93 240 LH2.4 hesitation, knock, poor mileage

[aimlessone]

Hey All,
I'm running out of ideas for troubleshooting a throttle-on hesitation, poor fuel economy, and ignition knock under heavy load on my 93 240 LH 2.4. Any help or tips would be greatly appreciated!

A bit of context:
This problem started suddenly while running errands. I had gotten gas, driven to another store (the car ran fine), got out of the store, then restarted the car at which point is was running like it had a miss. It eventually smoothed out after a couple minutes idling in the parking lot, but then would hesitate when pressing on the throttle from a stop. The problem persisted, then slowly stopped happening over the next week or so.

I also started to notice a knock under heavy load that would get worse on longer (>20 minute) trips and that my fuel economy dropped substantially. These problems did not go away over time.

I disconnected the battery to work on something unrelated. After reconnecting the battery and restarting the engine had a surging idle and I'd have to ride the throttle to keep it from dying. After several starts and driving it briefly (1 block or so), the idle smoothed out and remained smooth on subsequent starts, even if the engine had cooled off completely. The knock and bad fuel economy persisted. I'm assuming this is related to the ECU resetting after losing power, but something is still wrong.

What I've tried, with no change in behavior:
-Replaced the knock sensor
-Cleaned the throttle body
-Replaced the fuel pressure regulator (it was leaking some gas through the vacuum line to the intake)
-Replaced every vacuum line I could find (many were loose/cracked)
-Replaced flame trap (it was oily, but not clogged)
-Adjusted and checked the function of the throttle switch. It had continuity to ground with throttle off, and about 2.2kohms resistance when pressing the throttle
-Checked MAF/AMM with ohm meter (it's right around 3 ohms)

Other recent-ish repairs
-Injectors had been changed about 5 months ago
-Replaced timing belt in April 2020
-New plugs, wires, cap, and rotor about 5 months ago

Is there anything I'm missing? Thanks for your time!

[gnalan]

Could be a bad tank of gas, possibly contaminated with water. It's been known to happen at certain gas stations that use ethanol in their gasoline.

[volvolugnut]

Try to drain and replace all fuel - it may be contaminated.
Check the ignition basic timing - it may be off.
Check vacuum hose to the ignition controller near the coolant tank. Test with a hand vacuum pump to see if a leak has developed.
These suggestions are based on earlier year 240s and may not apply to 1993 model.
Sorry for the late reply - I did not see this post until today. They are not a lot of 240 people at MVS.
volvolugnut