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91 LS sputtering issue

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Old 07-04-18, 09:37 AM
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AZBuman
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Default 91 LS sputtering issue

hey everyone got an issue if you guys can help. My 91 LS was sputtering while in drive and stopped at a stop light. When I drive it drives fine. Accelerates fine. When I stop at a stop light and put it in neutral it idles fine, no sputtering. Only while idling in gear does she sputter.
from searching Iím finding it could be o2 sensors causing the car to throw to much fuel while in gear. Does this sound right? Any other suggestions? Thanks and happy 4th.
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Old 07-05-18, 09:51 AM
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What is sputtering ? Running jerky? Missing? Popping noise?
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Old 07-07-18, 09:04 AM
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Sorry for the late reply. Up in the mountains with no service.
When I came to a stoplight the car would feel like it was about to die when it was in drive. But when I shifted to neutral it idled fine. It would go down the road fine, only while stopped at stop lights while in drive.
it would just run really bad and feel like it was about to die. I guess maybe sputtering was a bad word.
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Old 07-09-18, 04:18 PM
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Rough? Like 400 rpms? 600? Have you disconnected anything and not reset the computer by disconnecting the battery? Is the throttle cable loose or stretching over years? When was the last tune up with plugs and wires? Air filter clean? Is the MAF sensor dirty/ unplugged? If you do any of these reset the computer. Vaccum lines disconnected even a small one or leaking? Last oil change? Worn out oil will set off knock sensors. Last transmission fluid drain and fill? Broken key or casing?

Last edited by Michael88; 07-09-18 at 04:19 PM. Reason: addition
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Old 07-10-18, 12:47 PM
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Don't try to clean the air flow sensor that ruins them on that year car. Strange idle problems very likely idle air control motor. Also strange operating conditions can be the famous ecu cap problems.
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Old 07-10-18, 02:32 PM
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Nothing wrong with spraying a MAF with MAF sensor cleaner ... if you use any other chemicals you will ruin it.
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Old 07-10-18, 03:16 PM
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As dicer mentions about the IACV and ECU.

ECU thread here:
https://www.clublexus.com/forums/ls-...capacitor.html

A past discussion on the Karmen Vortex MAF :
Full thread:
https://www.clublexus.com/forums/per...o-clean-3.html
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Old 07-11-18, 02:33 PM
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Originally Posted by Michael88 View Post
Nothing wrong with spraying a MAF with MAF sensor cleaner ... if you use any other chemicals you will ruin it.
Again it is important that you don't spray cleaner of any sort into the Karman vortex air meter used on the gen 1 LS400's.
If you spray a fluid into it the mirror gets crap on it (a film from the cleaner) and then you pay $700 for a new one if you can find it. Your cleaner will work fine on a hot wire type sensor found in the newer LS400 models.
Please search out what others have said about spraying cleaner into Gen 1 air flow meters, it is a huge no no.

Last edited by dicer; 07-11-18 at 02:47 PM.
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Old 07-11-18, 11:11 PM
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when my 91 was at normal temps with low fuel (less than half a tank), it would cause to stutter and have no power. I changed out the fuel pump and fuel filter and it worked out.
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Old 07-11-18, 11:50 PM
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Good God do not clean the afm. Not on the ucf10 or 11. I had a similar issue an it was a bad afm. Could also be fuel pump or iacv
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Old 07-12-18, 01:07 AM
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Default Idle air control valve is gonna be the problem

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Old 07-12-18, 07:14 AM
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I have a 1990 Lexus LS400 recently had the same issue, I had the ECU tested replaced the Mass Airflow sensor, also replaced the fuel pump. My car ran fine while driving but stop and go traffic or sitting on the highway was the worse. Replace, **ENGINE COOLANT TEMPERATURE SENSOR** Autozone $30.00 took me 15 mins to replace I used a 20mm deep socket. I replaced that car idles great runs stronger no rough missing, also I feel the power as I come off a light.
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Old 07-12-18, 02:19 PM
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Holy crap, I didn't get notices that i had so many replies. Sorry I didn't get back sooner.

Michael88 - yes when I am stopped at a stoplight/sign the rpm's go from 1k down to like 4-600 and back again. Feels like it is going to stall. According to the sticker on the windshield the oil was replaced about 1k miles ago. The previous owner did it every 3k miles but took it to a jiffy lube/chain store. I will be doing that myself with full synthetic. Not sure of a tune up or wires but that was on my todo list with the vehicle. I'll be checking the MAF sensor, I do have some cleaner for that. Don't know about any of the other services either but the key is in good shape. It runs fine going down the road and idles fine while in neutral or park just not in drive.

Reading the comments I think I'll stay away from spraying the MAF sensor. One thing I also noticed was after the car was pretty well warmed up, the rough idle wasn't nearly as bad. At some short stop lights it wouldn't even idle rough. When it is cold it is real bad. There is a slight hesitation when I first take off too, but once it gets past the first gear, I am assuming, it takes off like a rocket. Kills my wife's sequoia, she hated that.
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Old 07-13-18, 10:05 AM
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Ok so the CEL came on and it took me some time to figure out how to check it. Finally got the codes pulled they are as follows:

41 - Throttle Position Sensor signal
71 - EGR system malfunction

Anyone have any ideas where to start with these. From the little research I 've done they don't seem to be huge issues. Now on to diagnose why the airbag light came on.
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Old 07-13-18, 04:56 PM
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See if you can clean the egr. Then chech connection on tps. Remove it if you need to. They are tricky to get back on
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