Purevenom1

Hello. This is my first post on this forum and hoping I can get a resolution to my problem that I am having. I am from NC just outside of Raleigh.

Got a 93 LS400 that has a problem that I can not figure out. Have searched for the solution through several websites and search engines. Also have looked through the repair manual several times.

When you are sitting in the car with it running and you floor the gas it cuts out and only goes above 2K rpms. It also does it when you are driving down the road and you floor it to get up to speed or to pass. Have checked everything that everyone else is saying was there fix and still no luck.

Pulled the codes on it last night and it comes back w/ Code 41 for the TPS sensor. And all of the ones I have looked at for similiar issues never respond back to update the threads so it is a never ending cycle. Any info would be appreciated.

bagyo

i've got the same annoying problem with my 92 LS. Here's a very recent thread yet again with another LS with same problem. 1993 Lexus Ls400 Surging and losing power WMurphy covered a lot of bases already and still no luck! Take a look at it, maybe it might shed some light on the on the surging.

Purevenom1

Yea I have seen that already. Thanks. I have already did the plug wires since it was due for some. That didnt change anything. Checked the coils and several other sensorsand they all checked to be good. Replaced the coolant sensors since I saw where that was the cause on one of them and its still doing the same thing. Going to put on a new TPS and check the fuel pump later on. Just didnt know if there was anything definite since they are so many related issues.

zukikat

Did you test the TPS, which I believe should be listed in the service manual as to how to test it and what resistances should be found between which terminals, not to mention properly adjusting it as you'll notice that the holes for the 2 screws that hold it on are both slotted so that it can be adjusted?
I'm making assumptions about that as I've only owned my 94LS400 for a week but at first glance it appears to be pretty much the same as teh TPS on my 1992 Turbo Supra and the Supra's factory service manual explains full testing and "calibration" (adjustment) procedures in full details...
If you decide to replace yours you will need to know that procedure anyway as it's NOT just a unplug and unscrew the old one and reverse those two steps to install the new one, the new one will have to be adjusted. It's not hard with a set of "feeler gauges" and a basic volt/ohm/multi-meter.
Years ago a Toyota dealer broke the retainer clip off my Supra's TPS connector and it fell off when I hit a big bump on the freeway and it would randomly switch between not wanting to run below 2k rpm's and driving fine back and forth at random as I limped it home but it was throwing a TPS code and I saw the connector dangling when I opened the hood so I plugged it back in and the problem disappeared.


My LS400 that I bought a week ago with 185k miles on it (according to the gauge cluster's built-in digital odometer which may or may not be original to this car) will go from cruising fine to acting like I'm rapidly switching the key on/off/on/off/on and if I take my foot off the gas pedal at decent speeds it usually settles down but not always and if I'm at really low speeds and turn the steering wheel it WILL stall almost every time.
It also lights the check engine light when it's stumbling and the light goes back out when it jumps back to normal life and it fires right back up if it stalls and I bump it to neutral and hit the key. So far I haven't been able to put the diag jumper in to check for problems while it's acting bad but I've checked it less than a minute after it settled down (by the time I could pull over and get stopped) and there are no trouble codes reported at all which makes it very difficult to troubleshoot and no fun to drive. If it were my car's TPS I'm confident that it would throw a TPS trouble code so in my case I really don't believe that's my car's problem but it's possible that it might be yours.

Note that I've made two 2.5 hour interstate trips in this car and it ran normal all the way there and acted up once as I hit an exit for a food stop but yesterday after I replaced a faulty Air Flow Meter sensor module to correct a Code 31 and thought was the culpret and was test driving the car the Code 31 problem seems to be solved but the stumble/stall issue still flared up 3 times in maybe 20 miles of mixed interstate and city driving so the bad AFM sensor wasn't what's causing the stalling problem with my LS.

It just got new timing belt, water pump, pulleys, front seals, distributor caps/rotors, Iridium spark plugs, valve cover gaskets, valve clearances inspected, thermostat, full transmission fluid/screen servicing, all new Toyota/Lexus fluids, power steering leaks all fixed, gauge cluster lighting and gas gauge flakiness fixed by me, new hood shocks, and a few other maintenance things, and I thought I was down to just seat belts that won't retract and really bad brakes (horribly warped rotors) but apparently I now have to chase down an intermittent stumble/stalling problem that isn't throwing any codes, damit.

