Magda

Thanks for this suggestion... I didn't clean MAF as I don't know how to clean this particular type. The MAF sensor spray cleaner from AutoZone/AdvancedAutoParts is for those other kind of sensors and LS400 1990 has FUJI sensor. I didn't search for the cleaning methods for it. I may try it.

Hi Landar, Thanks for the compliment ;) It is very encouraging. I was actually happy that the car started up after all those repairs ;) I know that Lexus LS400 drives itself in D without the need for pressing on gas pedal. I experienced this before my repairs when the idle oscillated around 300rpm (it was that low before my repairs). However, now when I am in Drive it really wants to go. I was on local roads where the speed limit is 20mph and had to constantly press on brake pedal lol Maybe because now the idle for drive is 900rpm ?... In post #6 I disconnected IACV wire, but left IACV valve attached to the car (not sure if it was in open or closed position). Then I turned the engine on and it was still looping high and low rpms... Thus I thought that IACV valve or its wire is probably not the reason for my problem. I can disconnect IACV again, and take it for a drive to see how it goes... Hope I will find the problem. I want my car back on the road ;)

Hi Landar, I took it for a spin according to your suggestion. Here is link to my YouTube Channel demonstrating what happens when I change gears. The engine was fully warmed up at the time of making this video (see coolant temperature dial): Observations: 1. Idle surges in PARK like stated before . The same behavior is in NEUTRAL (no pressing on gas pedal) 2. It does keep steady 900rpm in REVERSE, DRIVE, 2, L when the gas pedal is not pressed on. When I drive the car in DRIVE mode, I don't need to press on gas, I have to press on brakes... The car wants to go. I guess for some reason it wants to get to 1500rpm or something... By the way, this was my first big set of DIY repairs on Lexus LS400. I read a lot about vacuum system and all those components that I was working with. But I still am a newbie.... Thus bear with me if I'm not wording my posts 100% correct. I am expanding my mechanical vocabulary as we speak... I previously replaced radiator / fan / coolant flange / heater core on my Volkswagen MK3 Cabrio... I also did small tune-up before (spark plugs, air filter, MAF sensor cleaning). My automotive repair expertise is limited but substantial ;) And I always extensively research each and every new repair I'm thinking of doing myself.

I performed another test. 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 1000 to 1500 rpms which took approximately 40 seconds. Then idle started to surge back and forth between 1100 and 1500 rpms in cycles... Thus I conclude that neither the IACV valve nor its wire is the problem and there must be something else causing it... but what !

I've just found the video in this thread that actually shows nearly identical symptoms to my problem: http://www.clublexus.com/forums/ls400/700910-92-ls-400-idle-surging-help-please.html The above thread suggests that my problem could be IACV valve. I removed and cleaned IACV as well as checked its function with multimeter and battery as explained in post number 1 of my thread. Thus I am pretty confident that IACV is in working condition. Maybe its connecting cable?...

Dear Landar, Thanks for your suggestions. I checked the engine codes using hairpin wire method and found no engine codes. It may be because the engine got battery reconnected after a long time and I didn't really drive the car after that. I rechecked connectors and vacuum lines. I turned the car on in the morning. I kept it in P (park) and let it idle. At first the car was at 1000rpm and was steadily but slowly increasing in rpms. After approximately 80 seconds it reached 1500 rpms and then it begun its cycle of idle from 1100rpms to 1500rpms every 2 to 3 seconds... over and over again. It would drop to 1100rpms then increase to 1500rpms, when it would make a buzzing electrical sound in the engine bay and then it would drop to 1100rpm... and repeat again... After cycling like that for 2 minutes I turned the car off... It is very frustrating. I wonder what this buzzing sound could be? Is there any possibility that new distributor rotor and distributor cap may cause symptoms like that? Maybe cleaning EGR valve unblocked some vacuum lines in a strange way? Maybe IACV cleaning unblocked something? Maybe cleaning and unblocking 3 clogged vacuum holes which are at the top of throttle body, where the throttle plate rests in closed position. I will probably check throttle position sensor next, however I don't want to mess up any more components... Regards and Thanks!!!

