LS - 1st and 2nd Gen (1990-2000) Discussion topics related to the 1990 - 2000 Lexus LS400

Rough Idle After Water

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Old 09-10-17 | 01:41 AM
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Default Rough Idle After Water

Hey guys.

I degreased and hosed off my underbody near trans and engine to try to track the source of a leak and now it feels like my car is missing.
Idle seems ok in N and P but misses in D. While accelerating there is a clear miss. All plugs are new and firing. Im pretty sure this was caused by water as its too sudden an coincidental. Are there any sensors or connectors around the trans dipstick side that could cause this? Letting it dry tonight. Will spray some contact cleaner around tomorrow. Fingers crossed.

91 celsior

Last edited by Moarpower; 09-10-17 at 02:42 AM.
Old 09-10-17 | 03:07 AM
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Just remembered, While driving the catalytic converter light came on for a moment and then went out.
Old 09-10-17 | 09:18 AM
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maybe you got an oxygen sensor wet somehow?
Old 09-11-17 | 12:51 AM
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Likely that something got wet. The issue is still present after 2 days so I guess a sensor is damaged.

​​​​​​it is possible that this issue was present earlier as a slight knock ( or so I thought) while idling in drive . Now it is clearly running g rough and not firing on acceleration. It is idling fine in neutral.
Old 09-11-17 | 04:24 AM
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Hey guys. Tomorrow I'll get under the car and start checking sensors. Any in particular that will make the car feel like its missing ?

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Old 09-11-17 | 06:39 AM
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Originally Posted by Moarpower
Likely that something got wet. The issue is still present after 2 days so I guess a sensor is damaged.

​​​​​​it is possible that this issue was present earlier as a slight knock ( or so I thought) while idling in drive . Now it is clearly running g rough and not firing on acceleration. It is idling fine in neutral.
I'd check the cap and rotor by taking it apart and see if there is moisture in there(especially the one on your right hand side). If the cover wasn't tight you could have gotten some water in there.
Old 09-11-17 | 08:20 AM
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I've had this problem before after cleaning the motor of my mom's 95... check the spark plug holes for water. I found water had gotten in the tubes and puddled around the spark plug shorting them out and causing the rough idle. You'd think with the caps this would not happen but it did. Once I remove the water and cleaned them up using compressed air to blow out the water, they did fine.
Old 09-11-17 | 09:18 AM
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I would not assume something was permanently damaged by the water just because it's still bad a couple of days later. It might just need more time to fully dry out. Leaving it parked with the hood open, in the sun, will help.
Old 09-11-17 | 09:51 PM
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So I removed 3 leads and found some moisture on the coil plugs and the plug tubes. Let dry, the a little Co tact cleaner. Ran well for a few kms then started running g really rough and the cat warning light with Japanese writing came back. Maybe a sensor on the passenger side cat area was damaged?
Old 09-12-17 | 04:55 AM
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getting frustrated now. Got her up on the stands and will hook in tomorrow. Any advice is appreciated
Old 09-12-17 | 05:33 PM
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I second the cap and rotor housing getting moisture in there, but that should also cause rough idling in neutral as well. the USDM cars don't have that cat light so I am unfamiliar with what it means. is it for cat efficiency? overheat?
Old 09-12-17 | 05:55 PM
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Originally Posted by timmy0tool
I second the cap and rotor housing getting moisture in there, but that should also cause rough idling in neutral as well. the USDM cars don't have that cat light so I am unfamiliar with what it means. is it for cat efficiency? overheat?
Id say it is a heat light by the look of it. Hopped under this morning and checked to find a cat 02 sensor that was only finger tight and 2/3 of the way out. Id say this is the culprit. Disconnected and car ran the same. Reconnected and dc'd the other side and car ran worse.

Ill tighten it back up and pray but id say its damaged. May not be the issue but my guess is that it explains the light.
Old 09-12-17 | 08:50 PM
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Cleaned the right hand side (drivers side) 02 sensor and installed it again. Idle seems better by a big margin, however, on acceleration between idle and 800rpm, whilst in drivem there is still a very rough rev range.
Old 09-12-17 | 11:00 PM
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pulled off the rotor housings and there was no trace of moisture in either. It seems to take a few minutes of running to get really bad, feels like a restriction or like its not firing.

Seeing as the vehicle is a 90 model I will look into the price of new caps and o2 sensors regardless.

Could it also be a failing cat? Would that lead to similar symptoms? I do notice that the exhaust gets much hotter than it should and often creaks and crackles loudly for quite a while after shutting off the engine
Old 09-13-17 | 08:00 AM
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Noticed this wire below the rotor was exposed.


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