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srgilbert

Throttle Position Sensor

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I have been struggling with a jerking transmission when my 95 LS400 is up to speed and I take my foot on and off the accelerator. I had the dealership check the trans - said it was fine and saw no codes. Their thought was to first replace the plugs then the throttle position sensor and if all else failed the ECM. I replaced the plugs and am now at the TPS. DOes anyone have a procedure to adjust it as well as the correct voltages you should find?

THANKS

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im out of town rite now but tomorrow during pm hours i will give u that info from the factory manual. if some1 has gen II manual they might give it to you even earlier

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Certainly appreciate sharing the lexus service manual. I was told that you have to "tune in" the TPS and I have found Toyota specs for a V-6 but not the Lexus V8. Can I also ask there appears to be two sensors opposite the throttle cable - one is to what I believe to be the choke and the other seems to be closer to the engine and tied into the throttle plate. Can you confirm that the latter is the TPS? Unfortunately the replacement ND part looks exactly lik the other two and the part number has changed since the production date.

Thanks again

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first of all if your tsp is bad you should be getting one or few of the codes p0120, p0121,or for sub tsp - p01400,p01401.

CIRCUIT DESCRIPTION

The throttle position sensor is mounted in the throttle body and detects the throttle valve opening angle. When the throttle valve is fully closed, the IDL contacts in the throttle position sensor are on, so the voltage at the terminal IDL1 of the ECM becomes 0 V. At this time, a voltage of 0.3 ~ 0.8 V is applied to terminal VTA1 of the ECM. When the throttle valve is opened, the IDL contacts go off and thus the power source voltage of approx. 12 V in the ECM is applied to the terminal IDL1 of the ECM. The voltage applied to the terminal VTA1 of the ECM increases in proportion to the opening angle of the throttle valve and becomes 3.2 ~ 4.9 V when the throttle valve is fully opened. The ECM judges the vehicle driving conditions from these signals input from terminals VTA1 and IDL1, and uses them as one of the conditions for deciding the air-fuel ratio correction, power increase correction and fuel-cut control etc.

here is the description of the first error code

post-4-1076864411.gif

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and another one:)

this is only for the first error code, so check for codes first b4 making any repairs., i really think if your check engine or track lights are off everything is ok and problem is in smth else.

but check for codes anyway since sometimes codes might be in the ECM even with the lighs off.

post-4-1076864521.gif

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Wow - now I have more than I can possibly digest. Thanks. I have been told that a TPS can fail without throwing out codes. I'll report on this one the cahnge is made.

THANKS

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I had the same problem with my 95LS. Also mine would die after driving for long distances at highway speed then coming to a stop. It would then start right up and idle perfectly until I drove for long distance again at highway speed. The transmission problem went away with the replacement of the ecm. My 95 has 95000 miles and Lexus warranty covered repairs up to 80,000 miles. I then had to pay 1% for every 1,000 miles over. Total cost to me was 15% or $250.00. Lexus did not test drive my car because they said it would take to long to duplicate the problem. If you have to replace the ecm this might save you some $$.

:rolleyes:

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I had the same problem with my 95LS.  Also mine would die after driving for long distances at highway speed then coming to a stop.  It would then start right up and idle perfectly until I drove for long distance again at highway speed.  The transmission problem went away with the replacement of the ecm. My 95 has 95000 miles and Lexus warranty covered repairs up to 80,000 miles. I then had to pay 1% for every 1,000 miles over.  Total cost to me was 15% or $250.00.  Lexus did not test drive my car because they said it would take to long to duplicate the problem.  If you have to replace the ecm this might save you some $$.

:rolleyes:

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Wow - I dodn't know that Lexus would come through on a replacement ECM on a pro-rated basis. I have found a bone yard ECM for about $150 but I really did not want to go there. Can you share with us how you managed to get Lexus to come through on this one?

I had a similar problem with my 95 dying when coming to a stop after extended high speed. The problem was a dirty air filter - yea I should have known better.

Please let me know how you "worked" Lexus.

Thanks!

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Please refer to post by JOldaker dated 12/11/2003. You will find a reply by Pachocco1 that was very helpful to me. I simply advised the service mgr. of this service memo and he contacted Lexus HQ to see what they would do.

I have been trying to add this address to my replies to you but I must be doing something wrong because it dissappears everytime I attach it.

Good Luck

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TSIB

Introduction Early Production 1996 Model Year LS 400 vehicles may experience an engine idle speed

reduction just before stopping the vehicle after a continuous long drive. To correct this

condition, the ECM logic has been changed.

