Engine Surges Then Dies. I Have Searched, But Have Not Found A Solutio

[fly_S2K]

Hello all,

Well it's happened to me, the dreaded surging idle and stalling engine that often occurs with our early gen Ls400's. I have searched but nothing's actually pointed me in the right direction with my problem.

Here are the symptoms. My 1990 LS400 drops to very low RPMs after a few minutes of driving. It will sometimes drop low then surge up to about 2000rpm or flat out stalls.

However, this does NOT occur after a long drive or anything, it will happen after 2 mins of driving. Even when I am driving around 40MPH, the car will slow down then start surging or stalls. No matter how much throttle I add, the car will drop RPM's (200-300RPM) then surge upwards or just flat out stalls. It will not allow me to drive.

I have spent 2 days searching on this common problem without results, as everyone else's seem a bit different. Such as the 94-95 with the ECM problem or 1st gen's like emyself doing a TB cleaning and MAF cleaning which solves the problem.

I've taken a look at my MAF and it looks clean. I'm not sure what to clean on the TB but I do not think that is the problem. I do not think it is the idle control valve because my problem will occur even when im on the freeway doing 60.

I want to say it is a bad MAF, but I don't want to go out and buy one without a second opinion. Could someone point me in the right direction? Any input would be greatly appreciated!

Thank you.

[akewlguy]

<------------ That way ---------------->

[93ls400walt]

Surging, per the factory chart is #1 SWITCH CONDITION SIGNAL CIRCUIT which includes the park/neutral position switch. The Air cond switch signal. And the Throttle position sensor. The second area to look at is the fuel pump control circuit.

These are listed as the #1 area for a prob. with surging, poor accel., Incorrect first idle, rough idle, idle hunting, high idle, stall after pedle depressed.

[RFeldes]

Check all your vacumn hoses since it is happening constantly.

[fly_S2K]

Thank you for the suggestions, I will check out those things.

[Alexi]

Keep us updated bro and good luck.....

Al.