Purevenom1

Yes I have checked the TPS the other night and it is reading w/in range. also tried another just to make sure. I have cleared the codes several times and the same one keeps popping back up. Code 41. There is not check engine light on or it doesnt come on when the issue arises. Just when I check the codes it is there. When I clear them and recheck there is not any.

When I jumped the wires on the port under the dash that is what I get. There are also 2more to jump to do a drive test on and the same thing happens. I ruled out the tps so then I went to the ECM and test the TPs circuits there according to the manual. On one side of it I am getting the correct volts and such. On the other side I am not.

SO I am almost but not certain that it is the ECM but will find out if I can get to the local junk yard and pull one for 35 bucks and try that. If that is not it I will just take it back and get a refund.

If the key is on the start position and I do a full throttle push the code comes back whether the car is running or not. It also seems to be running real rich when I do it while its running since it smokes up the garage when teh smell of burnt fuel . I will post back when I can figure anything esle out. Thanks for the inputs so far as I know this issue is lingering around for a lot of LS400 owners.

zukikat

It doesn't suprise me that it's complaining about a full-throttle start attempt as it's expecting to see the IDL (idle) position at the TPS and I'm guesing that your pressing of the pedal (moving of the TPS off the IDL position) has it wondering why it's seeing someting other than IDL.

I don't have a TPS code and the AFM code I was getting seems to have been resolved after I replaced the AFM sensor module but I've decided today that my ECU is faulty and probably causing at least one of my random drivability problems, if not both.

Yesterday I experienced an issue my mechanic buddy who did my timing belt/water pump, etc described to me today and it basically rendered the car undrivable and unsafe as it wouldn't accelerate to save its' life (a bicycle is faster when my LS is in that state, I"m not kidding) and the ECU wouldn't even go into diagnostic mode to display any trouble codes when the diagnostic jumper was inserted, and wouldn't reset, and after sitting for about 10 minutes it would finally begin responding to the insertion of the diagnostic jumper but it would "stumble" the flashes while flashing the "all good" status about once every 10-30 seconds at random (both the CEL and the O/D Off light would "stumble") which leads me to believe that my car's ECU (ECM) is in the process of failing.

If I leave the car sitting for a while it fires up normal and runs/drives normal with no CEL and no codes and then all of a sudden it either starts acting like I'm rapidly turning the key on/off/on/off/on/off/on while I'm driving and then jumps back to running totally normal with no lights or it just flat out stalls with no warning and lets me restart and goes back to driving normal for moments or minutes at a time and then does it again whenever the mood strikes it and it lights the CEL as the tach falls to zero then the CEL goes right back out and the tach jumps back up, or the other problem is it suddenly stumbles and lights the CEL then starts idling either really high or low and running unbelievably rich and seems to just totally stop managing the ECT portion of the transmission at all, and I can walk faster than the car will accelerate in Drive, although while it's in that state the car will fling gravel and accelerate like crazy in Reverse which to me indicates that the tranny is running entirely off the hydraulics and the ECM has yanked the timing back rediculously and set the fuel to "pig rich" to prevent potential engine damage and has gone into "Limp It Home" mode for whatever reason.
But the fact that while the ECM is in that state it won't acknowledge the insertion of the diag jumper and the fact that it reports "all good" when it finally does "see" that the diagnostic jumper is actually inserted, and that the CEL misses/stumbles while trying to flash the "all good" status totally points to either a major wiring harness problem or more likely the ECU in the process of failing...

I kept wondering why the lady got rid of this car because although it needed a timing belt and water pump and brakes and had power steering leaks and the flaky dash illumination and would throw an AFM code on decel once it warmed up, every time I test drove it with both city and 90mph interstate cruising it seemed to be fine and it looks great on the outside and really good on the inside and everything INCLUDING THE A/C still WORKS!

Plus it went 2.5 hours to the mechanic's place at slightly over posted speeds on the interstate and made it back like everything was fine so I was really baffled why she got rid of it.

Now I know...

But it's not catastrophic, it just sucks.

The problem with a junkyard ECU is that it could very well have the same problem or be in an even worse state of failure which could potentially have caused an LS400 to be wrecked or if it's not wrecked it probably went to the scrap yard because it wasn't running right or at all...

