Someone mentioned about the trunk hinge, That is a new line of thought, why would you say that? I also am goinjg to try to clean the MAF sensor, and clean the throttle body, I got some Synthetic Fuel injector cleaner, and put that in. Talked to a mechanic friend, and he seems to think it might be the MAF sensor, possibly being dirty, as he has seen other makes of car, doing this surging, and they have cleaned the MAF sensor, and it worked.
He mentioned the "trunk hinge wiring" b/c that is known to cause all kinds of electrical problems with so many things in these cars. Idk if it would have anything to do with the surging though. Your MAF is actually an "AFM" and if you do clean it make sure you use the right stuff (search) and be very careful with it. You can do more damage then good. (personal experience )
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Thanks for all the replies, re my surging problem and the dash lights going on and off and then they totally go out, but will come back on overnight. Someone had mentioned about the trunk wiring harness. I have got to check this tommorrow. I was thinking the dash lights were wired with the ignition switch., as they come on when the car swtich is on. I am thinking now, may be in the timing,, previous owner had said he had put in new spark plugs, but I am now not too certain he had it timed. I will let others know, what I find out. Thanks to all that replied to this newbies questions. This is a great forum, I am very glad to be able to be a part of it.
The car runs runs smooth, when idling for the most part, until you accelerate, W Murphy
Again, please confirm that you checked that your air breather intake is not getting clogged by a sagging hood insulation as I mentioned earlier. I had exact same symptoms on my '93 $0 fix doubled the HP
Thanks for everyone's replies, I have changed the MAF from another Lexus I had that was running good, and it did not help it. I don't think it is the coil, as I had a friend, who had coil issues, and his just would quit when it got hot. Mine starts right up, and you can drive a few minutes, until you accelerate and then it starts the stalling, then surging, and I hve kept it from totally dying, by just letting off on the gas and easing back down slowly on it.Also something else I have noticed, is that my dash lights started going on and off, when this surging problem started, not sure if they have any connection to it, but they might stay on a few seconds when you first crank car, and then not sure if it connected to the surging issue, but seems to occur about the same time it starts, the dash lights go on and off and now are off
don't worry about the instrument cluster lights it just need to be replaced. my lights do the same thing on my car but no other other issues with it.
Do NOT try to clean the AFM!!!
Any oils/cleaners/etc that come in contact with that sensor will render it worthless!!!
It is possible to clean it but it's an all day affair which is NOT simple and CAN destroy the unit!
If your AFM module/sensor is bad the ECU will throw a Trouble/Diagnostic Code 31!
Put a piece of wire or paperclip into terminals TE1 and E1 (center and top left corner of the front-most 3x3 terminal section on my 94 but double-check inside your car's Diagnostic connector cap in the engine bay), then turn the key to on (without starting the car) and watch for flashes of the Check Engine and O/D Off lights...
Note that in some instances if your gauge cluster lighting is flaky the Check Engine Light and O/D Off light won't work properly so if your gauges aren't lit solid you might have to fix them first.
To read what the ECU is trying to tell you just count the Check Engine Light flashes which will be a somewhat fast number with a brief pause followed by a similar pace for the 2nd digit, followed by a slightly longer pause before flashing the next pair of digits if there are multiple codes, followed by a longer pause before it starts over and repeats all codes again.
If there are NO codes it will just rapid flash indicating an "all good" condition as far as the engine control unit ("computer") knows. Same with the O/D Off light reporting any electronics based transmission issues.
Note that some reported codes may or may not apply as the ecu stores codes until either the ECU gets reset or the battery is disconnected/dies. If any codes are found, reset the ECU (pull the EFI Fuse for a few minutes or disconnect the battery for a few minutes) and then drive the car until it acts up again and then put the diag jumper in and check for codes again.
I recently bought a 1993 Lexus LS400 and had the same problems with jerking and surging.It took 6 months to get the problems solved.But I finally got it straightened out.You have to get the TPS in just the exact position where there is no continuity showing on an Ohm meter.I am including some instructions from Google.Also,my fuel filter was changed out due to clogging,new tranny filter/screen,and new type 4 fluid.This helped a lot.But finje tuning and tweeking of the TPS should solve your problem.
6) Connect an ohmmeter to the IDL and E2 terminals of the TPS. Unless the throttle body is removed it's pretty much impossible to do this using the standard ohmmeter probes. There's just no room and plus you need to be able to rotate the TPS. It could probably be done using some very tiny clips.
7) Turn the TPS clockwise until resistance on the ohmmeter is gone and then tighten the two screws.
8) Now use your ohmmeter to check for continuity between terminals IDL and E2 with the 0.40mm thickness gauge still inserted between the throttle stop screw and lever. There should be continuity.
9) Now insert a 0.85mm thickness gauge between the throttle stop screw and lever. There should not be any continuity.
10) Replace the throttle body cover, plug the connector back into the TPS, and go for a test drive.
And now for the Lexls.com method...
