92 Ls400 Hesitates At 2100rpm

[92LS400...s/c?]

recently my LS has been hesitating at 2100RPM usually when I'm going around 60-70MPH, and i don't know why its doing it. I just replaced my water pump about a month ago and the car has been hesitating since. So i replaced my plugs with platinum plugs and replaced the plug wires, pcv valve and cleaned the throttle body i also got a new air filter. None of these things have fixed the hesitation, does anyone have any ideas what it could be?

[92LS400...s/c?]

no guesses, anyone?

[kenmac]

Have a check and clean your MAF sensor connector.

[slicclex]

I have the same problem you have. I replaced the whole MAF unit, spark plug and wires, crankshaft sensor, and cleaned the TB. Nothing seemed to solve it. I don't know if anyone can figure this problem out, not even the Lexus dealers could figure this out.

[92LS400...s/c?]

well i just changed the fuel filter and it fixed it quite a bit, it still has a slight hesitation but not half as bad as before, next im gonna try the injectors and see if that works.

you might want to try that too slicclex

[slicclex]

Yeah I replaced my fuel injectors too but haven't changed the fuel filter yet. Do you install the fuel filter yourself?

[92LS400...s/c?]

yeah i do everything myself, it wasnt that hard but make sure your on empty before you do it. i didnt and ended up waisting like 10 gallons of gas

[slicclex]

Yeah I tried replacing the fuel filter myself but didn't have a bigger bucket to hold the gas in so I just gave up. I think you'll find replacing the fuel injectors much easier than replacing the fuel filter. You might want them cleaned instead of replacing them, would help you save $$$ since Toyota injectors don't seem to fail.

[steve2006]

As this appears to be at a certain engine speed it could be the throttle potentiometer this is the black unit with a connector which fastens to the throttle body, if they get a dead spot on the track they get electrically noisy and may cause this fault.

If you have an old HiFi system the volume control ( the rotary type) would make the sound crackle when adjusted as it wears out or becomes contaminated with dust and this is in effect the same as a throttle pot.

[LexLuthor400]

Check all your vacuum lines. I had a jeep once that hesitated like that and I changed out alot like u did, only to find a leaky vacuum line. Problem solved, Hope that helps!

[92LS400...s/c?]

my check engine light came on and it said it had an egr malfunction so instead of replacing i deleted it since i am poor, the check engine light is now off; my vaccuum lines all seem to be in good condition and the car only hesitates when cold now. could it be the ports from the egr are so dirty on the intake that its still some how messing with the performance?

[jcrome04]

How much money did you spend "deleting" the EGR ??

[Lucky13]

Did you check the pump itself?

[92LS400...s/c?]

How much money did you spend "deleting" the EGR ??

like $15, I cut out some brackets for the EGR pipe and and the valve, than capped all the vacuum lines. I just copied the kit from lextreme; better than $100 for a piece of metal and bolts, and a lot better than $200 for a whole new valve. I noticed when I took the valve off there was a very large amount of "soot" I guess you'd say layering the intake manifold where it connects. I tried my best cleaning it but it was pretty tough and I didnt get it all off.

and when you say "did I check the pump itself" you mean the EGR valve? if so than yes I did; it was stuck closed...

So could it be that EGR build up getting lose and making something else mess up?

[Lucky13]

Well no you said you changed the fuel filter so I asked if you had checked out the pump itself.

[daffy]

I once had a similiar problem with my 1991 LS400 and finally found out the the distributor cap and rotors were at fault. When was the last time these were changed on your car? Daffy

[92LS400...s/c?]

Oh, well when I removed the fuel filter I would prime the pump to see if it was working and a nice flow of gas came out so it works fine.

As for the distributor cap and rotors, I think its been a while since they've been replaced; but, I might have replaced them when I changed the water pump witch was about 6 months ago now. I can't really remember I'll have to check on those.

[eatingupblacktop]

well i just changed the fuel filter and it fixed it quite a bit, it still has a slight hesitation but not half as bad as before, next im gonna try the injectors and see if that works.

you might want to try that too slicclex

Since you've seen improvement swapping the filter, it would seem fuel related. Injectors would be logical next step. I would also check the air supply. I know you cleaned the tb, but I would double check that there isn't a spot where either the throttle cable or butterfly are temporarily sticking.

[92LS400...s/c?]

well its almost a year later and my water pump went out again; so I replaced the spark plug wires and rotors and water pump again and what do you know the hesitation has gone away. the car runs smooth as ice again. I suspect the problem was the rotors, however on occasion at driving highway speed the check engine light comes on and says it's running lean...but it doesnt really seem to be. I wonder what that could be?