zeebaloo

Latest Update. I finally found some time to change the upstream o2 sensors. I went with the non generic type because they were in a cramped spot and I didnt want a dodgy wiring job to be hanging in that tight space. They each cost me $111 and I had previously bought some plastic ramps. It was quite a struggle to get the old ones off. On one, the connector was stuck and the second one was on so tight it took a very long wrench to finally twist off. And the result ... No luck, the problem still persists. The surgy idle and occasional sputtering - mostly when the car is warmed up. As before, sometimes for brief periods of about 20 minutes it runs perfectly, then goes to the kr@pper again. So to recap, changed the throttle body, cleaned the maf, changed the radiator (because I broke it :) while working on it), changed the pcv, changed the engine coolant temperature sensor and now changed the upstream and one of the downstream o2 sensors. I will continue to trouble-shoot. because I really enjoy driving that car when it runs well.

Thanks, I changed the gas several times and tried one of those fuel treatments to "clean out the injectors", it just cleaned out my 10 bucks. No updates yet, ran out of spare time these last few days, I will update when there is some news.

Here's an update. After putting the PCV valve back on and changing the ECT,I noticed a definite improvement. I disconnected the neg. terminal of the battery for half a day to clear all codes and memory (which I am assuming clears the computer memory). I drove the car on saturday night and it drove GREAT! like when I first got it, nothing went wrong. stopped, started, everything fine. I was convinced the problem was solved. Even the CEL was not coming on. But, the next day, after a short drive the problems came back again. Pause after initial acceleration and now some coughing noise like the TB door is opening and shutting rapidly, repeatedly. But ... the acceleration is sometimes very good and if I were to guess, now the TB doesn't go into limp mode. A smell of gas as if the car were running way too rich. I will continue to trouble-shoot this, but its quite strange that it worked so well for one night, then went back to the kr@pper. It makes me wonder whether the mechanic was right that I need a new computer.

Thanks Blake, Here's an update. After all the work so far, I am now only getting p0172's consistently, no more p0133s. i looked thru the trouble-shooting notes in one of the PDF, among other things they said to check the ECT (engine coolant temperature sensor). This was one thing I hadn't done yet, so I changed the ECT ($30) with one I got from pep boys. The old one fell apart in the socket so I had to change it. I don't know if it was broken before. Still getting the surgy idle, but I think the accel. has improved, I will have to test it over time. Took a look at the manual, it turns out you're right. The o2 sensor for bank 1 and 2 seem to be before the cabin, under the engine somewhere, the diagram in SF-86.pdf does not show much. So what in the world was I changing??? b1s2... doh! I must have got that impression from another tutorial on how to do it. So, I will test/change those. One other question, for a shot in the dark as someone recommended I changed the PCV valve. This turned out to be some trouble because what I wrote before. However, I am looking at the pcv and how it sits in the engine block, it is not fitting too tight, actually, I can twist it around and get it out quite easily. Is this supposed to be this way? I replaced the gromit and the valve and even the pipe. The gromit,seemed to go in about 98 percent of the way, couldnt get it to seal by itself, then I popped in the valve which sort of mushs in. Maybe I should have sealed in the gromit with some sealant before poping in the valve. What do you think? am I introducing a vacuum leak?

It was under the car, but the wire came up thru the bottom of the car into the cabin where there was a gromit and an electrical connection. Maybe it was one of the MILs that told me it was B1S1,but I can check the other too. Thanks Blake, I now have more to check out.

