Hello everyone, i am new to this forum, so far i like this place. lots of good information on here. Well, I am having a problem with my car that i am sure someone on here will know what's going on with it. I am going to describe this the best i can.. Ok First off, the car is a 1993 Ls400 with 113,000 miles. The problem i am having is that when the car is driving and it gets to around 40 to 50 mph or lil higher, or the rpms are at almost 2000 rpm or a little over and under, the car will start bucking severely. if i step on the gas it will stop for a second only to return. i have been driving the car with overdrive off and its not as bad because the rpm's stay at a higher Rev. I can also tell that when idling in park or drive the car is shaking and seems to be stumbling. I just replaced wires and spark plug's and air filter and cleaned maf with maf cleaner, and almost forgot, also replaced throttle position sensor.. The car also has lack of power at low end until the revs go up over 4,000 then the car will pull good. Also seems exhaust has a weird smell to it.. now here is the real weird thing. When i unplug the maf and drive like that, the car runs and drives like new!!?? So i thought it was the maf. i have tried 4 diff mafs and its the same thing! when the maf is plugged in, car runs like garbage, unplugged, runs great. no mechanic can fig this out. ran code check, no codes in computer.. The mechanic said when the maf is unplugged computer goes in default mode and there could be a sensor bad, but what sensor could it be?? there are no codes in the computer! Anyways, sorry for the long post, i hope someone can help me, i haven't had the car long and i love the Ls400! i just want her to run right.. thanks very much in advance to anyone that can help me fix my Ls400!!



Ricky..

 

I just checked the fuel pump, it is making weird sounds and its pulling nearly 23 volts. is it the pump or the pump ecu? can someone plz tell me where the fuel pump ecu is ? Thanks in advance..

 

Could be a multitude of issues, any error codes?

Tune-up, plugged injector/s, O2 sensors, other sensors, ignition wire, cap, rotor, coil, fuel pump relay, clogged up air filter or fuel filter...

Rather than attempt to do a step by step fix is take the car in and plug it in to get a list of error codes it may be throwing out.

 

Bought a new fuel pump. still didnt fix problem.. Does this sound like a Ecu problem to you guys?

 

I damaged my original maf (karmann Vortex meter) while cleaning & had many of the symptoms you describe.

They did not go away until I found a replacement. Did you clean all 4 mafs?

 

I only cleaned the original one.

 

I just found the problem, i am getting no ohm reading at all with the sub oxygen sensor. the one with the connector thats under the passenger floor board. here is the weird thing. even if i unplug the connector i do not get a check engine light!?!?!? The check engine bulb is good. do you all think this means my ecu is busted? thanks please let me know asap so i can find a ecu if need be. Oh and i am going to get aftermarket oxygen sensors, would u all recomend bosh or denso? thnks very much!

 

The O2 sensors past the cats are there only to keep tabs on the cats.

I'm thinking throttle position sensor or crank/cam sensor issues.

Also, do this:

Find the gray DIAGNOSIS connector on the engine or the driver's footwell, and with the key on but engine off, use a paper clip or a small piece of thin-gauge wire to jumper-wire terminals TE1 and E1 and that should give you the DTCs.

 

Hello, thanks for the reply. I tried that a couple days ago. no codes were set. I changed the Tps a couple days ago, didnt help a thing i have also put new cam position sensors on and crank sensor. I have spent nearly 1,500$ on this car in the last month or so. i bought it with this problem because the guy that sold it to me told me it was prolly just the maf, i think now maybe it was a mistake. but i thought it was a good deal, a one owner 93 ls400 with 112,000 miles. So is was your saying when i unplug the o2 sensors after the converters there is suppose to be no check engine light correct? also, there is no ohm readings on that sensor. thanks for your help, i am so upset with all this, i appreciate any help i can get. i may just have to break down and take it to the stealer or get rid of the car, i really dont want to do that, i can tell its a very high quality piece of machinery, i have owned quite a few cars and the Ls seems higher quality than even all the mercedes benz models i have owned.

Thanks again...

 

Just go to the dealer and get a diag. With all the money you're spending and hoping to find the problem, just nip it in the bud so you can get this issue solved. This is a great car and it's a treat and blessing to own. I'm sure you'll find the problem and be a happily ever after lexus owner!

 

Yea, i just am worried about spending more money at the dealer because i took it to a shop close by that works on mercedes and lexus, and they hooked it up to a diag machine and it showed nothing the guy said, maybe lexus will have a diff machine they can hook it to or something. One thing i just dont understand is that when i unplug the maf sensor all these problems go away, its so weird..

 

have you been using a new maf or junkyard?

 

Hey, I went and bought a refurb one. Before that, tried 3 from the junk yard. Hey i notice you are from louisville, I am In Etown. You know where that is?

 

Good morning,

Kind of sounds like a fuel/air or ignition problem to me. Attached are a MAF and ignition problem section from my 1997 manual. Probably a little different than your year, but take a read and maybe you will get some ideas.

Also, when you replaced your plug wires, did you use OEM or an aftermarket brand of wires? On another board recently, I read of an owner that used aftermarket wires and they caused all kinds of problems until he replaced them finally with OEM.

With respect to how it runs when unpluging your MAF: When you do this, the computer no longer knows how much air is flowing into the engine. Because of this, it doesn't know how much fuel to inject in order to maintain the correct air/fuel ratio. So it reverts to a safe mode by injecting more fuel than actually needed (you would rather run with too much fuel [rich] than too little fuel [lean]). Perhaps when you get in this mode, by unplugging your MAF, the extra fuel being dumped into the motor is really just hiding your other problem and your MAF isn't malfunctioning at all.

Good luck!

 

Here is the ignition attachment...