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charlesranderson

Hot Speed Limit

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Hey gang,

I have a 91 LS400 with 139K. All maintenance has been done and has run very well. Replaced transmission fluid etc at 135k.

Was driving in rush hour traffic, stop and go for about 45 minutes yesterday going home by a different route than usual. At a break in the traffic, I tried to accelerate, but it did not immediately respond, then only went up to about 20 mph. I gave it more gas, but the engine did not rev higher and speed remained the same. I tried letting off the gas and then gradually pressing the pedal again, but same response and topped out about 20 mph. Engine temperature gauge showed normal. I stopped the car and there was some smoke, toward the rear of the engine compartment. On inspection, there is some leakage from the transmission pan evident, but the transmission fluid is not low and is not bad. Some power steering leakage also discovered.

After sitting off for two hours, symptoms were not evident last night nor again this morning. Really scratching my head on this. Will fix the transmission pan seal and the power steering leak, but am not thinking that was the problem with the speed, particularly when the engine would not rev higher with more gas. Could this be the throttle position sensor or mass air flow sensor or something else.

Any suggestions appreciated.

post-53431-1224351347_thumb.jpg

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Sounds like for some reason it went into "limp-home" mode

You say the symptoms have stopped?

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Hi: I tend to think that the Mass Air Flow Sensor went bad temporarily, like it was clogged with something and then it became free, or it is failing electronically. I would clean up the sensor in question, and if the problem returns I would have it checked the the Ohmemeter for the resistances. Had similar problems with two cars and it was the Mass A/F sensor. Check also the state of the air filter if it is very dirty from running on dusty roads that may be the problem. Fixing the leaks is a great thing, since it could kill your alternator being an early model. Check also your grounds in the engine make sure they are not corroded the same with the battery charge status and terminals. If the problem persists you might want to have the tranny sensors read, and while you at it take the valve body out and have it clean up by a pro, making sure also that your tranny filter and magnets are ultra clean.

CPR

Please post when issue is resolved with the cure/s. Thaks

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Sounds like for some reason it went into "limp-home" mode

You say the symptoms have stopped?

Symptoms have stopped today. Have it into my certified Lexus mechanic (JPImportz) to take a look. Would hate to be to far from home and get stuck. May know more Monday.

Thanks for the inquiry. Will keep posted on this.

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Hi: I tend to think that the Mass Air Flow Sensor went bad temporarily, like it was clogged with something and then it became free, or it is failing electronically. I would clean up the sensor in question, and if the problem returns I would have it checked the the Ohmemeter for the resistances. Had similar problems with two cars and it was the Mass A/F sensor. Check also the state of the air filter if it is very dirty from running on dusty roads that may be the problem. Fixing the leaks is a great thing, since it could kill your alternator being an early model. Check also your grounds in the engine make sure they are not corroded the same with the battery charge status and terminals. If the problem persists you might want to have the tranny sensors read, and while you at it take the valve body out and have it clean up by a pro, making sure also that your tranny filter and magnets are ultra clean.

CPR

Please post when issue is resolved with the cure/s. Thaks

Am having it looked at. Appreciate the ideas. I am fascinated by the Mass Air Flow sensor and will look more into that--a good cleaning would not hurt the sensor

Will post the solution. Probably Monday or Tuesday time frame. Thanks

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my car got the same symptom but only when i go over water. running in rain doesnt matter, but whenever i drive over a water pond at around 40mph, i could run only less than 20 mph. Hoewever, the car always comes back normal after 1-15 minutes of driving under 20mph. this has happened at least 4 times until now, and i dont have any clue.

it looks similar to your case,

mine is 1990 LS400 with 100k+ on it

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this has to be a fuel delivery,or an air flow problem..... if u had a bad sensor a check engine light would come on...keep us posted please

also,if it doesnt do it when the mechanic is looking at it he might not be able to find the problem

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Sure sounds like the ignition coils or their wiring.

Let us know the answer, pls.

Still running fine today. I could find nothing--certified lexus mechanic could find on error code 24, but that should not affect the speed limit. Power steering pump not leaking on alternator, but Rack and pinion is leaking--looks like that replacement happens tomorrow. Will keep all posted on symptoms and cause. Thanks

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Sure sounds like the ignition coils or their wiring.

Let us know the answer, pls.

Still running fine today. I could find nothing--certified lexus mechanic could find on error code 24, but that should not affect the speed limit. Power steering pump not leaking on alternator, but Rack and pinion is leaking--looks like that replacement happens tomorrow. Will keep all posted on symptoms and cause. Thanks

Been a couple of weeks now with no recurrence. Rack and Pinion replaced (power steering pump was saved!!) and new head gasket seals. A vacuum hose was disconnected and reconnected. Plus realignment and oil and filter change. All for the good, but it seems nothing would have directly caused the symptom. Fortunately, nothing now leaking or smoking under the hood. May have somehow related to overheating in the extensive stop and go driving.

I appreciate all of the ideas which were brought forth. May have to come back to the well on this problem again. Have heard that there are at least a few who have had similar symptoms.

Any thing new develops, I will post.

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