That's because it doesn't have one in a traditional sense. Look at the PDFs I posted; they are specific to the '99 LS. It shows that the ACIS VSV works with the intake air control valve to maintain the idle. Here's a real life shot of the acis vsv and vacuum tank (found it on CL): You mentioned wrestling with the carpet to change the O2 sensor, but the manual says that P0172 could be from Bank 1 or 2, Sensor 1 which are the sensors before the cats. Which O2 sensors have you changed so far? Thanks, Somehow I glossed over the PDFs. Was under the impression that PO172 was only for drivers side before the cat (B1S1). This is what I changed. That installation went smoothly. I had to pull up the carpet under the brake and gas pedals. I am getting a little intimidated to pull apart the intake to expose the Intake air control valve, but maybe I can change a part of the VSV ACIS circuit. They mention testing it with a Lexus hand held tester, do you recommend I buy one of these things? I only have an OBD2 reader. I have to say, I am starting to think I had multiple issues going on. The surging idle and the hesitation on accel. Maybe they are unrelated as sometimes I notice that idle is more steady, but I still get the hesitation problem, and now during the hesitation sometimes a misfire or two. Yes, I am still driving it to test it out and for short trips.

Yes, I saw the Intake air control valve, seems to be shaped like some figure 8's and inside the intake manifold,I don't believe this is the same. I tried the PCV valve($5.00) and a new gromit(around $6.00) and after a comedy of errors; the gromit fell into the hole, had to buy some needle-nose plyers($8.00) to fish it out, the pcv hose($16) snapped in half with the slightest movement, it does not seem to be the fix I was hoping for. The old valve did not look so bad but I changed it anyways. and the idle still surges. Also, I noticed a hose neck from the air resonator (that weird black rectangle of plastic attached to the air intake) must have snapped off at some point, I jb-welded some copper pipe to replace the neck and sealed around it. While getting the new valve, I spoke to the service guy at the stealership, he offered to check the car out for $220 and if they repair it, to put that towards the repair. His theories were unimpressive; new plugs, maybe a bad cylinder, but, the offer was still tempting.

Do you know the name of this sensor? I have similar issues on my 98. Thanks,

Still looking for that IACV :), in the meantime, I changed the O2 sensor using a generic bosch sensor, and for 10 great minutes it ran perfectly. Then of course, as this problem is intermittent, it started the hesitation again. After a few more minutes it got as bad as ever. So ... PCV is next, however, this part had to be ordered and should come in a few days. For those minutes, got no codes at all,then the P0172 came back again and some MIL indicators.

thanks, and thanks to blake, this is exactly the same as my engine. Haven't found iacv for a 98 on at least two parts sites. Today I blew about 50 bucks on some new 12k LB plastic ramps and pulled the 02 sensor, so I am already committed. It was surprisingly easy except for the part about wrestling with the carpet. I will pick up a new PCV when I get a new sensor, so we shall see.

...bump... So as it stands now, there is no good pointer to the location of the IACV for a 98 (I say 98) LS400. Until now, all pics have been from RX300 (Not to sound ungrateful for the attempted help), and I have since pulled the computer codes, I had already purchased pdf manual sets, so far they dont point me to said valve. I dont believe there are vacuum leaks, the mechanic would have probably found it. My thinking now is to proceed to replace 02 sensors. would like to hear from any LS owners with IACV exp.

The story continues ... I bought a scanner because the pep boys were never avail to pull the codes. 55 bucks, hopefully a good investment. The codes are; P0172 - Too rich bank 1 (something like that) P1780 - Park Neutral Position switch Malfunction P0133 - P0133 Lazy O2 Sensor Bank 1 Sensor 1 P0500 - which I believe is speed sensor. But, today when limping along, started to feel some transmission jerks. Not sure whether this is a symptom or cause.

Yep, this looks like an RX300. My LS400 TB assembly looks nothing like this.

Wow, thanks, but this is not my engine. It looks like an RX. I have only one TB and there is no IAC inside the barrel.

To further beat a dead horse, I bought a manual (a non-hyperlinked set of pdfs) for the ls400 (1998-2000) and did a search on "iac","isc", "idle air control" and "idle speed control", nothing turned up. Maybe it could be part of a graphic and not searchable, but it seems that it is just not mentioned. This is what led me before to believe that it may not have one. So if someone has a picture of this, it would really help. :)