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90 Ls400 Sputtering/rough Idle/no Power/ Misfire


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Hello I am a newb here but i have found many helpful tips off this website so i decided to join, but enough of that i Have a 90 ls400 with 178,000 miles on it the engine was taken out on flushed 6 months ago and i just changed the spark plugs(bosh fusion) the spark plug wires, rotors, and caps, air filter, fuel filter, and engine oil. Here are my problems I was almost on empty when i took off from a light and my car lost all power seemed almost like a fast idle i could barely get up the slope of the road. i looked under the hood when i got home and the engine was shaking and running really rough, i was able to determine that in was misfiring on the passenger side of the engine and i noticed that my passenger catylac converter was glowing from excess gas being poured into it so i replace all the spark plugs this fixed the glowing but nothing else. s0 I plugged my car into a computer and i got error codes for the mass airflow sensor and the intake temp(2 in 1 piece) so i went to the parts store where they said it would cost $1000 for a new sensor!! or $400 for a used!! so i went on ebay and bought one for $100 :D i replaced my old one with this one but i still have the same problem. i believe it could be my ignition coil because if i switch the ignition coils around the misfiring moves to the other side of the engine. the fuel pump is working fine and i cleared the cylinders of gas a few times by removing the efi fuse but so i was able to take the possibility of a fuel issue out of the equation. i ordered a new ignition coil so we shall see if this fixes it. also i had a quick r-12 to r-134a conversion done and now i have a high piched whine with rpms and my a/c get warm after a while of being on. and another thing i have a small leak by my catylac converter because i am missing a bolt is this a serious problem? should i fix it soon? now to my electrical problem after i plugged the computer in my tilt on my steering wheel no longer works.. i have yet to check my fues but i will post what the outcome to all of this mayhem is when i get it figured out but any help will be greatly appreciated..

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Your rough idle/no power sounds just like my '90 LS when the idle-air control (IAC) valve when out (after I washed the engine and didn't cover the IAC completely).

But of course there might be any number of reasons that might cause the same symptoms.

Good luck !

DT

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well i put in the new ignition coil and i still have the same problem just not as bad, but therewas a wierd metal rattling in which i never did find out where it was coming from, but do you think the random missing could be because i have a duralast ignition wireset and bosch spark plugs instead of the oem ignition wire set and denso plugs? because i read that people had problems with aftermarket ignition parts and problems with bosch

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Welcome, Seems like coils were your problem. Trying to fix electricals is risky...

well i put in the new ignition coil and i still have the same problem just not as bad, but therewas a wierd metal rattling in which i never did find out where it was coming from, but do you think the random missing could be because i have a duralast ignition wireset and bosch spark plugs instead of the oem ignition wire set and denso plugs? because i read that people had problems with aftermarket ignition parts and problems with bosch

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Your rough idle/no power sounds just like my '90 LS when the idle-air control (IAC) valve when out (after I washed the engine and didn't cover the IAC completely).

But of course there might be any number of reasons that might cause the same symptoms.

Good luck !

DT

where exactly is the iac? becasue i already replace the mass air flow meter becasue it went bad..

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It sounds like your belt may be off. you said that the engine was removed and flushed so the timing belt may be off. Go to Lexls.com and you can see pics of the timing marks. The Bosch parts may be the issue also. the IAC is under the Power steering pump and has two hoses connected to it one from the intake the other from the intake manifold.

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THE IAC IS NOT ON THE PS PUMP!!!!!! please do not post if u dont know what u r talking about....the IAC motor is located on the intake, also the chances of it being your timing belt is remote, one other thing, i recommend putting all OEM parts for the tune up, especially the wires, they come with all the plastic routing and mounting that runs in front of as well as the valve covers, u just lay them down and hook them up to the proper place on the caps, your distributor caps have numbers on them that corrispond to each cylinder,depending upon which head u have it on, some have circles on them and some dont

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the timing is not off also the engine had no problems after it wars flushed it ran perfect. the iac has not been touch and is working properly. My problems started occurring a few days after i changed my plugs, and when i went to check to se if i could figure out the problem i noticed one of the plug wires had a chunk melted off of it exposing the wire, so i replaced the wires with duralast wires and this made no difference in th performance it probably made it worse. :( so i hooked a computer to it and it told me there was a bad mass air flow meter and intake temp thing was bad so i replaced it and i replaced one of the ignition coils do to me being told it could be that but it made no difference. also the misfiring is random in random cylinders and its not a gas problem, because my catylac converters will glow from the non burnt gas dumping into them. and it does the same thing with the original plugs and the bosh platinum 2, and the bosh fusion iridium plugs i bought because i thought the platinum 2's had gone bad. i was told that high end cars like this are very picky with after market parts so i am under the impression that the duralast wire need to be replaced with oem. i replaced the after market caps and rotors with the original ones, but i already threw away the original wire set so its to late to salvage them but hopefully oem wires will fix the problem.

