1997 LS400 won't accelerate when accelerator is pressed.
 

I have a 1997 LS400 that had a swapped engine 1.5 years ago. The ECM won't store any error code (i.e all error codes will be erased after engine shutdown). It never ran very smoothly since the engine swap, nevertheless it still accelerates. Recently it started developing the following symptoms: Sometimes it never goes over 40mph even though you press the accelerator to the floor. It doesn't have power to climb slope road. I had to pump the accelerator to get the car accelerate. It idles fine, But when parked, the engine rpm goes to 2000 and then drops below 2000 when the accelerator is pressed, also there is a popping sound accompanying the rpm drop. On two occasions, the check engine light flashed on the road. At one time, the error codes were P0171 and P0306. On another occasion, the error codes were P0171 & P0306. Right now there is no error code. Anyone has any thoughts on what's causing this kind of behavior? Thanks in advance.

Sounds like a fuel supply problem to me. I'd try to bypass the fuel pump resistor to confirm it.

X2,

And check fuel pressure and change fuel filter etc.

Thank you both for the prompt responses. FYI, the fuel pump was replaced last year.

Was the fuel filter replaced at that time?

No, Sir. I thought the filter was inside the pump. Is there an filter outside the pump?

I just did mine on my 97 LS...it's above the differential towards the right side. Make sure you have line wrenches to remove it otherwise you'll be replacing entire fuel lines.

Mine had 280k and I wasn't experiencing any issues but I did it because of age and mileage.

Cost was $35 at the dealer...they had the exact same part number and it comes with a bracket for mounting.

Thank you for the info, Losiracer2. I will replace the filter.

The engine revs to 2000 when in park without touching the accelerator?

No, the engine won't go over 2000rpm even the accelerator is pressed. In fact, the rpm dropped when the accelerator is pressed.

Wont hold any codes, sounds like notorious ECM problems.

Yes, it absolutely smells of ECM failure. I've never seen a fuel filter cause the ECM to erase codes after shutdown so I would venture to say that changing the fuel filter won't do jack except waste time and money.

I had the same problem on my 97 & it was the fuel pump. If yours was replaced & assuming it hasn't gone bad then it has to be the fuel filter. You can also check the fuel pressure but the 97 doesn't have a test point for you to hookup the fuel pressure gauge so if you want to go that route, you will need to disconnect the hard fuel line's connector in the engine compartment on the driver side, right next to the strut tower & insert a T adapter there. The problem could also be the ECU. Have you replaced all the capacitors in the ECU w/ new & correct ones?

Hello Superfast1 & all, Yes I did replace all the capacitors. In addition there was a trace breakage due to corrosion from the capacitor fluid and caused P1600 error. I repaired the trace and the P1600 was gone. I am not 100% confident with the ECU/ECM even though that the Caps have been replaced and the trace was fixed. Since its a 97 I can't just plug/play with another ECM. I wish there was a way to just by pass the security chip:)

Basics first, did you do what I said.