Ls400 Idle Loops Up And Down From 1100rpm To 1600rpm Every 3 Seconds

[Magda]

Hunting will be caused by the system trying to correct for something. Like too much air getting in and causing the idle to go up. Then the ecu says no, your supposed to be idling at this speed and corrects it.

With out a good way to check the various signals its going to be a hit and miss deal. When its cold does it do this or just when it warms up.

It does it when it's warm. It starts doing it approximately 1 to 1.5 minutes after turning cold engine on(cold after New York hot summer night...), but after 1 to 2 minutes of idling I don't think that the engine is fully warmed up..

[Magda]

Question E: By the way, I tested TPS but did not adjust it yet. Could TPS cause fluctuating idle in Park and Neutral?...

[sha4000]

I would be looking at the IAC and the throttle body cleanings. Those are the things that can change the idle the most unless yoyr timing is out of wack. Did you scrape the carbon build up with a screw driver out of the TB?

[Magda]

I would be looking at the IAC and the throttle body cleanings. Those are the things that can change the idle the most unless yoyr timing is out of wack. Did you scrape the carbon build up with a screw driver out of the TB?

I did scrape the carbon build-up from the TB gently with a screwdriver and with a blade I also used paper towels soaked with TB cleaner spray. I was careful not to damage the TPS by exposure to the cleaner... After I reinstalled TB I checked with multimeter if readings are within spec and they all were, including filler gauges of proper thickness (see one of the previous post). I probably created some scratches with those tools but the alternative was to leave it dirty as the carbon buildup was so bad that cleaning just with towels soaked with TB cleaner did not remove the dirt but solidify it more... I may consider TPS adjustment... I haven't done it yet as everything was within the spec.

For IACV I didn't have to use the screw driver or a blade. Just rubbing with tissue soaked with TB cleaner was enough. It was a lot of work and it took a long time as I took my time to do a good job... Insides of the IACV were not really dirty, thus I did not clean it. But disassembling allowed me to inspect the valve for functioning and moving valve in and out allowed for better cleanup.

[sha4000]

You seem to be real thorough with all your repairs. Sometimes those lil micro scratches can cause problems, that's why I asked. I'm somewhat stumped right now since your vouching for all the usual suspects. IACV, TPS, no leaks......

[Magda]

You seem to be real thorough with all your repairs. Sometimes those lil micro scratches can cause problems, that's why I asked. I'm somewhat stumped right now since your vouching for all the usual suspects. IACV, TPS, no leaks......

Craig, thanks for your response. I am not positive that IACV, TPS are 100% fine. I tested them with multimeter as described in this thread and both passed with flying colors. But i didn't test the connecting wires so I am not sure if all is fine... Also I tested for vacuum leaks, but it does not mean that I haven't missed one of those... I am puzzled and a bit tired, especially given that I am a newbie -I begun working on cars only last summer, mostly due to tight budget and partly because I like to fix things. My expertise in car fixing is not that great, but when I do something I try to educate myself extensively before even touching the problem / broken part. I may end up going to the mechanic, but am worried that he is going to just guess and throw parts at the problem, especially given that I'm just a girl...

[sha4000]

Your right to be wary of a mechanic if you don't trust him fully. Especially with OBD1 cars. Most are lost if they can't see a check engine light and can't plug a diagnostic tool up IMO. just keep at it and don't get discouraged.

[Magda]

OK. I will keep slowly at it. Mechanics don't have time to troubleshoot - they check the codes and throw parts and labor at problems until they solve them costly ;). I probably would do the same if I had to make a living out of it... Below are notes helping me organize my strategy...

Idea 1: Maybe I can disconnect IACV and remove the part that I so nicely cleaned out, then cover the hole with something (need to figure out what to use as a plug) and then see if it normalizes rpms in any way, probably making it really high?. Probably stupid idea.
By the way, is there anything in lexus that acts similar to Fast Idle Control Valve from Honda, as I read that Hondas have a problem very similar to mine...

Idea 2: find method to check Coolant Temperature Sensor... and make sure that my system does not have any bubbles... By the way, if it was the sensor or the bubbles, what would be the symptoms? and would they go away once the the engine got hot. Could any of it cause my symptoms?

