2001 4.0 manual XJ

It (finally) rained here in Phoenix on Wednesday and I was out playing around running through puddles (not deep, just big splash). I went through one of them and my tires flung a wash up over the hood (35" MTs with cut fenders). Not long after that, I started getting hesitation on acceleration and a P0123 code.

- The vehicle cranks, idles and drives under steady state cruse just fine (no miss or bucking).
- If I slam it WOT in every gear, it does fine.
- If I drive "normally", there's a point in the throttle travel (around 1/4 or 1/3 throttle) that it hesitates and bucks really badly

I've done the following testing:
- Installed a new TPS sensor = no change
- Installed a new MAP sensor (just to be sure) = no change
- Tested the voltage at the TPS (vehicle on and turn throttle shaft while observing voltage change) = 0.8v idle and smooth growth to 4.1v at WOT (both sensors show the same values)

Since both TPS sensors show the same (good) values, I'm starting to suspect the ECU got water in it and shorted something out. The ECU is in the factory location on the driver's side front inner fender and I'm sure it would have gotten "wet" (again, vehicle was not submerged in any way), but I'm surprised water splashing on it would short it out. I don't see it being the coils/a spark issue since cranking, idle, steady state cruise and WOT are all fine. It's just that low throttle transition (there must be a transition point in the fuel/air table) that has issues and again, if I just slam WOT in every gear, no hesitation (because I pass the "dead spot" in the table).

Any guidance on what to try next? Buying a $250 ECU is going to hurt if that's not the problem.

Thanks,
Chris

 

Did you check the spark plug boots at the plugs and coils ? if water got in there it could be your problem .

 

I hadn't gotten to that yet (01 is the coil rail so takes a bit to get it off). Oddly enough, the hesitation is gone now. I'm still getting the code but it's running fine. Perhaps whatever got wet dried out?

 

Did you clean the "connector" for the throttle position sensor? I use a spray can of electrical contact cleaner. You mentioned you replaced the TPS, but the connector could still be wet.