Ok, this seems to be a major problem that I have not seen anyone solve yet. I have a 90 ls400. The engine starts up beautifully. Idles great around 1000 or so. Runs perfect when In open loop “cold engine” but once it reaches operating temp the idle drops to around 200rpm. Only when in gear. If it’s in park it bumps back up to around 500-600. Even at this low idle it has magnificent throttle response. Easily passes the wide open throttle test. Drives, and shifts seamlessly. But when coming to a stop the idle drops so low it’s wanting to cut out. If the engine cools below operational temp the idle raises back up to normal.

replaced the power steering pump and the silly air valve that goes with it.
tps sensor
ect sensor
distributor rotors, spark plugs, spark wires. Distributor caps.
iac valve motor
timing is set perfect

i can adjust the throttle cable to give a little more gas and that helps a little. I can adjust the tps and that helps a little. If I adjust them to where the car should sit at warm idle then it shifts hard. So I’m assuming I need to leave those at stock and not adjust. I can’t imagine I should be tuning the throttle and having to also adjust the transmission line just to keep good idle?

where and what is causing the idle to drop at operational temperate. I would be happy as can be if I could just keep the engine in open loop. I don’t mind wasting gas money. And the engine has so much power in open loop. I only use this car for racing all these little rice burners on the road anyway.

does anyone have any thoughts on what is causing the idle to drop, and or, how to get this car stuck in open loop?

MAF is reading that it is good.

 

Is RPM reading from instrument cluster tachometer or diagnostic tool reading?

 

Is RPM reading from instrument cluster tachometer or diagnostic tool?

It sounds like the former....

 

I use the tack on the cluster to judge. I was suspicious the tack was off so took it to a shop and paid them to run their own so I could see if mine was correct and it’s accurate. I could only pay them for 30 mins to use their tool as they wanted 400$+ just to inspect the engine and troubleshoot the problem.

 

All of this text and no mention of vacuum??

 

Yes all this text an no mention of vacuum. There are no vacuum leaks. Your title says Lexus champion haha that’s a joke

 

you could have mentioned that in your post. Anyway good luck finding the cause and please keep us posted on the root cause if it’s discovered. Cheers

 

The capacitors in your ECU are in good condition?
P.S. I just noticed I was annointed a Lexus Champion...and that's no joke.

 

the titles follow post count. They are set by the administrator

 

Ecu looks to be in immaculate condition

 

Just checked 02 sensors and they are good as well. I just read maybe I should of changed the ignition coils when I did all the sparks plugs, wires, distributors etc.

im still not convinced tho. I would understand if they get hot they might start to short but this is not the problem I have. The engine runs great. Even at the 2-300 rpm. She’s firing on all cylinders. And when the engine temp “radiator temp” cools below half “running temp” the problem disappears. The coils would still remain hot even if the coolant cooled down for a few minutes. As stated there is no vacuum leaks. When she’s on cold start I can cover half the MAF with little to no problems. Once it gets hot tho it seems to NOT want to suck in air. If I put 1 finger in front of the MAF she dies instantly.

 

The resistance in the MAF is reading the correct range. I am hesitant to change this as its expensive and I’m already 1200$ into this. No doubt the engine runs better than ever before but still has had no effect on the low idle once warm.

hell how hard would it be to just plug the fuel injectors and throw a carburetor on top with a Custome housing? My 78 Chevy “327” is sitting in my driveway laughing at me over how hard this tuning issue has become. Anyone here ever tried to just switch to a carburetor. I see they use them when breaking in these motors after a Custome rebuild.

 

Wow, that's not a good way to get an answer to your problem when he's just trying to help you. The "Lexus Champion" title goes by how many posts we've made. I wouldn't consider myself to be a champion but I do know most stuff about the LS400. So being up there to be "champion" I'm sure we've made plenty of posts and pointed out enough stuff to help out other members......nice members.

At this point it looks like you should have paid the $400 (probably less) to have the shop diagnose it for you instead of throwing parts at it and hoping for the best.

 

No that guy could of phrased his question in not an *** hole manner. Could of asked of simply asked if were any vaccum leaks. Not insult me and say I typed so much without mention of a vacuum. That’s why it’s a thread cause the thread will go on. Don’t need to put my life’s story in one post. I now see everyone in here is retarted. I’ll leave this site bye!

 

Think he was being humorous. (to other members) You being new here you wouldn't realize that. Ya gotta get used to the people and how they phrase or ask a question. I highly doubt he was insulting you, like you just did to every single person on this site.
Hope ya get it fixed and sorry to see ya go. Well...