plug) individually by turning over the engine with the fuel pump disabled. Though, it's still odd to have the same issue with two full sets of coils (OEM for the first set, cheaper aftermarket for the second).

 

Check your thermostat, could be stuck open causing the car to run rich.
Happened to my 96 XJR.

 

My experience with engine stuttering or stalling when warm was always the Crankshaft Position Sensor (CKPS). A failed or failing CKPS would not throw a code. If you have replaced the CKPS and tried every thing else but the problem still persists, the next suspect is the ECU which may have been compromised by water ingress.

 

I really appreciate the suggestions, but unfortunately the problem is still persisting.

I still have no CEL codes, but in my system monitoring (SMOG) I've NOT been able to complete "Catalyst" test, and the "Oxygen Sensor" test has been very difficult. Could there be any correlation?

Since my last post, I've replaced/have completed the following:

• Engine coolant thermostat
• Crankshaft position sensor
• Vapor canister purge valve
• Cataclean
• Smoke test (again)
• Back pressure test (very small leak from each side's pipe extensions that connect after the CATs)

 

check the throttle position sensor.

 

For each unset OBD monitor a whole bunch of codes cannot flag, which can make progress tougher.

 

You have changed coils (and lots of other parts) but not spark plugs????

 

I tested the TPS with a multi meter when I cleaned the throttle body, and it seems to be fine. Then again, I can only test it while stationary, and I don't feel this stutter problem unless the engine is under load.


I should have clarified better- Yes, I did the plugs long before the coils. I also tested each combination of old/new plugs/coils, and multiple brands of plugs.