Idrive70

Hi everyone,
EDIT: Updated post to reflect all that I've tried since original post.
Another update:
I see there have been over 2500 views of this post. So, obviously, this garnered interest and is likely an issues for other forum members.
I can only conclude the following to help others:
1) The ECU is/was the likely culprit causing the revving issue.
2) Although the ECU was rebuilt, I may not have "re-set" it properly. Someone told me that you must not only disconnect the
battery, but you must wait 20 minutes. THEN, with the positive connected, you must "tap" the negative post connector to the negative
battery post lightly a couple of times. He said that's the only real way to properly re-set the ECU. All I know is that I did this and it DID
make a difference. The revving stopped. The car ran like crap for several miles as the ECU was likely re-interpreting the new data while
I was driving. But, it worked!
3) I also made a very minor adjustment to the throttle cable because I found the idle to be a bit too low. I may have moved it the width
of a nickel, but that's all it took.
I hope this is helpful to someone else down the road.

For the past several months my SC 400 has a "weird" and inconsistent issue.
Please offer some feedback.
It will idle up/down/up/down repeatedly from about 500 rpm to about 1200 rpm when in park or neutral. If I drive it while this occurs, then with my foot on the brake and the car in "drive," it will idle over 1100 rpm and will feel like it "wants to take off." I have to hold the brake firmly. And, if I drive when this is occurs, then sometimes the car will coast WITHOUT me pressing the accelerator up to around 40 mph.
In addition, around 45 mph, the car makes a light "knocking" sound. Bascially, I have to drive just above or just below 45 mph or the car "seeks," like it wants to be above or below that speed. [Sorry, this is hard to explain].

These issues are entirely intermittent EXCEPT for the "seeking" at 45 mph. That's consistent.

It doesn't matter if it's cold outside or hot, rainy, dry, etc.
It may occur when I first start the car or may begin after driving half an hour.
It may show up for 5 minutes, disappear and start later that day.
It may show up for 10 minutes, and disappear for a week.

I read a few threads on the forum that suggested this can be due to the:
IACV, MAF or TPS.
To date, I have:

• taken apart and completely cleaned the throttle body
• removed and thoroughly cleaned the IACV
• swapped out the original IACV with one I pulled from a parts yard. [Cleaned this IACV, too].
• removed the MAF, cleaned it, put it back and this seemed to destroy the MAF.
• I replaced it with another used MAF and all seemed "normal," but idle issue remained
• disconnected the battery in order to "reset" the ECU multiple times
• Read the ECU board can have bad capacitors. The board was tested, some caps were bad. All caps were replaced with new. ECU was
  put back in car.
• seafoamed the car via the vacuum line--twice
• run Berryman fuel treatment through the gas tank twice
• run Lucas fuel treatement thought the gas tank a few times
• changed the fuel filter, once
• cleaned the air filter
• done a complete DIY tune up including rotors, caps, plugs, wires [plugs and wires twice!]
• Tried gas from several different gas stations
• Oh, and I had one ignition coil go bad, replaced it and recently replaced the second coil pack
• Did the fuel bypass mod suggested by many people here [so it operates at 12v all the time].

I welcome any input input. Thank you.
Does anyone have any ideas on what else to check?
For anyone else facing this issue, there are a few good links. This is one of the best ones:

http://us.lexusownersclub.com/forums...rk-or-neutral/

BeaksSC

iTrader: (1)

I guess just before anyone else says it, I will haha. Try to adjust your TPS sensor. I used an actual connector I cut off a junkyard 1uz and then used the multimeter right to the wires, but a lot of people use a custom made computer power cord that plugs in after you cut the side down a bit. if you search sc400 tps adjustment I'm positive you'll find a tutorial. I didn't have any up and down rpm's but as I was playing with mine, I know if it's turned counterclockwise it raises the idle rpm and vice vera when you turn it clockwise. It's very sensitive so it may take some time (number will jump from like .5 to 17 in a mm or less it seems lol). I'd try to adjusting that first since it's not an expensive adjustment it you have a multimeter handy. Good luck with the fix.

**I adjusted mine when I was trying to fix a misfire like issue. We think the problem ended up being the connector to the bottom ignition coil since it wouldn't sit normal and both the coils prongs were pushed in and the connector was strange looking. Replaced that and it seemed to be fixed. But that wasn't until after a lottt of trouble shooting. We think that was the issue, but then again we had a ignition coil wire destroyed by the cam gear, adjusted the tps, had the iacv off, and some other stuff.

phillup23

This is EXACTLY what I've been going through. Pleeeaaase lmk if and how you fixed it.

GISguy

Try a replacement ECU. Blown cap maybe

SirBoosty

iTrader: (1)

Had literally an identical problem on mine. After replacing the IACV, cleaning the MAF, changing plugs, wires, and distributor cap, I searched for a vacuum leak. Low and behold that's what it was. It takes 30 min of your time to trace each vacuum line to make sure none of them are cracked or torn. There's a vacuum line diagram on the hood of your car. Try that. If not a vacuum leak, check to make sure the TPS is within tolerance, and finally, do the ECU mod. If none of these fix the issues, it's probably the ECU.

ems

iTrader: (1)

My ls400 acted the same from a vac leak.

Idrive70

Thank you for all the replies!
I will be trying the fuel mod. Vac leaks make sense, too.
In addition, I did more reading and the ECU makes a lot of sense.
FYI for anyone else facing "weird" idling problems, the capacitors on the ECU can break down and leak.
This is a somewhat known issue with these cars.
FYI, links below:

http://www.clublexus.com/forums/ls40...acitor-66.html

https://www.clublexus.com/forums/ls4...-by-yamae.html

http://www.lexusownersclub.co.uk/for...ne-ecu-access/

SC400slide

iTrader: (11)

Rebuild your ECU. Probably needs it anyways.

t2d2

iTrader: (8)

And if it doesn't, it soon will.

phillup23

Vac leak wouldn't come and go. Should rule that out right? Also I replace my iacv and nothing happened so I ruled that out. Will try tps today. How does one do the fuel mod? Is it the 12v mod? And does anyone know of a place that'll rebuild my ecu for not so much. Cheapest I've seen is 150 with lifetime warranty. Probably gna jump at that. Thanks.

SC400slide

iTrader: (11)

$150 with the lifetime warranty is the best you're gonna get. Something else to keep in mind, unless I missed it somewhere, have you tested the o2 sensors?

phillup23

Yea. Guy is Atlanta. Going to contact him today. Also would sensor throw a cel on. My cel is not up. Also at start up smoke come out the exhaust. Smells like gas at time. Have a feeling its one of the 2 ecu

t2d2

iTrader: (8)

Well, it could be something less intuitive like a vacuum leak causing the IAC to hunt constantly. I would definitely start with the ECU, though, and hope that solves a variety of problems all at once.

phillup23

A moment ago took out my ecu. Found out from the guy that's going to rebuild it that its a 92-94 California ecu on a 95 sc. Gna see if he would want to swap for a 95 ecu he has ready. Wish me luck.

t2d2

iTrader: (8)

Mixing OBDI and OBDII, as well as CA emissions and non-CA, seems sure to cause problems! I'd be surprised if addressing that doesn't solve a few issues for you. I imagine your O2 sensor data is being misinterpreted by the ECU, if nothing else.