My method relies on knowing the correct idle speed and doing a little trial and error. It may not be as elegant as the official method, but it does work.
When the TPS is turned as far clockwise as it will go the idle speed will be at its highest.
When the TPS is turned as far counter-clockwise as it will go the idle speed will be at its lowest.
Normal idle speed is 650 RPM, plus or minus 50 RPM.
So by turning the TPS clockwise, which puts more tension on the sensor, the idle speed is raised. It's the same as when you put your foot on the gas and the throttle opens, doing this puts tension on the TPS. Since the sensor doesn't rotate much you can tell that small movements yield big changes in the idle speed. The range between highest and lowest settings on my LS was about 600-1300 RPM. My first test drive the sensor was set too low and it caused very jumpy highway performance. I then adjusted it a little higher and it was much better. Basically I fine-tuned the TPS until my idle was about 650 RPM and it drove smooth, both on the highway and in the city. Since it only takes a few seconds and a screwdriver to adjust the TPS doing it this way is easier.
When I purchased my 1993 Lexus LS400 Feb. 27 2013,little did I know the trouble I was getting into.I should have checked the car a lot closer so I blame myself as much.The front seal,timing belt & water pump,throttle body,TPS,new IACV,ECU,rack & pinion,new OEM EGR crossover pipe,exhaust gaskets,valve cover gaskets,new plugs & plug wires,speedometer cluster repaired,front wheel alignment repaired or replaced just to get it to run right.This LS400 was losing 1 QT. of oil every 65 miles.So something had to be done very quickly.I turned to my friends and after 6 months,the car is finally running decent.No more leaks and 6 months of going through hell to get it right.
All this work and parts would've run at least $8,000 to $10,000 at the dealership.But my buddies and Ebay helped me keep the cost down to around $3,800.00.It sure helps to have good friends that are honest and dependable.I',m glad the car doesn't have traction control,that's a plus.And just 159K miles,way below average miles for this model year.I also purchased a good used factory Pioneer radio/CD player to put in it and a good used temperature control unit that's not blacked out.That's all that's left to install.I was very lucky to find a volume **** for the Pioneer on Ebay and very lucky to find all these parts at a fraction of the cost on the bay.I'm hoping I got my MPG back up to at least 24 to 25 on the highway.It does run a lot smoother after I very carefully set the throttle position sensor at just the right spot.It took me 6 months to get the car right.But it took a lot of patience.I'm just glad the nightmare is over and hope nothing else goes wrong.
Maybe he got lucky and a previous owner already had the ECM fixed. Doubtful though...
Once you get a properly working ECM and get the old age servicing done these cars are nice and comfortable and smooth and so much fun to drive.
Originally Posted by LScowboyLS
well don't freak out, because it is not an expensive problem, but you can count on more weird problems to start at any time, as you are due for the known LS400 issue of failing ECU capacitors
I purchased a 1993 Lexus LS400 in March. I don't think I have driven that car a straight week since I purchased it. When I bought the car, it needed the instrument cluster fixed as there was no backlight and the gauges for the speedometer and fuel did not work. There was some jerking when I test drove it, but didn't think it would be too costly to fix because I wasn't in the "know" on the costly repairs for the Lexus LS400. Since then, I have had the transmission overhauled, the TPS replaced, a rebuilt ECU installed. After having my car at the mechanic shop for 2 months to install the ECU, it still would not crank. The mechanic explained the car was not getting any spark, but that it was getting fuel. He stated he thinks the problem lies somewhere between the crank position sensor and the ECU. The mechanic did not have time to put into repairing my vehicle after having it for two months, so I had it towed home where it is now. I remebered the mechanic informing me that he kept having to charge the battery when he did take time to troubleshoot the vehicle. So I purchased a new battery and installed it. The car cranked!!!! but it was short-lived because I drove it about 3 miles from my home about to get on the interstate when it started jerking and skipping and slowing down. I prayed all the way to the next exit. I noticed the jerking stopped as I eased off the gas pedal to slow down getting off the exit. So I drove it to the nearest auto parts store to purchase a battery harness to keep the battery in place. I came back out of the auto parts store and the ignition would turn but would not crank. I have an Excalibur Anti-theft system on the car (there when I purchased it) and thought the alarm had jumped to carjacking mode or something. I tried to troubleshoot the codes for the alarm using the alarm user manual for 3 days, still no crank. I disconnected the battery and waited a while and reconnected it, still no crank. At this time, the car would not make the "whirling" sound when you try to crank it. It just clicks. I tried searching my problems on your forum but there are so many things to check when you're having these type of problems. Based on what I've read, it could be fuel pressure, alternator, spark plugs and wires, trunk hinge, fuel pump, Mass Airflow Sensor. Do you really have to go through the process of elimination to pinpoint what need to be fixed?? Can anyone give me a good solid lead on what to check based on the symptoms? I am so, so glad that this forum exist! Thanks, guys!