Idea 3: adjust TPS with filler gauge and continuity to reduce the idle speed?...

Idea 4: adjust throttle body screw that is on dashpot, although I don't want to change it too much... (could that help in fluctuating idle?)

I'm rambling on a bit in order to get new ideas... I also want to evaluate all the ideas that I already got from all of you in order to get strategy that would allow me solve my problem with the least amount of trial and error lol . I cannot check everything at once... and each test requires me to study a new area of automotive knowledge and to buy new tools :( .

Idea 5: can i uncover throttle body inlet and then check what happens with IDLE? But what to do with the air hose from IACV and the little one connecting next to it that connect right after Air Flow Sensor...Would it be too much air for TB and intake chamber or too little? would it eliminate the function of IACV given the airhose from IACV connects right after air flow sensor? I apologize for possibility of wrong terms used here, as I don't know the names of all those parts...

Rambling on... hoping for the best...

[Exhaustgases]

If you spend the money on the tools you have something to show for the $.

[sha4000]

You sure that cam plug is sitting flush? What about the throttle body? Make sure the bolts are all torqued properly.

[sha4000]

And figure out where that buzzing sound is coming from,I bet that's the key to figuring this out.

[datarecovery]

Did you use the water bottle spray method to diagnose vacuum leaks?

Spray all intakes and hoses and any other possible leakage sites that come to mind.

That surging is almost always the IACV or a bad ECU.

The other thing that I modified in the past was the TPS , my car also had TRACS so it had dual sensors on the intake.

Lastly, cleaning the throttle body helped - all the Power Steering fluid sucked through a defective Power Steering Actuator valve had gummed up the throttle plates.

[Exhaustgases]

Did you use the water bottle spray method to diagnose vacuum leaks?

Spray all intakes and hoses and any other possible leakage sites that come to mind.

That surging is almost always the IACV or a bad ECU.

The other thing that I modified in the past was the TPS , my car also had TRACS so it had dual sensors on the intake.

Lastly, cleaning the throttle body helped - all the Power Steering fluid sucked through a defective Power Steering Actuator valve had gummed up the throttle plates.

And that Power steering fluid is Dexron automatic transmission fluid, you'd think it would help clean everything and not gum it up?

[Magda]

If you spend the money on the tools you have something to show for the $.

That's true.

[Magda]

You sure that cam plug is sitting flush? What about the throttle body? Make sure the bolts are all torqued properly.

I'm pretty sure it is sitting flush...

[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



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 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:

https://youtu.be/v9cDyYOeMtU

https://youtu.be/yhJf3pdnOIA

Thanks for all your help and ideas :)

[Exhaustgases]

I wonder if its okay to unplug the IAC valve, to see if it does affect it. Does it do it when cold and hot?

[Magda]

I wonder if its okay to unplug the IAC valve, to see if it does affect it. Does it do it when cold and hot?

That's a good point. A while ago I disconnected IACV /ISC valve CONNECTING WIRE to rule out that IACV/ISC is defective.

Then I turned the car on. The same behavior was observed.

The car idled with gradually increasing rpms from 1350 (when I started the engine) to 1500 rpms

which took approximately 40 seconds. Then It started to surge back and forth between 1100 and 1500 rpms in cycles...

It was a while ago when the rpms were reaching higher values.

Thus I concluded that neither the IACV valve (previous multimeter tests) nor its wire was the problem and there must be something else causing it... but what !

[landar]

You know, Magda, the problem is not nearly as bad as it used to be. If you look at your post #8, the pulsing was much worse than it is now, 900 - 1600 vs 100 - 1200. So, it appears that you have had some effect with your cleaning. If you take it for a drive now, I will bet that it does not 'pull' as much as it used to.

I wonder how the engine runs if you pull the throttle body ducting off so that just the throttle body butterfly is exposed. It should run but maybe not real well. Might be an interesting experiment. I would be tempted to manually move the butterfly to see if it can fully closed and if it operates smoothly.

