UTGS400

For anyone having the low idle problem, I am trying to find out what mods you have done. After the dealership replaced all the parts in my car that could contribute to a low idle, they came back and told me that it is probably a defect with my PI TC (2800 stall speed). I don't think that is true.

The head tech told me that it might be the TC not closing properly. He also stated that he believes that after market intakes will also cause problems with the idle because the computer gets a false air temp. reading caused by the steel intake heating up.

I personally have come to the conclusion that the problem is related to a computer programming issue.


BTW, according to multiple Lexus Master Mechanics, our cars should idle at around 700-800 RPM with the A/C off, and around 900-1000 with the A/C on. As of right now, my idle is between 450-550 with the A/C off and around 650-750 with the A/C on.

Edit: Please post your mods that might effect the idle (if any) and tell me what your GS idles at both with and without the AC on. Thanks

JacobT

Chad,

I got the same answer from Lexus master tech. He thought the metal pipe of SRT intake caused the higher intake air temp. I should put back the stock intake to see it it would fix the low idle problem. My car currently idles at 625 rpm with AC off.

I think it's the Lexus ECU programming problem but I really do not think Lexus will fix it.

BananaGS

ha ha, welcome to the club, I don't have TC, just intake wECU, I made a bypass plug, it will bypass the ECU after my last finals and post some more result soon

Anh

jmecbr900

I have them both the TC and the intake/ecu combo, but I had low idle problems BEFORE I installed everything when the car was bone stock. What's the excuse then?

By process of elimination, we can rule out gas being the problem since people from all over the country have problems. We can rule out climate (humidity, temp, pressure) since again we have problems from all over the country not just one part. We can rule out the MAF since a few of you had it replaced as the "cause" of the problem and it didn't fix it. It would also be way too much co-incidence that all of us have a bad plug or need TB cleanings. As a matter of fact, I believe it was BananaGS that had most of his TB/intake replaced at the dealer as again the "cause" of the problem and it didn't work either. IMO the only common denominator is the years 98-00 and model GS400.

I'm with a couple of you; I think it's the ecu programming that's fried. Is there an aftermarket ecu available for our cars? or maybe just a simple swap from a newer model that doesn't have the problems? I'm not sure if it's possible. Maybe our local Master techs on the board can find out if the swap is possible w/o causing the car to catch on fire or something. Maybe then a few of us can try it to see if the ecu has anything to do with it.

Mr Johnson

I don't fall into the predefined categories but I would vote for some combination of ECU programming and "issues" with the TB/MAF.

If I leave my AC on (say auto mode) I will never have a problem with low idle and my car will idle at ~750-800 RPM. If I turn off the AC while sitting at a stop (car warmed up) idle will drop to 250-350 RPM and the car will either die or else the ECU "learns" something and idle comes up to ~500 RPM. After that first "learn" my car will then always idle at ~500 RPM with no further problems. This only happens once the car is warmed up and in closed-loop mode. While "cold" no problems with idle at all.

I've been eyeing a TEC3 unit given all the great buzz around it, maybe I'll take the plunge and see if I can program it to control our cars in a "stock" manner (time is my only enemy).

GSquicksilver

I have had an engine decarb (which i believe is fuel injection cleaning), new spark plugs, reset my ecu multiple times. All of that only made my rough idle "temporarily" go away. My car would idle at around 400rpm but would not be rough for a brief period after i tried the engine decarb with an ecu reset. But the problem came back, which i find odd that it normally occurs on HOT days. So last weekend i decided to pop my MAF sensor out and spray a few sprays of brake cleaner on it, and boy were the filaments shiny afterwards! So i put it back in and have been driving the car a few times already this week. I do notice that my car does idle smooth now, but there are a "few" instances where i would feel some roughness like if i came to an abupt stop. But most times now, my car is idling pretty smooth. RPM is still at 400 though which i find kinda odd. So i doubt it's the low RPM that is making the car rough since now my car is smoother even with 400 rpm. I'll keep you guys posted if my car starts to idle rough again. Oh and yeah, I also reset my ECU after i cleaned the MAF.

UTGS400

I don't have an intake on my GS and I have the same problem. They tried to tell me that I have a TC that is not working properly. I had Jeff at Bearden take a look at it and he said it is working fine. He also said that he believes there is a programming issue of some sort that needs to be addressed. His recommendation was to have everyone having the problem call corporate lexus and voice a complaint. If enough people do complain, they will fix the problem.

BTW, I edited my first post. Try to leave me a post with your idle info (w/ and w/o AC on) and what mods you have done that might effect the idle. In a few weeks, I am going to take a hard copy of this thread up to the dealership and get them to start working on the problem. I will also send copies of this link to both my local dealership and corporate lexus in hopes that someone will step up and solve this problem.

