micadevcon

Alright, installed the O2 sensors. No change. Dang. But, I decided to go right back to square one. I put the old Bosch Platinum 4+ plugs back in the car. Guess what? The car idles like a dream. BUT, now she has no power. Feels like its running on four cylinders. Acceleration is smooth if I barely touch or ease on the gas, but any sudden or sufficient [think passing or hwy on-ramp] causes it to rumble and rev w/o power. Most cases this indicated a plugged cat con, but this car accelerated fine, even excessively with the NGK Iridium IX plugs I had in there, but now, with the plugs the car came with, its fine. So the cats cant be bad? Is it possible the NGK's I got were just... bad? Going to scope the plugs and see whats going on...

Did you get OEM sensors? What is the part number? And generally, is there a good place to get varous part numbers for this car ((91) LS400)? I got Denso 234-4211 [says TOYOTA on them] off a decent-looking seller on eBay, new. Looks identical to the old broken ones I took off and replaced with Bosch. As for part numbers, unfortunately there isnt one single place that I have found to get that info. The service manual helps a little, but its not a list or anything.

Well, got frustrated not finding the union bolt for the fuel pressure test, so my father and I decided to make our own. We took a single union bolt from a junkyard fuel rail off a 1UZFE, drilled the top out, tapped it with 1/4" npt fitting to 1/8" fitting for our fuel pressure gauge. Got it all fitted together, tightened up and solid. Put in on the end union next to the pulsation dampner and attached our gauge. Started the engine up per the tech manual, 35 psi. Disconnected regulator, 44psi. Fuel pump works great, so that is not my issue. I have verified that my Fuel pressure VSV is broken, no continuity and does not switch to high pressure above idle. But I have confirmed that the VSV not switching isnt causing the problem, as I disconnected the vacuum line, plugged it, and test drove it, still same symptoms. So, I'll find a VSV to replace it, but the change it makes isnt enough to be causing my idle problems. O2 Sensors still havent arrived, anxious to get them! :D Will update after they are installed...

300zee, Thats great that the fuel pump fixed your issue! I will be stopping by St. Paul next weekend, and if my O2 sensors dont fix the issue, I just might arrange to stop in. I do recall hearing odd noises from the back of the car [fuel pump presumably] when turning. Plus when shes idling rough theres alot of clicking from the passenger side - I'm thinking either the ECU is making adjustments mad fast or something to do with the fuel pump relay. Just another possibility. About the basics, yeah, I hear you. For me it was hard to grasp the basics on this car at first, not really understanding how it all worked together, but now have a much clearer view on its operations! And thanks oldskewel, that helps alot as well - experience pays off in the long run. And I hope to continue gathering it! O2's should be in any day now...

The closest Lexus Dealership is 2 hours away and I simply cannot be without my car for god knows how long. Not to mention I really cant afford paying enormous hourly rates and ending up paying gigantic OEM part fees. NO sir, not when a stinking MAF is $1700, an ECU is $1350, and an IAC is $700. I can only imagine what the hourly rate is. And please dont bugger me on "You shouldnt buy a Lexus if you cant afford to fix things." This is a Lexus. Things arent supposed to need fixing so much. Ive owned three fords, a dodge, and a volkswagen with less problems. (most of those cars OLDER than this one) I saved up (Yes, $3000 is alot to a young adult NOT making $50,000+ a year) and bought this car for its "reliability", assuming its 'quirks' were easily fixable. How wrong I was. But I am keeping up hope. If I had a dealership nearby and they could tell me what is wrong in an hour or two or labor, I'd do it. But that isnt my situation, so I have to do what I can. I like to work on my own cars and throwing money at a dealership for a car 17 years old doesnt help me down the line when something else goes wrong or needs fixing. Experience is a great teacher and I wouldnt trade this time learning how every part of my car works for spending thousands at a dealership. And if this forum is going to be all "Take it to a dealership" then very well, I'll figure this out on my own. I just thought that others might be interested in fixing similar problems instead of throwing in the towel. If the opportunity presents, yes, I would like to take this car to a Lexus tech - but I dont have that convenience.

