I have the dreaded 40mph hesitation problem with my 1993 LS400 120k miles. After doing a thread search on this issue, there was no clear fix for the problem (lots of questions but no solutions).

I've replaced the timing belt, water pump, plugs, wires, TPS, cleaned the MAF, changed the transmission fluid, etc. and still have the problem.

The problem seems to be worst when:
1) The tranmission is in OD and the torque converter locks up - slight hesitation up to heavy "bucking" is felt when trying to slightly accelerate.
2) The transmission is in D with the overdrive disabled - surging is felt when the throttle position stays constant or slightly accelerating.

Stand still part and full acceleration is fine.

Thanks,
Steve

 

i feel like i have the same symptom as you, i have a 92 LS 400 with 185k on it, and when i step on the gas pedal to accelerate, my rpm goes up to about 5k and it just stalls, i have a feeling it my transmission but im not 100% sure...

 

Sorry to bump such an old thread, but I'm having the same issue with my 93 LS with 190k on the clock.

The problem seems to have gotten more pronounced after I changed my plugs, wires, ECT, and cleaned my TB. I've also performed several transmission drain and fills with Toyota Type-IV. For the last drain and fill I changed the filter and cleaned the pan/magnets, but the problem still persists.

I intend to replace the caps and rotors when I do a timing belt change in the next few weeks and I'll probably replace the TPS while I'm at it as well. I'm hoping that this will cure the issue, but from the OPs experience in changing these parts, I'm worried that it might not fix my issue.

Is there anything else to look at after the caps/rotors and TPS are replaced besides the O2 sensors, ECU and MAF? Faulty Coil, crank angle sensor, cam angle sensors? I'm just not sure since I am not getting a CEL, and usually when these type of sensors go bad a CEL is tripped and the car will run like complete crap.

I wonder if there is a problem with my EGR system that is causing this hesitation...?

I do have a TRAC light on caused by what I think may be a bad wheel speed sensor (Code 43)... Could that cause a hesitation issue? I wouldn't think so, but I've seen and heard of crazier things than that.

Thanks in advance for any advice!

 

cation,

Hopefully, this will correct your issue also...

I bypassed the EGR system. I simply unplugged the EGR valve (large electrical connector on the round device on the right side of the upper intake manafold). There were no codes set by the computer and it now doesn't surge or hesitate on throttle tip-in.

It has been running this way for over a year without problems. I plugged it back in lately just to see what would happen and the hesitation immediately returned.

-Steve

 

I've been wondering about the EGR system! Thanks for the advice viper.boy!


Update:
Just tried this, and it seemed to improve things vastly... I'm still getting a little bit of a hesitation under certain conditions so I think I'll test the TPS and replace it as necessary. A full EGR system delete is in my near future.

 

interesting, thanks for the info!

 

I just did this and it solved the symptoms that viperboy had described...also, I noticed my gas mileage went up again! Anyone have similar effect? I had thought the EGR system would improve mileage, not ruin it...

 

http://www.lexls.com/tutorials/emission/egrfilter.html perhaps?

 

Nope, nope. Did that and the car still ran with the hesitation problem. Unplugged the EGR sensor and the difference is night and day.

BTW PD, did you ever figure out what was causing your poor mileage problem? I would try unplugging yours and seeing if it improves. My guess is that if the EGR sensor is bad, it will send a bad signal to your comp and the car's A/F runs differently, because I definitely notice a MPG improvement.

 

what poor mileage problem

 

https://www.clublexus.com/forums/ls4...-tooo-low.html

Ha, it was on a really old thread (my mistake). I was just wondering if you ever solved why it was so low.

 

car was totalled before i got to it.

 

Hmmm, anyone else tried this lately? my 92 does this when the overdrive is off. Haven't looked at it but is there just a wire harness to disable it or does it involve disconnecting hoses?