RA40

iTrader: (6)

In that case the lack of testing ripple current would be a visual inspection of caps in the ECU. Given the nature of running problems and frequency we've had this cap fix, this would take one of the bucket list items out. How is the A/C functioning?

Magda

Hi All,
AC does not work reliably in this car. Sometimes it works and sometimes it does not. But last time I checked it seemed to work a bit.



I recently was busy with my other stuff, thus not too much car work... I am a bit afraid to drive it due to the fact that it kind of goes to 45mph without hitting gas pedal --> don't want to ruin brakes.

Just wanted to rule out simple things first... Also given my very limited mechanical experience, it is a learning experience thus be patient with me. Sometimes I need to read a lot before I do something.



Since my last post I did some simple tests:



1. replaced PCV valve --> no change




2. Checked if EGR valve itself responds to applied vacuum --> I connected vacuum pump to its top vacuum connection and applied vacuum. The valve opened and held vacuum, thus it looks like valve can be opened and closed by vacuum. See pictures below:




I made blocking plate from Coke can foil that i installed instead of regular metal seal, to rule out that the EGR valve stays stuck open. Blocking EGR didn't remove the fluctuating idle phenomenon, thus it looks like EGR is not the cause of it.





I made blocking plate from Coke can foil to rule out that the EGR valve stays stuck open.




I tested EGR valve when the car was off. Here no vacuum applied and the valve is closed.




I tested EGR valve when the car was off. Here when I applied vacuum to EGR valve the valve opened thus it works.




Opened EGR valve when the vacuum applied is shown in this picture.





3. I looked carefully on vacuum lines and didn't find any obvious vacuum leak.

4. I disconnected battery a few times and each time it relearns, it ends up fluctuating in Neutral or Park after 1 to 2 minutes. When the car is already wormed up it starts fluctuating nearly immediately once I turn the car on. It now fluctuates between 950 and 1300rpm in Park. I may decide to take it for a drive, but am a bit affraid about the car going too fast as brakes on 1st Gen LS400 are relatively small.


UPDATE WITH PICTURES FROM THE MOST RECENT WORK FROM BEFORE THIS THREAD:



Air Intake Chamber during cleaning from carbon deposits.




Throttle body (TB) was a nightmare to clean.




It was very dirty... I cleaned it scraping it before I used TB cleaner. If you use TB cleaner first, the dirt just sticks to the metal better...




EXCAVATION PROJECT: Air Intake Chamber during cleaning from carbon deposits. EGR little pipe was completely clogged!!! I thought it was solid metal rod at first... not a pipe.




EXCAVATION PROJECT: EGR/PCV inlet housing (not sure its name) was totally filled with carbon deposits,




EGR little pipe and Cold Start Injector after cleaning. Not 100% clean, but it was very difficult to get to this point. I put towels in to make sure dirt does not go into the engine...




clean at least




Distributor cap and rotor new (left) vs old(right)




Distributor cap and rotor new (left) vs old(right)
Old had cracks in plastic next to metal T-shaped part, which are visible in this pic.




Old distributor cap.




Visible cracks in plastic.




New rotor.



I also cleaned IAC (Idle Air Control) valve, because as you can see it was dirty.




IAC passage




IACV after cleaning.




I also inspected the bearings. Here the valve is in closed / extended position.




Here valve is in open (short) position.
Once I assembled the IAC valve, I tested it with 9v battery according to Lexus instructions. It was slowly moving back and forth in small increments.




I replaced PCV valve and grommet.




I changed valve cover gaskets and sparkplug seals. Also halfmoon seals and cam rear bearing cap with its plug. I used old bolts with new washer for valve cover gasket and for cam bearing caps...




Cam bearing caps, halfmoon plugs, old bolts with new washers.



I also replaced spark plugs and all its wires, triple checking the proper order and placement of wires.


TEMPORARY CONCLUSION:
I realize that all those repairs I did just before the problem appeared point to something I recently did. I still suspect a vacuum leak, but where is it...
Before repairs, the idle was really low, around 350-400 rpms... but there was no fluctuations. Now idle is around 900rpm and fluctuates between 950 and 1300rpm in Park or Neutral. Those fluctuations are very regular (every 1.5 or 2 seconds - I may record it to show you, but didnt get to it yet) and each time when 1300rpm is reached, I can hear an electric buzzing sound, engine shakes a bit to decrease rpm and rpms go down to 950 to repeat... like something wants to lower it back to 950rpm and something else is dragging it up.
In D (drive) it will gradually speed up by itself to 40-45mph without touching gas pedal. When in D on stop light, rpm will sit at around 900.

Maybe I cleaned something too well. By the way, I torqued everything to proper torque with beam torque wrenches or a clicker if beam wrench was too bulky for the particular spot...



I will gradually follow your suggestions. There is so many of them... I have some ideas and doubts.



Thought A. ECU capacitors must wait a bit. I have no soldering skills yet. I can use digital multimeter a bit... I have to learn more before I attempt that.



Question B. Checking timing with timing light is a bit mysterious to me. Is there a possibility that timing itself may cause my symptoms?


Question C. Coolant Temperature Sensor -I understand the idea behind it, but wouldn't it cause fluctuations that would be a bit unpredictable, as air bubbles would go through sensor in irregular way, causing computer to fluctuate idle in irregular way?