Early production 1996LS 400 with VINs before JT8BH22F3T00414045

Parts : Previous part- 89661-50302 New Part- 89661-50303 Part Name ECM

Warranty info

OPCODE DESCRIPTION TIME OPN T1 T2

895011 LS 400 Driveability Improvement 0.8 89661-50302 08 71

Warranty Coverage 4years or 50,000 Miles

This is what the Bulletin says

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TSIB

Introduction Early Production 1996 Model Year LS 400 vehicles may experience an engine idle speed

reduction just before stopping the vehicle after a continuous long drive. To correct this

condition, the ECM logic has been changed.

Early production 1996LS 400 with VINs before JT8BH22F3T00414045

Parts : Previous part- 89661-50302 New Part- 89661-50303 Part Name ECM

Warranty info

OPCODE (895011) DESCRIPTION (LS400 Driveablilty Improvement) TIME(0.8) OPN (89661-50302) T1(08) T2(71)

Warranty Coverage 4years or 50,000 Miles

I have learned that I cannot forward the address with this info on it however I believe I can send this info to you.

:cheers:

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Thank you very much for the advice. I replaced the plugs with new ND ones even though they had only 30K miles on them and the problem has not reappeared in the last couple of days. I'm not sure if I should replace the throttle position sensor since I picked it up from irontoad.com but if the problem comes back I'm headed to the dealer with some ammo.

Appreciate everyones help.

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If you are going there with some Ammo then as may just get a new car 2004, don't bother to think about ECM. I heard the 2004 enhance a lot of new features on it. ;)

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big50daddy - Have you had an opportunity to take your 95 LS400 on an extended drive after getting your new ECM installed last month? Has the new ECM solved your engine idle reduction/stall condition?

To any techies - (1) TSB EG002-97 refers to a logic change for the 1996 LS400. To help with big50daddy's 95 LS400, this revised 96 logic must have been incorporated into the ECM replacement part for 95 models, or are the ECM's for both model years the same? (2) Since some, but not all, 1995/early 1996 LS400's experienced the idle reduction problem, does this mean that installing a used ECM for one of those models might or might not cure the condition?

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Yes I have taken many long highway drives and this fixed the problem completely.

I also had the problem of rough shifting in and out of OD sometimes. This was fixed also. :cheers:

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I'M A BIT CONFUSED ON THIS ONE. THE LEXUS BULLETIN IS FOR 1996 HOWEVER YOU HAVE A 95. WHY WAS LEXUS WILLING TO WORK THIS FOR YOU? I'M AT THE POINT OF ECM REPLACEMENT AS NOTHING ELSE HAS SOLVED THE JERKY TRANSMISSION PROBLEM AND THE PRICE IS JUST REDICULOUS UNLESS YOU FIND ONE AT THE BONE YARD AND FIGURE OUT HOW TO REPROGRAM IT FOR THE KEY FOBS.

THANKS

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The service mgr was very nice and never questioned the fact that I have a 95. I believe this is a common problem and Lexus does not wany any trouble in the event of an accident.

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Thanks for the road test followup, big50daddy, and congratulations on the improvements!

Re: 1995 vs 1996 ECMs and drivability improvements...seems the problem of the rough transmission shifts was apparent to Lexus in the 1995 models, but maybe the connection to the idling-to-standstill wasn't made until the 1996 owners started reporting. Anyway, the TSB that applies to 1995 LS400 is recapped below.

Technical Service Bulletin EG003-96 October 7, 1996 (OPCODE EG5002 requires the ECU replacement, cruise control computer, and spark plug replacements as a set for the 1995 LS400).

LS400 DRIVABILITY IMPROVEMENT - To improve driving smoothness at speeds above 40 miles per hour, the following components have been changed.

Applies to all 1995 vehicles from JT8UF22E*S0O:

Old part / New part / Application

89661-50220 / 89661-50224 / ECM Fed. (veh prod 9410-9502)

89661-50221 / 89661-50224 / ECM Fed. (veh prod 9502-9507)

89661-50230 / 89661-50234 / ECM Cal. (veh prod 9410-9502)

89661-50231 / 89661-50234 / ECM Cal. (veh prod 9502-9507)

88240-50070 / 88240-50071 / Cruise Control Computer (veh prod 9410-9507)

90919-01180 / 90919-01178 / Spark Plugs (veh prod 9410-9507)

Thanks,

Lee

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Thanks for the road test followup, big50daddy, and congratulations on the improvements!

