peterls

Only happened twice but I'd rather nip it in the bud:

1. I was going a little too fast, the light in distance turns red, and since it's a 1990 LS400 with not-my-favorite brakes, I put the shifter in neutral, to let it coast to a stop, with slight pressure on breaks. Within a few seconds, all lights are on on the dash my steering is stiff and I realize - the engine shut down! Never happened before, and never since. But I don't drive it that much, and not under those circumstances.

2. The next day was relatively hot, and a few times as I was decelerating to a stop, with my foot on the breaks, the engine hesitated as if it was going to stall. It did not, but it almost did. It typically wanted to stall when I was quickly braking to a stop sign or red light, from 40-50mph.

3. Since most of my driving is short distance, and weather is not hot ever around here, I think this has something to do with temperature as both of those times were longer rides and it was hot outside so car had enough time to get hot. (cooling system was normal)

Otherwise, the car drives like a charm. Perhaps the only other dislike would be that in the morning, it takes more than just a 1/4 turn of the engine to start it, but when the car is warmed up, it starts up like a motorbike - quick, easy and smooth, like "kh-wrooommm". I was thinking that maybe my ignition coils are getting old so they don't work as well when they are cold.

Based on search here, I am thinking perhaps that fuel pump resistor (although it should give me troubles when the engine needs more fuel, not less, right?) or fuel pump relay...

Any ideas?

EDIT: A few weeks ago I put in brand new EGR valve. About three months ago I replaced all spark plugs, wires, rotors, distributors, and even alternator, and thoroughly cleaned throttle body. About nine months ago I changed the PCV and the grommet that goes with it.

timmy0tool

iTrader: (7)

your idle control valve is probably dirty. clean it as well as your throttle body and intake tract since you're already in there. do not clean your AFM as they are prone to damage by cleaners out there!

i would do a tune up and replace the spark plugs, caps and rotors, if not already done recently. also consider that you may have failing capacitors in your ECU (common problem) as well.

Legender

Go with simple stuff first. Had a similar problem with a 95. Would die when coming to a stop off the highway. Cleaned the throttle body and put in new plugs. I think it was the throttle body that did it. Seemed it was starved for air due to the dirt when it tried to lower engine speed when warmed up. I'd look at that first.

Kram

check your egr system it does have a vacuum dash pot which alows the egr to open at high speed and if you put the car in neutal the only thing in commend is the speed sensor and vacuum which will allow the egr to open and the only thing that will close the egr is the dash pot which needs vacuum to close.just a guess but to test this all you need to do is block your egr vacuum and do the same thing that caused the first problem.If your check engine light comes on just remove your + battary cable for 30 seconds and you will reset the ecu.

LScowboyLS

the 95's actually had an ECU programming issue that could cause this - otherwise and for other years, it will normally be one of three things, dirty throttle body (especially 98 & up), dirty or failing Idle Control Valve (97 and earlier), or ECU capacitors (primarily 97 and earlier)

peterls

Is there a specific procedure how to clean the ICV (never took it off, so I don't know what I will find inside of it). Since I never touched the ICV, I imagine it is most likely that.

sha4000

iTrader: (1)

It's for a 90 but should be the same.

peterls

Thank you all for your suggestions. I am leaning towards trying to clean the ICV first, and will go from there. Since most of the rest of the engine was quite dirty, I would be surprised to find ICV clean...

BTW, it is a 1990, so those PDFs are right on the money Sha4000!

Kram, I am not familiar with vacuum dash pot - but would like to look at that too, so any pointers you have would be welcome.

peterls

OK, so I cleaned the IACV last night and repeated the exact same things to try to get it to stall, and it did not! Not even close - it just runs like a charm no matter what.
So I am 99% certain it was IACV. When I opened it, it was all covered with black soot and most importantly - the little plunger in the middle, or whatever it is called (valve?), was sticky and could barely move back and forth. I cleaned it all with my fav cleaner - B12 chemtool and some break cleaner in spray to help dry it - and the thing is moving smooth as silk. Some of the carbon was baked on, I had to scrape it off with my fingernails.

The only thing I did not like is that the smaller bearing (there are two of them there), is going bad. I can hear slight rattle and it does have slight bit of resistance when I turn it. I don't think it will fail right away, but I don't like that it is not as smooth as it should be, so at some point I am going in again and changing that one. I think someone (planet soarer?) has a write up which includes exact specs for the bearing.
Thank you guys for suggestions!
And, one more thing: IACV should really be on anyone's TO DO list as soon as you buy a used LS, because it is easy to do, and it affects the ride a lot.
OH, and I also noticed that idle was much more quiet and at lower RPMs from cold. Don't know if it is related or if it was just warmer outside, but usually I hated how high the RPMs were when I first start the car in the morning. I only tried it once, so I cannot wait until tomorrow morning to see how it starts, perhaps that was the only reason for too high RPMs while cold.