Question D. I installed new distributor caps and rotors, new wires (that were tested for resistance) and new sparkplugs (that were tested for proper gap). What would happen if one rotor was not installed correctly and got damaged... would it cause the car to not turn on at all or would it fluctuate in idle like mine does? I dont think this is it, but I didn't unscrew new distributor caps to inspect new rotors...

dicer

Wow nice job cleaning stuff, for the IAC what did you use? Almost looks new.

python

iTrader: (4)

good write up..great job cleaning,that tb was horrible

Nelexus88

I would say you are on the right track by suspecting a vacuum leak. The ECU closes the IAC valve trying to reduce the idle speed but the vacuum leak is too large for that to work. When the idle rpm reaches 1600 rpm the ECU temporarily cuts off the injectors to prevent over speed, then back on when the rpm drops to 1100. Thats what is causing the idle speed variation.

In order to find the vacuum leak, try spraying carb cleaner or something similar around the suspected vacuum leak areas, gaskets, hoses etc while the engine is running. The idle speed will change when the flamable vapor is drawn into the engine thru the leak. There may be Youtube videos of this test if you look.

RA40

iTrader: (6)

Good job Getting in there to clean all those high miles areas will eliminate later potential issues. My only suspicion at this stage is the ECU caps. Getting in there to get a visual is easy relative to what you've already accomplished. Then you'll know for sure the next step.

Magda

Hi,
I will probably take the ECU out at some point to take a picture and ask for advice this is unless I find the solution sooner. Summer time activities are slowing me down

Yamae

I happened had a chance to see the similar surging problem today at my local shop where I sometimes visit. It's a Toyota Crown which has a 1UZ-FE engine. The problem was caused by the vacuum leak at the gasket used at the intake manifold.

The shop owner quickly found the leaking point saying to me, "I'm good at these common old problems but not electronics affairs like someone".

2GenLS4

Upon cleaning the IAC valve did you also replace with new gaskets? I had a buddy with an integra having the exact same surging issue, we cleaned the throttle body and idle air valve and replaced, it ran fine for a few minutes and began surging again. We then repeated the process, this time I replaced the gaskets and ran a 1/3 of a Seafoam container through the throttle body to wash away any of the extra residue that may be collected and the surging stopped.
The resistance numbers you posted are roughly around average.
Another cause to my knowledge could be the ecu is tricked, and the car is running to lean causing it to idle up and down, but even in gear you would have a surging problem in this case until you are on te throttle.

Goodluck with fixing.

Magda

Fluctuating idle problem in lexus ls400 1990.
REVIVING this thread... Still wasn't able to track down the cause. But didn't do much since last post - I lost inspiration thus no posts for extended amount of time...

To remind you what was done just before problem appeared to be apparent:
- new Valve cover gaskets and rear plugs
- new spark plugs and new wires (tested wires resistance with multimeter)
- new distributors and new distributor caps
- cleaned egr pipe in air intake chamber
- cleaned cold start fuel injector in air intake chamber
- cleaned IAC valve
- removed and cleaned THROTTLE BODY, put new TB gasket, new little coolant hoses, new hose for PVC system under throttle body

After all that I started the car and the problem of fluctuating idle begun in N and P...
D, R, 2, L gears were at constant rpms when no gas pressed...


To troubleshoot:
-I checked vacuum lines, tried propane test with no luck.
-I rechecked IAC valve and tested with multimeter and all works within spec
-I installed new PVC valve and hose
-I used EGR blocking plate to rule out EGR valve. No change.
-I checked EGR with mityvac mv8000 vacuum pump. Within spec.

SINCE MY LAST POST I went for "vacation" from fixing my Lexus as it was upsetting that I could not figure it out...

-Recently I bought a new old THROTTLE BODY with new old TPS... I tested it with multimeter and its within spec. After installation it didn't help with the symptom. Thus I assume it was not TP nor TPS...

Currently after starting the car and keeping it in Park the rpms still do the same thing... RPMs are at first rising slowly to 1200rpms then start to fluctuate between 800 and 1200 rpm with rapid drop to 800 again in the interval of time that stays pretty much constant...
It can be seen on my YouTube links below:



If you have any suggestions please post.

Magda

2GenLS4: I didn't have to replace the gasket, as I did not take the whole IAC valve out. Just the part that was shown in pics. It does not have a gasket.
Thanks for your input.

Magda

Thanks for your response... isn't this intake manifold gasket a pain to replace?... Thanks for your input. I respect your expertise

Yamae

I found it's a time consuming job looking at the mechanic changing the gasket ordered by the owner. It was not completed while I was staying at the shop for about 2 hours. The mechanic once had an experience to replace the starter motor for a 1UZ-FE engine and he knew the most but he was saying I hate to do that.

dicer

I now have a similar problem, mine idles just fine when cold. After it heats up it does a surge and is running very rich, it started out of the clear blue. Visual check of caps looked okay and will do that at some point.
The thing about a problem when heating up is 2 things are happening that I can think of. One is the engine coolant temp sensor is supposed to say we are warm and lets back of that cold enrichment, and two its time for closed loop and let the O2 sensors take control.
Magda did you ever try seeing if there are any codes set? I'm not sure how fussy these are as far as the air meter mine did have that code, I had a really dirty air filter on that car. And its way down on my car project list so not sure when I'm going to fully dig into it.
Your doing good keep at it and if you figure it out please let us know what you find.
Your Norm light flashing means either the air ride is switched off or there is a fault code for that.

Magda

I've read that the starter is real pain to install. It's surrounded by the engine