1993 LS-400 150K miles
If I accelerate smoothly, no problem. If I need to accelerate more quickly, i.e. to pass or just to move out more quickly, the engine sputters. The RPMs drop 500 and then pop back up a little, but then drop back down (1 second cycle). If I hold the pedal there the engine keeps sputtering, trapped in the cycle.
If I let off the pedal the acceleration evens out. It's as if there is a line and if I cross it too quickly, it sputters. If I stay smooth and steady there is no problem.
Work done so far: Throttle position sensor replaced, throttle body cleaned, plugs replaced, and fuel filter replaced.
The dealer looked at it and said that they have had a few cars with this problem and replacing the computer ($1100) usually works, but he didn't sound too confident.
Suggestions?
Thanks.

sounds like a fuel air ratio problem do you know if it is getting sufficient fuel delivery ? although i don't know how you would check that.
I don't know if the fuel pump is constant output but i would assume it is could it possibly be that the fuel pump isn't delivering enough and when you open the throttle the pump doesn't pick up fast enough

Bet some of the more serious modders will have a better idea as they play with fuel delivery and the like

Had a problem like this on a 3.0 supra, turned out to be worn out spark plugs, maybe an idea to take a couple out and see if they are burnt .

I have this problem, albeit slight and intermittent, at exactly 45 m.p.h., normally when the engine is just warming up.
I've changed the plugs, leads, cleaned the TB yet it still does it, sometimes accompanied by a sulphuric smell from the catalytic convertors. Fuel and air filters are new, too. I'm about to change the trans fluid as my next step.
The guy at my independent Lexus garage has witnessed the fault but has not been able to diagnose it as yet. Possibly a temp. sensor, he reckons.
So please keep us posted should you make any progress on this one!
Thanks,
Rich

ive had the same problem on and off for about 18 months sometimes its worse than others.When it start to play up i put a tank or 2 of super unleaded though and im not 100% sure but i think this helps,ive posted on this topic before and someone did say it might be a trans problem ive since had the oil changed ,also ive tried fuel additives i think that if my memory is ok that is what might have sorted the problem when it was at its worst.One more point thats not relivent to the others with the problem is my car runs LPG 90% of the time.
Andy