I went to my local Pull-A-Part about 60 miles away today after my LS decided to become undrivable and they had FIVE 1993's and TWO 1991's and a 1991 and someone took all but 3 of the ECU's and out of those three, one was from the 1990 and sitting in the back seat already, one of the 1993's it was still mounted and plugged in but some dumb-*** took the lid off and let it get rained on (I'm NOT kidding!), and I found another 1993 ECM sitting in the TRUNK of the 1990 with junkyard yellow marker pen writing on it like it's already been returned, yay... I bought it anyway for $25 with 30 day refund/exchange insurance but my hopes aren't high that it'll be any better than mine and I'm not even sure if it's the right one for my base-model LS (No Trac or VSC in mjy car) because I have no idea which of the 93's in the yard it came out of.

Oh and ALL of the gauge clusters were gone, ALL of the AFM sensor modules were missing from the AFM housings, and the one 91 and one 93 that still had climate panels in them needed new lcd display screens, damit...

But at least I got a new pair of perfect fog lights for like $10 for the pair, YAY!

Tomorrow I'm going to try the ECM I bought and see if the car will run on it or not, then if it will I'm going to just drive until the car gets stupid again and then immediately try that other ECU and see what happens because I already know my ECU won't reset or respond to the diag jumper right away, so if an ECU swap while the car is pissed makes the car run again then it's probably NOT a harness problem, just a dying ECU.
At least that's the line of thought at the moment anyway, assuming the junkyard ECU is even working at all...

I hope that helps you at least a little?

deanshark

Purevenom1; Check your ECU ports again, it's always good to check it twice, ya never know. It's nice to have the manual, isn't it? If you can get an ECU for $35 it might have it's own problems. But if your J/Y lets you return it, might as well try it. Hopefully the problem isn't in the harness b/c that would be pretty hard, and time consuming, to find. Gl

zukikat; I hate to say this but try shortening your posts and get to the point. People tend to skip such long posts, especially when 3/4 of the post has nothing to do with the question asked.

Purevenom1

@Deanshark
It sure does make it alot easier when you have the manual. Found it on ebay for $10 free shipping. Has everything in it and is on CD.

Yes I have checked them a few times with the volt meter on different settings to makes sure that I didnt miss anything or screw anything up. I have a buddy coming over this w/e and going to get him to do the same just to verify what I have done. Its always good to have a second set of eyes looking at it in case I missed something. Yea the j/y has a 30 day return. It is one of the pick and pull yourself. Just hope they have one out there if not looks like I am looking on car-parts.com for one or Advance for a new one.

I dont think its the wiring harness since that is the only thing showing up like that. All of the connections are tight and secured.

Dtwillis5

I'm in the same boat with y'all my car starts up and when I give it gas it cut off if I ease on the gas it go to 1700 rpms and cut off.

deanshark

I thought you had the full size 2 volume service manual. But hey, if the CD works for ya that's good for $10. I paid almost $200 for the books but I can have them out with me on my car. lol
I see you're from NC, which J/Y do you use? I had, and am having, problems with Standridge trying to get cash back for something they didn't ship. What a hassle. Even though everything else on the harness looks good you could have one wire that's not. Don't rule it out untill you know for sure.

Purevenom1

Yea I love the CD. Got a laptop in the garage and I can bounce back and forth throughout it instead of having 2 or 3 books to hunt though. Both have their pros and cons thou.

Yea I am still looking to narrow it down and get a fresh set of eyes on it. If it is still the case then we are going out there to see what they have. It was running fine and then all of a sudden it started doing this. My aunt owned the car before and she was very to the point on the service on it since her son works at the car lot. Only other issue is the gauge cluster but that may get fixed sometime down the road ssince it doesnt interfer w/ driveability.

I am always looking at LKQ since they are right down the road from me. Last time I was out there they had 3 or 4 LS400. A few were in worst shape than some but hey I got a fairly good starter from one as a back up to rebuild cause the one on mine was completely shot to the point of not rebuilding. Got that for 25 bucks and it looks like its been on for 3 or 4 yrs from Toyota/Lexus.

Purevenom1

OK say I was bored while ago and went and pulled the ECM out just to kill the curiousity. Pulled the covers off and this is what I found. Think this could rule out the TPS since the readings I am getting are whacked out. Not sure if this controls part of it or not but it can't be good.

twofanman

Looks like you may have found the problem. I hope so anyway. So what's the plan? Are you going to send the board in for repair or try to replace the caps yourself?

tomtheslac

Watching this closely...

Purevenom1

I am looking into getting the capacitors shortly but just have to make sure I get the correct ones. Anyone know which ones will and will not work.

100UF10V 105 degree C H9235 C105
10UF50V 105 degree C H9235 C103

Havent looked at RadioShack yet but I doubt they have them. But hopefully they will.