Re: 1995 vs 1996 ECMs and drivability improvements...seems the problem of the rough transmission shifts was apparent to Lexus in the 1995 models, but maybe the connection to the idling-to-standstill wasn't made until the 1996 owners started reporting.  Anyway, the TSB that applies to 1995 LS400 is recapped below.

Technical Service Bulletin EG003-96 October 7, 1996 (OPCODE EG5002 requires the ECU replacement, cruise control computer, and spark plug replacements as a set for the 1995 LS400).

LS400 DRIVABILITY IMPROVEMENT - To improve driving smoothness at speeds above 40 miles per hour, the following components have been changed.

Applies to all 1995 vehicles from JT8UF22E*S0O:

Old part / New part / Application

89661-50220 / 89661-50224 / ECM Fed. (veh prod 9410-9502)

89661-50221 / 89661-50224 / ECM Fed. (veh prod 9502-9507)

89661-50230 / 89661-50234 / ECM Cal. (veh prod 9410-9502)

89661-50231 / 89661-50234 / ECM Cal. (veh prod 9502-9507)

88240-50070 / 88240-50071 / Cruise Control Computer (veh prod 9410-9507)

90919-01180 / 90919-01178 / Spark Plugs (veh prod 9410-9507)

Thanks,

Lee

Lee, Thank you for the information on the 1995 Service Bulletin.

I just spoke to Lexus. The Service Rep that handled my repair said that he told the serivce mgr they should replace my cruise control computer and spark plugs as well. He said the serivce manager told him not to do it at that time.

:angry:

The service mgr is on vacation and will be calling me back when he returns.

The service rep also wanted to know where I heard about this.

:D

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Well, since your test drives have been trouble free, it is good to know that the ECM replacement by itself may cure both problems (downshifts/low idle).

By not discussing the set (ECM, cruise, plugs) with you before they performed the service, the Houston service manager has snatched "an unhappily surprised customer" :huh: from the jaws of "a delighted customer" :D .

Once a customer shows that he/she knows that TSB's exist, the dealers ought to just assume that the entire list will eventually surface, and talk through the options up front.

Anyway, good luck to the svc mgr :blushing: in your follow up discussion...

Lee

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Well, I may be able to provide some feedback on the 1995 ECU vs 1996 ECU questions. I've had occurrences of both 1995 problems - the low idle after high speed trips, and rough transmission shifts.

My 1995 LS400 is in the (non-Dealer) shop today for 90k service (spark plugs will be replaced, but cruise control computer will remain). I'm having ECU part number 89661-50303 put in to replace the 1995 ECU. The 50303 ECU is the part specified as New Part Number for early production 1996 LS400's in Technical Service Bulletin EG002-97 (introduction: 1996 vehicles may experience an engine idle speed reduction just before stopping the vehicle after a continuous long drive).

I'll post my test drive results (good or bad) over the next couple of days. If the 96 ECU in a 95 LS replacement works okay, I'll also post the site where I purchased the ECU $500-$600 range (w/12 month no-questions-asked return guarantee).

Lee

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Bad news -

The leap-frog experiment coughed up a bug. We hooked up the 1996 ECU 89661-50303 (specified replacement part for early 96 LS400's per TSB EG002-97) to my 95 LS400. We immediately got a check engine light - emission control system. Otherwise, a short test drive was flawless. We put the old ECM back, the check engine light cleared, and I'm returning the 50303 ECM.

(I noticed that the TSB for the 1996 LS didn't differentiate between national vs California vehicles, while the 1995 TSB did list both. So maybe the 96 ECM's got a "consolidated" calibration for the emissions system?)

Good news -

I walked through my experiment with Tracie at Our ECMS Company, Duryea PA, and today she is sending a replacement ECM 89661-50224 (specified replacement part for 95 LS400's per TSB EG003-96).

If you want to try this route for obtaining an ECM, you can reach Tracie at 1-877-687-3267 or email AUTOECMS@AOL.COM or visit www.autoecms.com.

Here's what I understand about their operation - they take in exchange units and reprogram them to the specified configuration (e.g. 89661-50220 or -50221 can be reprogrammed to be 89661-50224). The normal sequence is that when you order 50224, they use an exchangeable "core" already in their inventory, reprogram it and send it out. ECM cost is about $550 net ($650 less $100 back when you mail them your old ECM).

Worst case, I suppose, is that if no corresponding core units are in stock, they will take your old ECM for reprogramming and send it back to you. This can be done pretty fast, apparently.

NOTE: What you get from AUTOECMS is a black box ECM with a part number label, but without the original factory label. Since they're reprogramming the units, they remove the original labels.

Anyway, there's the followup. Good luck!

- Lee

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