Hi Craig, RH side cam plug is in a very inaccessible place and no space for mirror there. But will check in a while if valve cover / cam plug leaks are fixed. I may try to get smaller mirror to monitor the situation. I have another problem with the car now, which LS400 developed after a series of bundled repairs... LS400 idle loops up and down from 1100rpm to 1600rpm every 3 seconds. I created a new post for that. http://us.lexusownersclub.com/forums/topic/86818-ls400-idle-loops-up-and-down-from-1100rpm-to-1600rpm-every-3-seconds/

LS400 idle loops up and down from 1100rpm to 1600rpm every 3 seconds My 1990 LS400 runs high but even idle for approximately 15 seconds upon cold start. But then there is a moment when it changes... The idle goes up and down in a loop from 1100rpm gradually to 1600rpm then sharply drops back to 1100rpm every 2 or 3 seconds. When idle reaches 1600rpm the car makes subtle electric buzzing sound and idle goes sharply down to 1100 rpm... And it does it over and over again... Below is a recap of repairs/maintenance I've just completed in my car: I did clean following components from CARBON DEPOSITS: 1. throttle body (removed the TB to clean plates and interior), 2. EGR VALVE 3. air intake chamber including COLD START INJECTOR and EGR little pipe above cold start injector (which is inside the air intake chamber and can be seen from TB inlet), 4. IACV valve ( I also tested the IACV function with 9v battery -see below). All those components were super dirty with CARBON DEPOSITS accumulated across the span of 25 years... Throttle body plate had approximately 2mm or 1/8 inch of deposit... The EGR little pipe that was supposed to be hollow was completely clogged with carbon thus I assume that EGR valve air passage to air intake chamber was completely blocked. At the same time I replaced following components: 1. spark plugs and ignition wires, 2. distributor cap and distributor rotor. 3. valve cover gaskets and rear camshaft housing plugs in LH and RH valve covers. 4. I cleaned and reinstalled PCV valve and replaced PCV hoses for PCV valve (LH) and throttle body (RH). The problem began after completion of all those repairs... I turned the car back. It turned on. It run high idle for approximately 15 seconds. But then there was a moment when it changed... The idle RPM went up and down in a loop from 1100rpm to 1600rpm every 2 or 3 seconds. When idle reached 1600rpm the car ma subtle electric buzzing sound and idle went down to 1100 rpm... I checked vacuum hoses and all seem to be connected. Now, I thought that the IACV / ISC valve which I cleaned might be a culprit, so I took it out and TESTED it according to instructions I found: The protocol for testing that I used (may be for ES300, not sure...) : "1. INSPECT VALVE RESISTANCE Using an ohmmeter, measure the resistance between the terminals (B1–S1 and S3, B2–S2 and S4). Resistance: 30–50 If resistance is not as specified, replace the IAC valve. 2. INSPECT IAC VALVE OPERATION (a) Apply battery voltage to terminal B1 and B2, and while repeately grounding S1–S2–S3–S4–S1 in sequence, check that the valve moves toward the closed position. ( B) Apply battery voltage to terminal B1 and B2, and while repeately grounding S4–S3–S2–S1–S4 in sequence, check that the valve moves toward the open position. If operation is not as specified, replace the IAC valve assembly" Resistance of IACV was approximately 25 ohms. The battery test worked as the valve was moving according to the book when the voltage was applied to B1-B2 and S1–S2–S3–S4–S1 or S4–S3–S2–S1–S4 grounding sequence was implemented. My resistance was 25 ohms but I found another instructions that said anything between 10 and 30 Ohms should be fine... I assume that IACV is fine. I reinstalled it... I reinstalled IACV valve. Reconnected everything. Started the car up. But the IDLE LOOP is still a problem... Please, help with your suggestions :) Thanks! What could cause a behaviour like that?

