Bylan

Howdy all got a situation Id like some input on. I picked up a 1998 black/black nakamichi LS400 a month ago and did a lot of maintenance to it to make it a daily driver. The car has service records all the way up to October 2018 at Lexus of Westmont but needed a Timing Belt (15 years old) and water belt, as well as valve cover gaskets. I've largely finished up all those goodies, having done most of the same to my 1997 last summer. I also replaced the PCV valve, basically every vacuum hose, and deleted the Power steering idle up valve by installing a bolt in the pump and plugging the 2 vacuum lines on the intake manifold. When adding coolant and letting the car get up to temp, the idle began to slowly drop and stutter, getting progressively worse as the temperature needle rose to about mid way (where it sat before the t-belt/water pump replacement). No check engine lights, although CHECK VSC will display for a few seconds when I start the car after having the battery disconnected. I suspect this is just the vsc computer doing a test. The idle is steady at ~1000rpm when cold (I thought it should be a little higher but unsure) but as soon as the temp needle begins to rise, It gets rougher and It almost seems like a vacuum leak develops out of nowhere. When at operating temp, idling for ~10 minutes, the engine will nearly die if i don't give it throttle. I haven't let it run more to see if it will actually stall.

I have a few ideas of what the issue is. First off is just a vacuum leak, i haven't put all new hose clamps on everything yet as I just picked some up yesterday, but with how cracked some of the old hoses were, I cant imagine a loose hose is causing these issues. My next idea is the Idle air control valve, but with no check engine code I don't want to just throw money at it. I know a thorough throttle body cleaning would help too, and this being an old-man 2-owner car I'm sure it could use a good seafoaming, but the engine held a reasonable 600rpm idle before I wrenched on it. Another possibility is my TPS Connector, right on the throttle body where the throttle return spring is located, is cracked and broken into 5 piece. Not sure of where I can purchase a TPS connector, I guess Id have to solder splice the new connector in? Jiggling the TPS wires with engine running didn't seem to effect its condition. I have an obd2 reader and torque+ so I can view some diagnostic stuff. Id really appreciate the communities input on what I should look into, yall are always really helpful and I try to return the favor!

Fit1too

It is normal for the Check VSC message to come on once after the battery is disconnected. It goes away after a minute or so (the manual has info on that). I would check the throttle body and air passages and make sure they are clean, and it might help to fill the tank with quality premium fuel and take it out for a good run. Be easy on it for a while and then open it up a few times and see how it does. I have used Seafoam in the past to remove water from the tank. I have also used Red Line Fuel System Cleaner as well, but a tank of good fuel and an extended trip might do the trick.

bradland

Start with the easy stuff, throttle body cleaning and air mix path (see link), before throwing any money at it.

https://www.google.com/imgres?imgurl...&iact=c&ictx=1

Post a pic of the busted TPS connector, electrical connector housings are replaceable from a Lexus and/or Toyota dealer.

Losiracer2

I had a Check VSC code come up for the throttle body motor being bad, ended up cleaning it well and adding dielectric grease to the connector which took care of it and saved me from having to buy a throttle body assembly. I would check all connections first and clean all/lubricate all the terminals related to the VSC system with dielectric grease.

Bylan

I went through all the hose clamps and added a few gallons of fresh premium fuel, I have no idea what kind of gas was in it or how old it was. The idle still wanted to sit low when I initially warmed the car up but it began to step up in increments, like the car was relearning where to Idle at, and sits nicely at ~600rpm in drive now. I ordered a TPS connector off ebay, attached is a pic I am pretty certain it is what I need. I still plan to do an intake cleaning and maybe some injector cleaner through the fuel system, but the car seems solid and I'm beginning to daily it. Thanks for the tips guys!

YODAONE

If the wires are not damaged, and the contacts are intact, then all you need is the connector shell.

Do not hack up wires.

See:

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


If you are unsure how to do then ask Toyota or Lexus dealee.

Bylan

I will inspect the wires and contacts on the current connector very soon, as you're right about not wanting to mess with the tps wires. If they're undamaged, ill order a new shell, part # 90980-11150 if my research is now correct. For what its worth, I am experienced with soldering and I'd use proper shrink wrap, not the supplied garbage, and I appreciate your write up on installing new shells I hate dealing with those tiny pin inserts...

YODAONE

Verify connector shell.P.N.

It is stamped on the shell or ask dealer.

If the pigtail is a Sumitomo brand connector, then you may be able to remove contacts and use it....but highly recommend just buying from the dealer.
Few $.