Quack11

I'd do a search of this forum on wiring of distributor cap. I don't recall if it is the high voltage wires arcing to the engine block or the primary wires on the coil (shorting to frame due to pinched wire) but I have read a few posts about this. Those would be other things to check in addition to the cap as you noted. Thanks "CuriousB", i'll be doing a full inspection of the distributor and CPS as soon as I get back on that coast. I've bought an OBD I&II code reader to further assist with any codes that may not have been displayed and I hope to find and fix this problem. Will post the findings when complete.

I agree. IACV has no influence at higher throttle positions. I think you need to find out why the car doesn't ride well at higher speeds. If you still have an idle problem once that is resolved maybe more work with the IACV is advised. Until then I'd chase the big issue first. These cars are famous for issues with one bank of distributors going intermittent. That is an output device but it is not detected by the ECU so if it fails they'd be no code in the ECU error log. Are you sure there are no codes in the ECU giving further clues? As SRK points to input device there is a good chance that would throw a code. There are no codes in the error log, I will be scanning the ECU for errors again this weekend with an OBD I scanner to see if something was over looked. Which bank normally have problems and what are the trouble signs displayed? My guess is that there will be cracks, chafing or broken connection in these close tolerance areas. Thanks for your help.

I will take a look at that circuit and sensor to see if there are any problems I can identify. There is another post regarding this same issue and the poster said his fuel relay gets very hot. I've noticed the same with mine but I am not sure if this ties into the problem. Thanks for the input and hope this will soon be a happy ending.

The car will run fine upon initial start up at both high and low speed but starts to act up once it is warm, normally idle fine for the first 10-11 minutes. IACV check good when B1, B2, S1 - S4 was grounded, the audible click on shut down is also present. When the terminals were grounded the "open/close" travel was very limited so I took the valve apart. It was corroded from the electrical grease used during assembly, the grease was broken down and became hardened to the shaft which in turn restrict its full travel. Upon re-installation the can ran great for 20 miles and idle for 43 minutes without any problem. At high speed the car will starts to jerk/hesitate but it will continue until lower speed is reached or a complete stop. Putting it in N and staying on the gas pedal does not prevent it from cutting off but it will start back up on the very first turn of the key. I'll be installing the new/used IACV this weekend so if there is any other checks anyone can think of, please let me know. This is a 91 LS400 with 134K, it is well maintained, no maintenance was done to it prior to this happening, the ECU did not have any stored codes and the engine still sound like new. Thanks CuriousB for the assistance, let me know what else I can try over the course of this coming weekend.

This seem to be an issue with many LS400 and there are plenty different guidance and trouble shooting steps to solve it, I'm having the same problem with mine and still no resolution. Some of the steps i've done includes; removing the fuel pump and checking the output pressure, changing the fuel and air filter, checking the wire harness in the trunk for chafing, cleaning the MAF sensor, cleaning the throttle body/ butterfly, checking all air hoses for leak and cracks, removed and cleaned the IACV, reset the ECU (Clear the memory) check the TPS for proper operation, check the distributor, cap, wires, plugs, etc for serviceability, check fuel pressure regulator, EGR valve and all other sensor and part I came in contact with. After cleaning the IACV the car ran fine for 20 miles and the the ghost re-appeared. It's been parked since July 7th and have not moved an inch mostly because I am not home to continue further trouble shooting. My son starts it daily and he said it will idle great from a cold start for 10-11 minutes and the it shuts off. It will restart fine and will idle for anywhere between 30 seconds and 5 minutes and then shuts down. The car will start up on the very first crank but will not stay idle for long. If he tries to drive it, it will run fine and then the erratic idle starts. The only thing I did not check is the exhaust system so that will be one of the items to check. Most thread points to the IACV which cost over $1100.00 at most places, a fix I think is too expensive for the year vehicle. I got a used one today from the junk yard, will clean and install it when I get back to the East coast and let the forum know if it fix the problem. Good luck and keep us posted.

This seem to be a very common problem with the LS400 and i'm experiencing the same. I've done everything this site has recommended and the car have not moved an inch in the last two weeks. It will start at the first turn of the key and run for a few minutes before the erratic idle problem. If anyone has other ideas or solution, please post to the site.

Sorry forum but I am back. After a solid 24 miles of flawless engine ops, the same problem is back but not as frequent as before. Unfortunately I am heading to the West coast in a few hours and will not be able to troubleshoot this problem for maybe the next month or so, hopefully when I return it will have already fix itself. I will check the site to see what other recommendations the Guru will have for me. It is a myth buster but I will one day find the culprit.

This request is a bit old but here you go. starter.pdf

I've got the 91 LS400 and the amp is located in the trunk. Facing the trunk, it is directly behind the left aft passenger seat back and behind the carpeting. Make sure your other speakers work fine, check the balance, FWD, AFT, left and right operation. If all your speakers work the you will want to focus on the amp but make sure it is getting power and the harness from the amp to the radio is intact. I have the Panasonic system so I am not sure if the setup is the same. Good luck and keep the forum posted.