ChrisK

iTrader: (1)

My 95 SC400 is having this problem, exactly like Mr. Johnson described. I'm battling this problem for about 2 years without success. To give you a clue what I've done to try to solve this problem, and some others:

1. different MAF
2. different ECU, actually for 95 SC400 there are two different part numbers and I have them both
3. replaced EGR, idle speed control sensor, TPS, PCV
4. cleaned throttle body many times
5. checked for air leaks monthly
6. regular maintenance, spark plugs, wires, distributor cap and rotor

My 95 SC400 is stock. I can recreate Mr. Johnson case every time, cold or hot. When driving on AC car idles at 800 RPMs, when coming to stop or at stop turning the A/C off will cause the idle to go down to 200 RPMs and then climb back up to 500 RPMs. Car does not die during colder weather, but.when its hot it sometimes stalls while dropping to 200 RPMs.
I personally believe it is the ECU programming issue, and as you can see it is not only related to 98-00 GS400.

My 00 GS400 idles at about 500-550 RPM, but it doesn't die or vibrate, but I didn't have a chance to drive it in the hot weather. When humid 90F weather hits Chicago, I will definitely see if I can recreate this problem on GS.

jmecbr900

UTGS400,

There is no way that the TC can be the cause of "low idle". It's like saying the I stubbed my toe and it made my head hurt. One thing doesn't have to do with the other. The people that are saying that are typical mechanics that don't want to admit that either: A) they're stumped and don't know what is causing it. or B) Know what the cause is but don't want to fix it because it would cost THEM money.

All I'm saying is that it's so convinient for dealers all over the country to be blaming aftermarket parts for the problem even though the part they're blaming has nothing to do with the problem.

I had a similar problem with my Maxima. It started having problems starting. I took it to the dealer because I suspected an electronic problem (after 3 days of self diagnosing). When they opened the hood the very first time, the guy literally chocked and started blaming my direct port nitrous, intake, exhaust, etc.....NONE of which have anything to do with starting the car. They all work AFTER the car is started. I left the ignition, starter, battery, fuel injectors, and ecu stock, so therefore it has to be a regular problem. Well, after 2 weeks at the dealer and 2 "nissan Master techs" later, they were still chocking and blaming the nitrous because "it causes the cylinders to get fouled up with raw fuel because the spark plugs can't keep up" WAHHH?????

You know what I mean? Sometimes it takes running into a brick wall for some people to figure out that they can't just walk thru it. Lexus will eventually run out of things to blame it on and have to look at the ecu and/or TB combo. That's what logically makes the car idle the way it does.

UTGS400

I would agree to an extent. The mechanic was saying that the TC was causing my car to stall and at times idle rough. His reasoning does make sense (although I don't think it is my problem). If the TQ does not disengage properly, the car will stall. It is just like releasing the clutch of a standard with the break on. The car will first start to shake then if the RPMs drop too low, the car will stall. This does make perfect sense, but the problem is when a TQ goes out, it typically does not allow the car to move. In other words, it is not a problem with the TC engaging, but rather disengaging.

GSquicksilver

just wondering... did anybody here ever had their engine mounts replaced? cuz i just realized that on some honda vehicles, rough idle is due to worn engine mounts. just thought i'd point that out.

jmecbr900

I think that you're mistaking one thing with another. You don't have rough idle because of broken motor mounts. You have vibration because of broken motor mounts. The rough idle may cause vibration which is then felt more due to broken motor mounts......you get the picture.

jmecbr900

I follow the logic, except that's not what happens in an automatic tranny. The torque converter doesn't "engage or disengage", it is always on (spinning). It has to spin up to certain rpm's before it has enough fluid, force, etc to transfer power thru, but it doesn't stop working per se. I understand what he's trying to say. He should of probably said that the neutral switch or sensor is out of whack, but not the TC. It either works or it doesn't. Very seldom does it linger on in agony before dying. I know from experience of changing 3 just last year in my other car.

Either way, as you stated, it's not the cause. For one very simple reason.....there are completely stock cars doing the exact same thing as modded ones. Logic points to that fact showing it's not the modded parts making the difference. If it was that the car only did it at certain temps, under certain loads, under certain conditions, that would be one thing. I think I remember reading a ton of threads about this problem and it has no real predictable pattern except years of the car and model. It's happened to people in very different situations, but acting exactly the same way.

bitkahuna

iTrader: (20)

OK here's my data... I have the PI TC and I have an intake (K&N) without ECU.

The other day I specifically got the car warmed up got to a light and turned the AC off. The idle dropped to about 400rpm and it was SLIGHTLY rougher which is not surprising since that's a pretty low idle speed, but the tach stayed ROCK STEADY on 400rpm. If I put on the AC the idle went up to about 750rpm I believe and stayed there steady.

So basically I have NO idle problem with or without AC on and I have a TC and intake. One other thing, my K&N intake pipe is PLASTIC not steel. Maybe that helps me??

I have a 2000 GS and most of the problems I've heard about have been '98's and '99's.

And Mr Johnson, with all respect, your data is going to be different than most since you have a SUPERCHARGER, right?

Guitarman

No stalling, just rough idle. I just deal with it by either putting on my parking lights (during day) to create a load or feathering the gas pedal so it idles @ 600-700 RPM. With headlights on at night or A/C on , no problems at all.The parking light thing is fine, except for the fact you don't want to forget you left them on when you park.

I'm assuming the low idle problem is non-existent in cars with DRL'S??? Maybe I'll just wire my headlights that way, lol.