Jfinlay

Hi, I'm not sure if there is an introductions thread, but I will do a quick intro here. My wife inherited a 1998 LS400 in 2004 and it has been relatively problem free and garage kept. It currently has 165K miles. A few weeks ago, it went into limp mode while driving with Check VSC. Codes showed a throttle control motor clutch malfunction. I replaced the throttle control motor with great instructions from here, but since then it has been showing P0120, throttle position sensor. I replaced both the throttle position sensor and the accelerator position sensor and no matter what the TPS values still show 0% and the P0120 is persistent. I pulled the ECU to get it tested and rebuilt. I started reading the reviews of the ECU rebuilders that google returned with LS400 ECU repair and got scared. Does anybody have any recommendations of recent trustworthy repair places? Most of the online reviews mostly mention horror stories. I have the ECU ready to package, but unsure of where to send it. BTW, do I need to send the two key fobs (minus keys) with the ECU given (if I have read accurately) that the key fobs are paired to the ECU?

This car is special to my wife, but we no longer have a local mechanic we trust, so I started down the path of fixing myself, whether that was prudent or not. I'm not aware of anybody with the test equipment to look at the ECU signaling like in one of the popular Youtube posts.

If there is a "tuner shop" in the Baltimore Annapolis area that could do the test and repair, that would be an added bonus.

Thanks in advance for any and all help.

aptoslexus

Did you check the integrity of the wiring between the ECU and the sensor?

bradland

I wouldn't rule it out completely but ECU issues (leaking capacitors) were solved at the factory before the 98 models were produced.
There's a good chance the ECU is fine.

Jfinlay

TPS value was always 0 after the motor switch. I worry that I damaged ECU during throttle motor swap. Prior to motor swap, TPS was registering. I tested continuity of the pigtail on the TPS and it was fine.

Jfinlay

I decided this is probably beyond my ability, so I put it back together. Can anyone recommend a fair Lexus diagnostician around Glen Burnie, Elkridge, Columbia, Annapolis, Crofton area of Maryland? I’m still just throwing the P0120 again and the car is in Check VSC limp mode.

aptoslexus

I'm curious what directions you followed in doing the swap. There's a calibration involved. Did you do it?

Jfinlay

When I tried the calibration, I could never get a TPS reading on the OBD other than 0. I followed the Lexus calibration procedure someone posted here.

Yamae

It seems to me that the problem is that the TPS is not driven by the throttle control motor. Before jumping to the ECU. I'd check voltages of all 4 pins of the TPS manually rotating the throttle plate. I worry that the throttle control motor or the TPS is not well aligned. I also would check the connector and the harness if those 2 were well aligned.

Sometimes something like this happens. Simply replacing the APPS or TPS does not always fix the problem. The person Mike needed to try another APPS. The first APPS was not OK to use for his tackling car.

Losiracer2

have you tried adding dielectric grease to the contacts of the connector? I had a throttle motor issue on my 99' when it had 147k and lubed up both sides of contacts in the connector and now its been trouble free for over 3 yrs now. Mostly it was happening when it was cold in the winter in michigan so below 25 degrees F in the early mornings or cold days.

Jfinlay

I bought a take off throttle body from eBay. Replaced and had a no code Check VSC with some kind of semi-limp mode, but it showed proper rpm’s, tps position etc on live data. I reseated the accelerator pos sensor cable and problem went away. I then test drove, all was well, so I decided to clean connectors with electronics cleaner, dried with canned air, and put on dielectric grease. All was well, so I put everything together and declared success. A few hours later, had wife test drive , immediately had check vsc and no codes. Did the reseats, cleanings, etc, no changes….

through different incarnations, car will occasionally show p1126 , throttle control motor, while in check vsc but it clears with OBD and doesn’t come back…I’m starting to wonder about connector integrity as I’ve had the throttle body off 7 or 8 times now. Accelerator pedal sensor connector wire catch has cracked on initial take off of throttle body, but connector had full integrity and rubber seal, but most recently, I’m not sure I can say that so I have a new connector coming. Could I be out of the woods as car has no codes, no check vsc, but I’m not sure I trust it yet to give it back to the wife yet. I want to let it sit and try here and there until I get the new accelerator connector in a few days.

Yamae

So your problem must be related to this now. As long as the clutch itself is OK, all you need to do is to fix the connector/wiring issue.

Losiracer2

I would also inspect the wiring very closely as that can get brittle and crack. When I did the dielectric grease addition, it was likely the first time the connector has ever been removed from the throttle body, maybe once back in 2008 to do the starter also.