[Magda]

You know, Magda, the problem is not nearly as bad as it used to be. If you look at your post #8, the pulsing was much worse than it is now, 900 - 1600 vs 100 - 1200. So, it appears that you have had some effect with your cleaning. If you take it for a drive now, I will bet that it does not 'pull' as much as it used to.

I wonder how the engine runs if you pull the throttle body ducting off so that just the throttle body butterfly is exposed. It should run but maybe not real well. Might be an interesting experiment. I would be tempted to manually move the butterfly to see if it can fully closed and if it operates smoothly.

Dear Randall,

Thank you for your message :)

It indeed got gradually better. I was driving the car from time to time since summer, but was not in the mood to continue fixing it -needed a break ;) thus I did not post anything...

My LS400 once started increases slowly and gradually in rpms until it reaches approx 1200 then it starts to fluctuate between 800 and 1200rpms every second or so when in P or N... in a very regular fashion. In D, R, 2, L it keeps at 600 rpm when no gas pressed. It still pulls and I feel that when I'm slowing down to stop the gears downshift with noticeable jerking of the car...

Recently even before installing "new old" throttle body I was driving the car quite often and there were no codes... at least the Check Engine Light was not lit. It used to fluctuate between 1200 and 1600 rpm in P and N - thus it looks like it is slightly better now. It does not pull forward like it used to but it still will not require pressing gas pedal to slowly reach high speed... Also it is pretty bad in terms of fuel economy.

No noticeable difference was observed in this behavior after replacing Old Clean Throttle Body to Ebay-bought cleaned "new-old " Throttle Body which was done this past week... (both throttle bodies had original sensors attached which I did not touch/adjust in any way)

However, for a little while now I noticed that my BATTERY GOES DEAD nearly overnight - it probably went bad due to problems from the past. For a year or two I had occasional battery going dead, but never thought about it too much as it was occuring once in a while... maybe i got used to it, sometimes I left dome light on. I eventually went through car records... I realized that alternator was replaced twice in this car by my housemate, within 2 years timeframe -I think mechanics didn't diagnose the problem and replaced alternator because it was good money.

2011 September : Alternator replaced

2012 January : Battery replaced at PepBoys

2013 June : Alternator and L/F Oxygen Sensor Replaced

Back then I was not interested in car mechanics. Now the battery is 3 years old on its deathbed. I begin to think that maybe there is a parasitic draw which would explain why it goes dead so often. Or maybe the CAPACITORS on ECU cause strange problems -can they discharge battery like that?

SIDE INVESTIGATION of BATTERY PARASITIC DRAIN :

Today I checked Voltage and Continuity on most fuses, while the smart battery charger (NOCO GENIUS G26000) was connected to battery leads to make sure that my bad battery allows for voltage to flow to expose parasitic draw if any (I try not to make too many mistakes, but am new to electrical diagnostics).

I used EXTECH true RMS multimeter.

I did not pull any fuses during that test.

The battery was connected.

I let the circuits go to sleep - the readings were done at least 5 hours after parking the car in the garage.

The results were negative: All checked fuses had continuity and there was no measurable voltage (mV) present across fuses... I also checked cartridge fuses under the hood - the same results.

[Cartridge fuses were tested in situ as well, after gently popping the top cap off with small screw driver. Basically I just touched meter leads to both sides of it up top with the cap off.]

Below are some pictures and explanation:

Kick panel / DASH FUSE PANEL fuses... All regular fuses showed 0mV and had continuity.

I could not access P/W, DEFOG nor DOOR cartridge fuses, thus I have not checked those... hope the power drain is not there. Not sure how to access them. Those 3 fuses described below:

* A P/W- 30 Amp: Preset Steering, Power Shoulder Anchor, Electric Moon Roof, Power Windows

* B DEFOG - 40 Amp: Rear Window Defogger

* C DOOR - 30 Amp : Theft Deterrent System, Seat Control System, Fuel Opener Control System

MAIN JUNCTION BLOCK / FUSES in ENGINE BAY.

I checked regular and cartridge fuses here. All checked fuses exhibited 0mV and good continuity.

The only fuse I did not check was cartridge fuse described as ALT 120A - I could not pop off the top...