Fuel pressure is still a slight possibility, still wouldnt explain how she runs perfectly with a manually adjusted IAC, or when cold... If the O2s dont do it then thats the next step. I havent been able to test fuel pressure because of the odd fittings used [banjo-style with center-drilled bolts], which I cant find the dual-hole bolt that you can put two fittings on anywhere to test with, as you are aware of... I've put in about $1000 in parts, but there were some other parts not related to this issue that needed replacing [HVAC Control, Alternator, Hood Struts, Idler Pulley, etc]. And a few were related and needed to be replaced [Fuel Pressure regulator was completely blown, replacing O2 sensors did fix TRAC light error]. I didnt go with brand new parts, or my cost would be easily 10x as much. I got some salvage parts, others on ebay, and local shops - and the vast majority of the parts I replaced were tested first, to the best of my knowledge - which wasnt much at first! ;) But I made sure the replacement parts were good quality too, proper ohms, etc. And I didnt skimp on the criticals [rotors, finally got OEM wires, got best plugs, toyota fluids]. After a shop tossed out my IAC hose [split], I had to make my own with regular hose. Being unformed, Its squeezable, so when it started to stumble at idle, I disconnected the IAC so it couldnt compensate, and squeezed the hose a bit, and she started to die! This tells me that it isnt a lean problem, as if it were leaking elsewhere, reducing the airflow through the IAC should even it out - and it didnt. MORE airflow is needed. Thats why, when I adjusted the IAC myself - full open - and started it up. while it wouldnt start the first few times, once it held, it idled PERFECTLY, but slowly restored itself to poor running condition. This tells me that its sensor-related, as something is telling it to close erroneously, past the point of it running smooth. So, the O2 sensors have to be giving it some erroneous or confusing [hash] signals. Otherwise wouldnt it see that it is running perfectly and stay there with the IAC? I have checked and re-checked, and she isnt giving me any codes.

It could very well be the plug. Mine originally had Bosch Platinum +4's, and ran okay, but ran better with NGK Iridiums. Try swapping the plug wire with the corresponding cable on the other side of the engine, and disconnect again to see if it fixes, and that may tell you if its the wire or not. On the topic of mine, I think I have come full circle. When I got the car the first thing I changed was plugs and wires - one wire was severed! Engine still ran oddly - but wasnt shaking as bad as it is now. But I do recall that in troubleshooting a TRAC light, I replaced the O2 sensors with Bosch universal O2 sensors... And then she started idling rougher - I didnt make the connection at first. So, combining the IAC adjusting itself past perfect mixture and temperature-related, it must be a sensor problem. And per http://www.babcox.com/editorial/ic/ic10044.htm, Bosch O2 sensors produce more hash than Japanese sensors, which could very well be confusing the ECU on this poor '91. I have ordered a couple of Denso O2 sensors to put in, and will let you all know what happens.

I've done a full seafoam cleaning, cleaned out the throttle body and egr system. It cant be fuel related as the car runs great when its (been) cold (for a long time). My idea now is that there is a gasket somewhere, intake or otherwise, that due to heat expansion of the engine, starts to leak when the car warms up. Anybody else had similar problems? Leaking intake manifold gasket after warming up?

Already replaced MAF, Coils are good, tested against a new coil, no change. Spark plugs are good, there has been a problem with condensation buildup [NOT coolant] in the #8 cyl plugwell, cleaned that out but no change. And if it were those things, why would it run fine when its first started cold?

Okay, update time. I know its an old topic but I'm still unable to find the source of the problem. I had the fuel filter replaced - it was rusted on pretty good and my theory was that gunk inside settled when it sat for a while, and after running a bit would clog the filter up, blocking flow. Crappy theory and new filter didnt resolve the problems. Got fed up and took the car to a shop to get some diagnostics done. They saw vacuum leaks at the hose from ISCV to the intake and at the EGR. I put a new gasket on the EGR, to no effect. Will replace the hose next. PCV hose is cracked and will be replaced as well - might have been what the tech's saw during their smoke test. Checked the trunk harness, didnt seem to have any shorts? Left wires hanging as advised in the pertinent posting. Checked the coolant temp sensor [one by the fuel pressure regulator] and it came up ok. Other ideas: Could the intake manifold gasket be worn out? Engine is great cold but deteriorates when warmed up - possibly the gasket expands and leaks then? Also going to take a look at the TPS, as I am experiencing the hard-throttle, slow and jerky acceleration vs light throttle and good-smooth acceleration. Flooring the gas pedal results in hesitation and [what feels like] severe misfire vibration with slow increase in RPM. Lifting off on the throttle results in a sudden spike of power or at least faster, smoother acceleration. My last idea is the ECU...?