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u hooked a computer to it? the check engine light should have been on with a bad air meter problem......get all new parts from the dealer so u can rule that out as a possibility

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well the check engine light has not come on and now that i reset the computer in the car the mechanic has found no error codes, but he did recomend using oem ignition wires to see if thall fix the problem and he said if the wire melted it may have gorunded out? i dont know what this would do or how to fix it..

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well the check engine light has not come on and now that i reset the computer in the car the mechanic has found no error codes, but he did recomend using oem ignition wires to see if thall fix the problem and he said if the wire melted it may have gorunded out? i dont know what this would do or how to fix it..

I'm not sure I understand what's going on here. What's your mechanic's opinion as to the problem with your car? There are all kinds of test available to determine whether parts and systems are working or need replacing. What tests has he done? Has he told you to replace everything mentioned? If so, get your old parts back along with the money you've spent so far and get another mechanic. It sounds like he's guessing or taking you for a ride. A competent tech should have solved your problems by now. Do you know if your cel is working? Even though you've reset the computer, if the car is still running the same, you would have new codes generated if the computer is working properly. How has he determined that you should replace your ignition cables? Has he done continuity and resisitance checks? Get specific information anytime your paying a tech to service your car, and and be sure to keep the old parts. Also, imo, oem is the only way to go for just about everything Lexus.

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well the mechanic i only paid for the advise and the computer stuff(because i normally work on American cars and this electrical stuff gets tricky on these Japaneses cars..)i put all exsisting stock parts back on the car except the ignition wires,(because i threw out the old ones), spark plugs, and top ignition coil(because old one was cracked) and it still runs exactly the same rough idle and no power with random misfires. I am going to take the wires out and test the resistance so if anyone may know what it should be at that would be helpful. I went to lexus today and the mechanic said that it was most likely my wires because lexus' are very picky(he never saw my car because he charged a heavty fee to look at it lol)

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  • 7 months later...
  • 8 months later...
What ever came of this?? This is the exact problem I'm having... I wish people would post what solved their problems so that everyone can benefit... :chairshot:

I am having the same problems.. it would be good to know what caused this problem... missfiring and rough ilde. Was there a solution to this problem??

thanks

great advice here..

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I didn’t follow the original thread but it seems to me the problem needs to be diagnosed a bit further.

Is it A an idle problem or B rough running at all throttle positions?

If A then I’d look to:

  1. Dirty Throttle body, take apart and clean.
  2. Sticky or dirty IACV, take apart and clean, replace if necessary.
  3. Vacuum leak, fooling MAF sensor. Check for disconnected or broken hoses. Was manifold removed recently (to repair starter motor)? Not using a new gasket or improper reassembly can result in vacuum leaks.

If B then I’d look to:

  1. Plugged or partially plugged catalytic converter creating engine backpressure.
  2. Ignition problems. Lots of issues with wiring and coils arcing to chassis thereby causing cylinder misfiring and loss of power. Search forum on distributor issues, very common.
  3. MAF sensor bad or dirty. Unable to accurately read air flow, try cleaning but be careful, delicate device.
  4. Engine coolant sensor faulty, causing ECU to send improper fuel mix.
  5. Fuel pump or fuel regulator unable to deliver proper fuel pressure at all engine loads. Buy a Fuel pressure gauge and check fuel manifold pressure.
  6. Faulty injector(s) maybe a couple aren’t opening and closing properly.

I’m sure there are many more possible scenarios but these seem pretty common issues in this forum.

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hey curiousB...great post!!! As for me, i had asked the same question a few months ago because my 93 ls400 was doing the same thing. i replaced my drivers side coil and fixed the whole lack of power and rough ideling...also when i bought the car it was doing the same...rough ideling and wouldn't go over 15MPH...i adjusted the TPS and that was it... a slight turn of my TPS and drove the car home!!!I would check the other coil and adjust the TPS and see if that helps.

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  • 11 months later...
  • 1 year later...

Your rough idle/no power sounds just like my '90 LS when the idle-air control (IAC) valve when out (after I washed the engine and didn't cover the IAC completely).

But of course there might be any number of reasons that might cause the same symptoms.

Good luck !

DT

i washed my engine on my 1992 ls 400 and im getting a bad misfire , i get the car reved up to 400 rpm then let go the idle drops then i kept my foot on the pedal and my cat on the driver side started to glow red ,then i checked if my spark plugs went bad and alll of them have carbon build up there brand new plugs , i dont know what this could be from do i have a bad coil or bad iac?
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You "washed" your engine! What came over you? Why did it need washing?

So you now have water in all the engine covers over the plug wires,all over the distributors,all over the coils in fact everyting electrical.

If the cat is g;owing red you have unburnt gas going into it.

Start with drying out the engine, get some compressed air in there and try to remove as much water as possible, then get a hair dryer in there and continue drying with a little luck it may be enough to get the engine running correctly again.

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I took apart everything got the spark plugs dry , there was no water in the dis cap or roter thank god I went to the Ralph's used auto parts picked up 2 new coil packs and a iac valve going to install this today and hope she fires up and runs smooth I also picked up engine electrical cleaner from Lordco. Going to get going on this and hope it work s

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