I placed the plug in its place in cylinder head. Didn't manage to press it all the way in, but pressed it down as much as I could. Then I put the cam bearing cap on plug and cylinder head. Then I bolted to the required torque. I hope the torque pressed the plug in its place. The valve cover gasket was also done at the same time. Only time will tell if those oil leaks were eliminated. ;) Will post the update in a while. Thanks for all your help!!!!

Hi All, I do this job slowly as I have other things in life apart from car repairs ;) so please, bear with me! LOL I have bent the RH metal bracket. Then I removed the bearing cap and its plug. I am now ready to reinstall rear camshaft housing plugs on LH and RH sides. I removed old FIPG (which was milky/yellowish) in color) cleaned surfaces with alcohol.The only doubt is that the rear camshaft housing plug (metal plug covered with rubber) is a bit bigger than the space I'm putting it in. I tried to push it down in its slot in the end of cylinder head, but it feels like it does not go all the way through. I don't want to use FIPG on the plug as the manual/protocol does not mention it at all. I even found on some other forum that the plug should not be sealed with FIPG. However, some people use FIPG on the plug itself... I plan to put rear cam plug in its spot on cylinder head even though it will not be pushed all the way. Then I will put FIPG only in proper place on cam bearing cap surface that meets cylinder head. I will then put bearing cap on top of cylinder head and a plug. I hope torquing the 2x10mm bolts on bearing cap will push the PLUG in so that it creates a proper seal... Let me know if my thinking here is correct. There is not a lot of info on the plug in terms of proper installation technique. Regards and thanks again.

I put plastic wrap over exposed cylinder head and over wire brackets to reduce the danger of contamination for whatever is exposed while valve covers are out. Here are some pics of inaccessible wire bracket blocking access to bolts of cam bearing cap on RH side (passenger). Inaccessibility is the reason why pictures are not that great.

My instructions also say that FIPG should be placed on certain surfaces of bearing caps as well as on corners of valve cover gaskets and over half moon plugs... PROGRESS UPDATE: The valve covers are currently off on LH (driver) and RH (passenger) sides... LH valve cover was relatively easy to remove. RH valve cover was a pain to remove due to a huge wiring harness running above the entire rear of passenger side cylinder/valve covers. --> Any tips on that? I'm worried that it will be difficult to put RH valve cover with a new gasket back in smoothly, without messing up the gasket placement. This wire bracket is huge and wrapped with old, cracked, peeling off remnants of what was an electrical tape 25 years ago... Some of it will definitely end up falling into the exposed cylinder head... My Lexus LS400 1990 has stupid metal brackets behind cam housing plugs on LH and RH sides. On LH side it is held by one very inconveniently located 10mm bolt. I managed to get it off in order to have more space to play with cam bearing and its 2x10mm bolts. At this point LH cam bearing is off as well, like I previously reported. However, on RH side the metal bracket , which blocks 2x10mm cam bearing cap bolts is held by 2 bolts in the back of cylinder head facing firewall, both bolts for this bracket seem impossible to unscrew... especially one of them. --> Does anyone have any idea what to do to unscrew this stupid RH bracket behind rear cam housing plug? I really want to replace both plugs... but I may be unable to, which is not the end of the world. I can live with oil leaks. Maybe no one knows how to replace RH cam plug because it is impossible and no one does it. lol!!!! Thanks for suggestions / solutions :)

I thought about it a bit. Under the front bearing cap I have a very old Cam Seal that may be leaking... If i take the bearing cap off now to reseal it with FIPG, I risk creating big leak in old Cam Seal... I do not plan to replace cam seal now. Thus it probably is not a good idea to move front cam bearing... If bearing leaks really bad in the future, I will redo the valve cover gasket and get to it when new seal is in... not sure what is the best way. Regards and thanks everyone for all helpful and well thought out responses :)

Interesting... In such case I may attempt to seal front cam bearing caps without doing the cam seal... This way my valve cover gasket job may be more complete... Valve clearances are probably too advanced for me.