Get under your car and check the wire harness from your xmsn (transmission) for frayed, chafed or anything that may interrupt the flow of current. The speed sensor should be the only component that is responsible for this issue if all other inspections are GTG. Let us know the outcome.

To everyone, thanks for your assistance with this problem. I removed the IACV and did a few check/test provided by "DCFISH", the findings were very interesting and can be used later on if this issue is brought to the forum again. I check the resistance of the IACV and it was bad, I did the "open & close" check and it was also bad. I called the local auto parts store and was quoted a price of $1,121.79 cents (yes I am for real) I went back and dissambled the valve to check the internal condition and found out that it was corroded from the electrical lubricant used during assembly of the part. After years of wear and tear and heat subjection, the lubricant had become hard and formed an additional layer on the IACV shaft itself. This corrosion has caused the part to failed the resistance and operational check and also to move freely as it should. I cleaned it up to like new condition, re-assembly and re-installed the part. I am very excited to say that the car is now running like a champ again. I am up to 14 miles of test drive, abrupt start and stop, extended reversing, high and low speed and it feels like a new ride again. I hope this will be the last of this issue and again I appreciate the guidance from everyone to this resolution. If I can be of assistance to the forum it would be my pleasure.

Today I went back and start the car, it fired right up as usual and I drove it for 11 miles, the first 3 miles were flawless and then the ghost re-appear. At high speed there are no issues, it is mostly happening now at very low speed and complete stop. Today it did not stall but idle very low as before. It is an idle issue and not an engine problem. I will check the fuel pressure and I am also trying to get a code reader for the OBD-I system but I am not having any luck. I am in the process of buying one that reads both I and II system. Thanks for the help and please keep your suggestions coming.

Thanks for the welcome and info. I went out and recheck most of what was done and what you passed onto me, everything seem to be intact. I started the car and it ran fine for 27 minutes without any problem. I went to back it out the garage and all hell broke loose again as soon as I put it in "R" the idle issue start. I got it out and it did the same when in "D". I drove it for about a 1/4 mile and the car is not very responsive to the accelerator, it basically adjust speed on its own, all I do is steer and brake. Got back in the garage and it sat there and idle erratically forever without shutting off. Any other suggestion you or any other forum Guru may have? Thanks.

Looks pretty darn good, you must be proud of the new look. Are those seat covers and if so where did you get them and at what cost? I've seen plenty site offereing after market covers but never knew the final product would have such a professional finish.

The fuel filter is located forward of the left rear tire, it is covered by shield. The system is the hard line setup and you will experience fuel spill/ leakage during the process. Raise the car and have a container ready to catch the spill. I tie a rag to my forearm to prevent the fuel from draining past my wrist. Good luck and let me know if you have any other questions. I've owned my car for many years and only take it to the shop for wheel alignment, i've done all the maintenance on it myself, to include the timong belt.

Hi everyone, I am new to this forum and need your expertise opinion. I've owned my 91 LS400 for years and it is always properly maintained with 138k. About three weeks ago the car died at an intersection, after immediate re-start it started to idle very rough, RPM would go from 300 to 2000 constantly and then engine shuts down. I managed to get it home and the problem mysteriously went away for the next week. A week later it started to do the same thing, except this time as soon as I put it in drive it would hesitate then died. I have no problem restarting the engine but it will not idle for more than 30 seconds. I changed the fuel filter and engine started up fine and ran like an olympic sprinter for a whole 13 miles and then quit. As of this posting I 've been unable to move this car an inch, she still starts up on the first turn of the key but it will not idle past 30 seconds and it also idles very erratic during this time. Here is what i've done so far; changed the fuel filter, reset the ECU, removed and re-installed the same fuel pump, disconnect the fuel supply line going to the engine and check for constant fuel flow, cleaned MAF and TPS, cleaned intake chamber, verified the wire harness in the trunk in not chafed or broken, check all fuses, check for stored ECU codes, checked for leaking/broken pnuematic lines, sensor connectors and just about everything I can think of. I've owned this car for years but can't recall hearing the fuel pump running when the key is in the ACC position (it does not now, only when the starter is actually engaged). During the 30 seconds of idle i've disconnected the MAF/P, TPS and the difference can be heard so i've ruled out a bad sensor. The "check engine' light in NOT on and no maintenance was done to her prior to this problem, the tank was filled a few days prior and i've since drained and refill with enough to continue troubleshooting. This seem to be a problem with these cars but I think i've done everything out there to get her on the road again. Can anyone assist me further with identifying and correcting this malfunction. I am very familiar with cars and can find my way around them easily. Thanks and it will be a pleasure to assist anyone who may need it.