gmacrae

I got sick of my 95 LS400 stalling when pulling up after a long highway cruise. I had cleaned the throttle body, cleaned the IAC valve, replaced air filter etc etc, and the problem persisted. It definitely seems like the ecu closes the IAC valve when cruising at highway speed, but forgets to open it back up when you pull up to stop. I refused to just get into the habit of turning the a/c on when pulling up. I dont like my chances of finding a replacement ecu here that actually sorts the problem.

My fix required about 30cm/12" of vacuum hose (2-3mm i/d), and a single T piece (4mm i/d).

The aim was to feed the engine a small amount of extra (AFM metered) air, so that when the IAC stays shut, the engine is still able to feed itself enough to keep idling.

First, cut the vac hose that runs down from the intake to the power steering, insert the T piece inline, then run the vacuum hose from the T to the little unused nipple on the intake toyota conveniently left for us.

This basically increases the engine base idle roughly 300rpm thanks to the perfect size of the unused nipple. The ECU just adjusts the IAC to keep the idle speed where it should be normally.

This also stops the 'jerk' when stepping off and back on the gas when cruising around 80km/h.

Hopefully that does the trick for the rest of you. Questions/comments welcome.

*** UPDATE - this fix is still working perfect roughly 6 months later ***

Gene

DA51

I was wondering if this tiny bit of air has made a difference?
On the SC page a Toyota Mechanic said that the ISC Valve should removed and cleaned as preventive maintenance.
Viewing the tiny vacuum that you attached compared to the vacuum attached to the ISC, would not the engine need more air at idle?

gmacrae

Yea, i've been running it like this for months now, going great.

I tried cleaning out the ISC valve, it made no difference, it was already pretty clean.

I dont get your last point? You realise the car still has the stock ISC valve setup right? It just has the vacuum line i installed as well to allow a small amount of air into the engine with the ISC closed.

j three

I thought there was a service campaign that Lexus put out for the early ucf 20's that altered something in the computer to fix this. If you are not the original owner you should check out the service records to see if this has been done.

McSwine

I wonder if this would work for a 2000 LS?

PureDrifter

iTrader: (10)

no, it wont.

besides, this problem never appeared on the post '98 VVTi engine'd cars.

McSwine

Thanks for your answer, but I can tell you with 100% certainty that this exact problem occurs on my 2000. Like the other dude stated, I have to turn on my a/c after a long freeway run or the car will stall (most of the time; seems to do worse in hot weather).

PureDrifter

iTrader: (10)

this symptoms may be the same but the actual CAUSE may be very different. the 95-97 had an ECU recall/TSB for this exact problem.

gmacrae

I wondered if lexus did a recall... I might give the dealership a call to see what they say

gmacrae

Just an update, still going perfect, no stalling problems since i did this.

Och

iTrader: (3)

Interestingly enough, on UFC10 that nipple is used - it pulls air through the fuel pressure regulator when VSV is open.

Mega

Thanks for this writeup. Doing mine today before a 50 mile drive on the highway.

Mega

Completed this this afternoon, still have the 50mph shudder, and still have the stall after a long highway drive.

Maybe this mod, and a combination of cleaning the throttle body, and cleaning the iacv help?

SRV1

iTrader: (2)

Two things to check are the throttle position sensor and the dashpot.

James

gmacrae

Yea if you haven't cleaned the IAC and throttle body you should, adding that little hose only allows a tiny amount of extra air into the engine, might not be enough to make a difference if both are still clogged with crap