Seems the IACV can be ruled out... I pulled the IACV off, cleaned it with some carb cleaner and really inspected it. Nothing looked too bad. Only issue I could find was that the coil resistances were low, about 22.5-25 ohms. Spec is 30-50 ohms. So I manually closed the valve all the way, reinstalled and tried starting. It Died. And a second time. So... looks like the ECU doesnt have knowlege of the position of the valve at all times, its a 'reference' thing. After starting it again with my foot on the throttle, I let off and it fell to... 600rpm! Smooth and steady! It stayed that way for quite a few minutes! It has never idled that smoothly, I had to double-take as I couldnt hear it or feel it, so THATS how a Lexus should be! :D Only problem: With more time or as the car is driven, the valve seems to progressively open (or close?) more and more, causing it to run lean (or starve?) and sputter at idle. I thought that perhaps the low ohms were causing the valve to move in ways the ECU couldnt compensate. So I ordered a replacement. Got an IACV from a SC400, same engine, only difference is in the intake hose diameter and configuration of the valve tip- but otherwise the same. Coil resistances were 45 ohms, so dead on! After installing it I started it (did not manually close the valve this time, though) and she ran rough as usual. I am really at a loss here, when I manually closed the valve, it ran perfectly for a little while, and gradually got worse from there. It tries really hard to stay at 600, but dies down and surges up, bouncing around 600 rpm. Hitting the throttle smoothes it all out... till it starts idling again... I will next check out the TPS as Harky pointed out - perhaps it isnt getting the right signals for idle. Also doesnt seem to be any wiring issues on the trunk harness...

Nope, still trying to figure it out. EGR pipe doesnt seem to be the issue. I checked the EGR, cleaned carbon off, soaked in Seafoam, no change. I did notice what could be a slow leak, VERY slow leak, when I had the fluid in the egr valve, but nothing drastic enough to cause these issues. My next item to check is the IACV, which lends credence as the problem starts out slowly, as the car warms up, and stumbling starts in 'ticks' - progressing to stumbling and rough idle.

I would love to know how you reached the fifth bolt! Unless the 95 is slightly differently arranged, there were all sort of tubing blocking access from above, and next to no room to reach even halfway up from the bottom. My hands must be too big. :(

Search: egr pipe That would be more effective if there wasnt a 3-letter limitation in the searchbox! Anyways. For my 91, I was quoted the following: EGR pipe 25601-50010---$132.66 Gasket 25634-50010---$4.07 Gasket 25628-50010---$0.91 ..from this site: http://parts.irontoad.com/l_ord.htm So the pipe and two gaskets, one where it attaches to the intake manifold and one where it attaches to the exhaust pipe. From my labor and personal experience attempting the fix, it is a very intensive repair. Lexus usually drops the transmission to get to the pipe, yet some have done it themselves. I personally cannot see how it is possible without dropping the transmission. Thats why the cost from lexus is so high, its 8 or so hours of labor, plus parts. For the vibration, if its simply a vibration, without the engine running rough or acting strangely, I would look into motor/transmission mounts first. As for the acceleration, due to gearing it is fairly slow off the line, but the torque really hits as the rpms get higher, hence the delay. If it is an abnormal slowness for you, check the catalytic converters. If they are clogged, that would cause poor low-end power.

Just an update, I am continuing to have the same issues. Replaced injectors, no change. I ordered and installed OEM Ignition Wires, just to be sure (Had Autozone "Duralast" wires in it) and that didnt resolve the issue. I didnt think it would anyway. I am back to wondering if this is all an EGR/Pipe issue. When the car has sit for a long time (8+ hours) and is started, idle is smooth. While the car warms up, the idle begins to drop, ever so slowly. Around 500 rpm there starts a strong vibration in the cabin, and soon the misfiring starts. First a single misfire, a few seconds pass, and two more, and gradually the misfiring becomes constant. When revved, it goes away. Most of the time I have to put it in neutral at stop lights because the whole car jerks and shakes if its kept in drive. This seems consistent with a lean misfire, most probably caused by the egr pipe from the exhaust leaking, adding too much air to the intake. It would seem that either the pipe is wholly cracked, or just a little, as the warmer the car gets (longer it runs) the misfire gets worse, affecting highway driving and cruising. Thus the crack must be expanding... Then, when the car cools down, its like everything resets. My concerns: If it were an EGR pipe leak, shouldnt I be hearing the sound of an exhaust leak? Popping, dieseling, etc? It doesnt seem to be doing that... or perhaps I am just used to it. There seems to be quite a bit of warm/hot air coming from the passenger side of the engine bay. Any thoughts? I would like to see if I can confirm this diagnosis before I buy the pipe and spend a day putting it in. Thanks!