91 Ls400 Will Not Idle

[Quack11]

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.

[Southern_NJ]

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.

Wow, sounds like you already went through a litany of steps to diagnose the problem. Sounds like a malfuntion on the fuel/air flow mix in regards to a sensor. I am not close to being a mechanic, but it sounds like something is trying to adjust itself to accomondate a problem.

Good luck and keep us posted. BTW, how difficult is it replace a fuel filter on a lexus? I know it is easy, once you locate it. I have a 2005 LS 430 and I want to change it. Do I just follow the line from the tank under the car? Does it just get clamped like a typical inline filter?

TTYS

GDF

[dcfish]

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.

Welcome to the club Check both coils and Plug wires for arching, They seem to cause problems that you describe. Or check this:

http://us.lexusownersclub.com/forums/index...ost&id=9897

[Quack11]

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.

[Quack11]

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.

[curiousB]

Well I'd look for some sort of air leak on the intake manifold if the ignition coils suggestion doesn't pan out. If you get out on highway with higher speed does it behave fairly well? Is this an idle speed issue or erratic engine all the time?

The IACV malfunction could explain erratic idle but the car should otherwise run ok at higher speeds.

You could also check fuel pressue with a guage to be sure its at proper PSI. Pump isn't only parts that effects fuel system pressure.

To save yourself a lot of time maybe you need a code reader to see what clues might be in the engine ECU error log.

[Quack11]

Well I'd look for some sort of air leak on the intake manifold if the ignition coils suggestion doesn't pan out. If you get out on highway with higher speed does it behave fairly well? Is this an idle speed issue or erratic engine all the time?

The IACV malfunction could explain erratic idle but the car should otherwise run ok at higher speeds.

You could also check fuel pressue with a guage to be sure its at proper PSI. Pump isn't only parts that effects fuel system pressure.

To save yourself a lot of time maybe you need a code reader to see what clues might be in the engine ECU error log.

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.

[oldskewel]

...

The IACV malfunction could explain erratic idle but the car should otherwise run ok at higher speeds.

...

Sounds to me like it is you idle air control valve (IACV). I have not had this go out on my Lexus, but have had very similar symptoms as you are describing on two different cars. Search around for instructions to remove and clean it. It may just have carbon build up, which you can remove with brake cleaner or similar solvent. Sometimes the cleaning does not hold and you'll need to buy a new part if the problem returns quickly. Good luck.

[VBdenny]

Although I have no exact way of knowing I do know that this is a very common occurance when the throttle plates get carboned up. I know there are instructions on how to clean this. I never had this happen on my Lexus but have had it happen on other cars. Clean the throttle body and see what shakes out.

[python]

2 causes of this condition...fuel or vacuum leak...no cel?a bad iac valve will cause sporatic idle, surging low then high,but i have yet to see cause a no idle situation

[Quack11]

2 causes of this condition...fuel or vacuum leak...no cel?a bad iac valve will cause sporatic idle, surging low then high,but i have yet to see cause a no idle situation

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.

[curiousB]

Good ending! Congrats.

[VBdenny]

Gotta love a happy ending. Nice repair job. Any chance you took pictures?

[Quack11]

Gotta love a happy ending. Nice repair job. Any chance you took pictures?

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.

[Quack11]

Forum, I got a MAF sensor and installed it on my car, check for codes and start it up. The car is back to normal and is driving just fine. Thanks for all the assistance and I am very excited to have it back on the road.

[Quack11]

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.

Forum, I got a MAF sensor and installed it on my car, check for codes and start it up. The car is back to normal and is driving just fine. Thanks for all the assistance and I am very excited to have it back on the road.

[glenmore]

Forum, I got a MAF sensor and installed it on my car, check for codes and start it up. The car is back to normal and is driving just fine. Thanks for all the assistance and I am very excited to have it back on the road.

New or used? How much was the part?

Thanks,

glenmore

[Quack11]

Forum, I got a MAF sensor and installed it on my car, check for codes and start it up. The car is back to normal and is driving just fine. Thanks for all the assistance and I am very excited to have it back on the road.

New or used? How much was the part?

Thanks,

glenmore

I got a used one, the MAF sensor and two hood struts cost me $14.00 (Yes, fourteen bucks comparing to the prices i've seen on the internet which exceeds $1,200.00) This seem to be a needed item in the LS400 community. I visited five junk yards, looked at over 13 cars and found it on the very last one I checked. The MAF sensor and the IACV was already removed from all the other LS400.

[python]

nice! glad u got this resolved