I managed to remove the LH rear bearing cap by placing wooden stick on the bearing and tapping wooden stick with a hammer / mallet. I tried to be gentle. It helped to tap the front edge of the bearing directing the tapping towards the rear / firewall... I tried to be gentle. I first tapped on the sides with bolt holes but it didn't seem to work... I was thinking of doing cam seals as well... But I'm not planning to do the timing belt now thus cam seals will have to wait. However, do you think I shoud remove the front cam bearing caps (=the ones close to the timing belt) to reseal them with FIPG, even though I'm not doing the cam seals? Valve covers are out and I want to reseal with FIPG as much as possible without doing any damage. The Repair guide says that RH I6 front bearing cap determines the thrust portion of the camshaft. The same applies for LH I1 front bearing cap. Would I change the thrust by removing and resealing them? Any ideas?

Thank you Bob, I actually forgot to mention that I removed the bracket held by small bolt in the back. Otherwise I wouldn't have enough space to unbolt two bolts holding the bearing cap. The cam bearing cap is still stuck as of now.

Thank you, Denny. I love my ls400. It really is an amazing car. Offers smooth, relaxing ride with the power of v8 when you need it. It's 25 years old and still pretty reliable and very quiet ride. Will try to keep it on the road as long as possible. :) Regards :)

Hello Landar, I secretly hoped you would be the one answering my post ;) I value your expertise! Thanks for taking your time. Will try your suggestions. I didn't expect the bearing cap to be so stuck... It's hard to say for sure if it was leaking oil back there. I had a lot of oil grime around the entire edge all around the valve cover gaskets. Oil grime was also all around rear camshaft housing plug and its bearing cap, including the contact of bearing cap with cylinder head. My thinking was: the car is 25 years old. I am doing valve cover gasket anyways which probably has never been redone on this car. Half moon plugs and camshaft housing plug thus should be done while I'm in there. Now, that I have unbolted those two bolts and already tried to wiggle it, I feel I have no choice but to replace the camshaft housing plug as I might have created leaky surface by trying to detach the bearing. I will keep you posted. Thanks again!!!

HELP! Stuck camshaft bearing cap prevents me from replacing camshaft housing plug. Hello, Lexusarians I am new to this forum. Reading your posts helped me a lot in the past. I have a 1st Generation LS400 1990 with approximately 300,000 miles and counting. I am currently replacing valve cover gaskets as there was a lot of grime all around it for a few years now. LH (driver’s side) VALVE COVER is currently off the CYLINDER HEAD. MY PROBLEM: I plan to remove and replace CAMSHAFT HOUSING PLUG, which is located in the rear on the firewall side of cylinder head. The plug is covered with BEARING CAP labeled I6. Bearing cap is held with 2 bolts. I removed those two bolts and thought I would be able to pick the bearing cap up to gain access to the rear CAMSHAFT HOUSING PLUG. Unfortunately for some reason the BEARING CAP seems stuck. I don’t want to use too much force on aluminum and am hesitant using metal tools to pry the bearing cap off. One try was to insert the bolts into the holes using them to wiggle the cap off, but it didn't wiggle out at all... I'm thinking of some kind of a spreader? but the space is limited and I cannot seem to find a proper tool. Do you have any suggestions? What should I do? Not too much space there. Regards and thanks! Below are some pics. By the way: I also removed HALF MOON PLUGS made of metal sitting flush on the cylinder head surface edge. Space filled by one of them is visible on some pics. Interesting tip which helped me remove those HALF MOONS: take a piece of wood like a short wooden stick, place it on one side of half moon and then hit the piece of wood gently with a hammer/rubber mallet so the half moon breaks the seal and starts moving in a round fashion. Once it has moved a bit you can take it out with your hand.