AlaskanLS

Hello everyone! I recently cleaned IAC Valve on my 91 LS400. Now it idles rough. I used MAF cleaner to clean IAC valve. I didn't clean or touch MAF. I wonder what to do, should I buy another IAC valve or is it possible to fix the old one?

Spartan536

From what I have read the IACV should be cleaned with MAF cleaner so no harm there....

As for why it's running rough, did you check the bearings? As these cars keep getting older and the mileage higher the bearings have been known to go out, and I forget the specific type of bearings they are but I know you can order them online.

Here is an excellent resource, which I am sure you used since you used the correct cleaner according to this guide.

https://www.clublexus.com/forums/per...rol-valve.html

You might also want to take a look at this as well...

https://www.clublexus.com/forums/ls-...-macgyver.html

AlaskanLS

But it was running smooth before I cleaned the IACV. What bearing are you taking about, is it inside IACV?

Spartan536

According to some pages I have read there are 2 bearings inside the IACV that work with a magnet to open and close the valve, these have been known to fail over time and mileage.

Addendum: did you disconnect the battery before working on the IACV?

AlaskanLS

Cool, I will check them now and grease them if possible. Maybe MAF spray removed the grease from it.

AlaskanLS

You are the man, found the problem and fixed it, although it wasn't the bearing. When I dissembled the IACV to clean it inside out, I put it back togather with the tip all the way extended out. Actually the tip is screwed tight and if you twist it after dissembling it will come out. It has like screw mechanism, when you loosen it up it will extend and vice versa. It still idle a little bit rough but I think the computer will tune itself after driving it.

dicer

You don't tighten it in a certain position it has to be free to turn with the motor. And it has to be wide open when installing it.

AlaskanLS

Dang it now I have to open it again and leave some play in there?

AlaskanLS

Another problem emerged, the car is struggle to go fast and it feels like it's pulling a trailer. There is smoke coming out of the engine bay close to the exhaust pipe. I took it to a mechanic to check what is happen. Mechanic said the catalytic is clogged and told me stop driving the car until i replace the catalytic converter. But strangely there is no check engine light. What is the opionion of you guys? I parked the car for a mouth, before parking, it was running fine and now all the hell broke loose.

Spartan536

Have you considered a faulty ECU?

Question, did it smell like sulfur when running or a very strong gas smell at the exhaust?

AlaskanLS

It does smell like sulfur. I bought two catalytic converters both of them are universal from magnaflow. How many CATS does LS400 have? I am going to take it to welding shop tomorrow to replace cats.

Spartan536

That sulfur smell is the cat's getting red hot and breaking down due to a faulty ECU....

You might want to read up on this... it is an EXTREMELY common problem with LS400's especially the early to mid/late 1990's versions. Given you are driving a 1991 and I have a 1992 that had a similar problem to this, you might want to get your ECU rebuilt professionally.

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

Yamae and LSCowboy are the reigning authorities on the ECU issues, and LSCowboy rebuilds ECU's for a fee through his Facebook business page.

AlaskanLS

Damn it! I am confused now, What should I do replace the ECU and CATS or just the ECU?

AlaskanLS

Ordered an ECU also from eBay for 25 bucks. I believe it might be an ECU because my car kind started jerking when changing gear. It didn't do that before. And maybe the rough idle is partly caused by ECU too. But I think I should replace that CATS as well because it has 300 thousand miles on the clock and 91 LS400 has no sensor to tell you that CAT is up for replacement.

Spartan536

Problem with buying an ECU...

1. The "New" ECU you just ordered is likely still using the stock caps, they will likely be bad as well, this is a common problem with the capacitors being over 25 years old, you will need a rebuild to fix it.

2. That "new" ECU is not tied to your vehicle and will cause issues with your security system and will require reprogramming.

Just use the one in your car, get it sent out for professional overhaul by someone that knows what they are doing, and you get to disregard both 1 & 2.

I currently have my ECU out for the same exact issue you are having... not joking, this is why I have been commenting on your thread, I am dealing with it right now. My ECU is currently on it's way to LSCowboy for overhaul with brand new Nichicon, high ripple, low ESR caps. The cost for me was $248 which includes RETURN shipping, you must pay for outgoing.