*3 ALT - 120 Amp: Fog, Tail & Stoplights, Turn Signal Lights, Defogger & Seat Heater, A/C & Heater System, Power Shoulder Belt Anchorage, Door Lock Control, Power Windows & Power Seats, Antenna Motor, Cigarette Lighter, Combination Meter, Wiper & Washer

UPDATE 2015-Dec-11: I managed to pop gently the top of 3 ALT-120Amp Cartridge Fuse and checked it. It showed 0mV and continuity.

I also rechecked other fuses in Engine Bay/Main Junction Block -they again showed 0mV and continuity, apart from 7-DOME-10Amp fuse which had 2mV and continuity. I assume that 2mV is not enough to draw battery power.

RELAYS listed below I left alone:

* A - HEAD Headlight Control * B - ST Starter * C - ENGINE MAIN * D- MG CLT A/C Magnetic Clutch * E - HTR Heater Main * F - HORN* G - EFI Main

UPDATE 2012-12-12 12-12AM ;) :

This DOME fuse had 1.7 to 2mV, but it was the result of my MISTAKE: trunk was open during the test thus the light was on drawing

2mV... Once I closed the trunk it went down to 0mV...

To summarize:

I retested all fuses of MAIN JUNCTION BLOCK (including cartridge fuses) in engine bay - all had continuity and showed 0mV at Vdc. No blown fuses observed there.

I retested regular fuses of the DASH PANEL 0mV at Vdc and continuity was good. For some reason slot for RR.AC fuse was missing a fuse butI am not sure if it was supposed to be in my car.

Could not find at all 3 cartridge fuses of DASH PANEL that seem hidden: P/W, DEFOG, DOOR, thus they are not ruled out...

CONCLUSION: maybe my battery is just bad and does not hold charge...

schematic layout of Main Junction Block Fuse panel.

Measuring Voltage across Cartridge fuse.

Popping off top cover from cartridge fuse in order to check voltage and continuity.

That's all for now...

I post long posts as it helps me keeping track of all those troubleshooting. I apologize if it sounds like rambling on :) . It is potentially all connected and significant.

Feel free to comment by including number of post you refer to as my quoted post may be too long to be seen twice or n-times in a row ;)

[landar]

And of course, you have checked your trunk hinge wiring harness already. Right?

[Exhaustgases]

What is a quick check for that . Lights in the rear?

[Magda]

And of course, you have checked your trunk hinge wiring harness already. Right?

I always had taillight bulb blowing problem... I am attempting to check the trunk hinge wiring harness right now... But did not trace them yet. Just looking at it. Looks ok. Nothing obvious. I unclipped the clip. Will try to trace the wires but am a bit hesitant as i don't want to cause the problem.

I updated post # 45 -additional info under second picture regarding *3 ALT fuse... I checked it. It tested fine - 0mV and continuity.

[Exhaustgases]

Magda, don't give up on it. I've seen the pics of some of your work, your doing a great job. Even though its probably safe at the trunk hinge wire area, it is still best to disconnect the battery when fooling around the LS400 electrical stuff. You will be looking for a wire that is worn out from opening and closing the trunk lid. It could be obvious and it could be concealed with in the insulation of the wire too.

[Magda]

This DOME fuse from second picture of post #45 that had 1.7 to 2mV was a result of my
MISTAKE: trunk was open during the test thus the light was on drawing
2mV... Once I closed the trunk it went down to 0mV...

I updated the picture description accordingly...

To summarize:
I retested all fuses of MAIN JUNCTION BLOCK (including cartridge fuses) in engine bay - all had continuity and showed 0mV at Vdc. No blown fuses
observed.
I retested regular fuses of the DASH PANEL 0mV at Vdc and continuity was good. For some reason slot for RR.AC fuse was missing but
I am not sure if this fuse was supposed to be in my car.
Could not find at all 3 cartridge fuses of DASH PANEL that seem hidden: P/W, DEFOG, DOOR, thus they are not ruled out as potential culprits...

The battery may just be bad and not hold charge... I may buy new battery and try to take closer look into Trunk hinge wiring harness.