WeSki

Thanks for the tip but no I never got that far. One of the main issues was that the EGR tube that runs from the intake manifold to the right exhaust was cracked; the tube was pricy and a pain to change. There were multiple other issues with the car that were going to cost over $1000 in parts. The car had over 330K miles and wasn't worth $1k running. I found a 1994 LS400 with only 130k miles for $2500, bought that, scrapped out the 92, kept what I could use for the 94 and sold the rest on eBay. Made about $800. I drove the 94 for just over 180k, sold it and bought a 2000 LS400. Great cars.

I never did resolve the issue but I do think I found the last straw problem. The EGR tube the connects to the back of the intake manifold and drops down to the right exhaust had a crack in the accordion portion of the tube. At that point I punted, the cost of the tube and the labor time for me to change it out was just not worth it to me. I scrapped out anything that was of value on eBay, about $1000. Then hauled the scrapped out car to the scrap metal yard, $100. It was sad but it was the most I could get for a car that wouldn't pass CA smog and was going to cost a bunch of time and money to get it smog worthy. Best of luck to you all. I'm now at 211K miles on my 2000 LS400.

I'm looking for Test procedure for an EGR valve off my 1994 LS400. This is not the vacuum type but has the electronic stepper motor. Lexus Part No 25620-50020. This EGR has the same connector as the IAC. I have the test procedure for the IAC to move the valve open and closed (Applying VDC to pins 1-4 in sequence to close and 4-1 to open) and the EGR appears to have the same design (But bigger coil) and connector so I tried the IAC procedure on the EGR, no valve movement. I have 2 of these EGRs and the IAC procedure doesn't work with either. 2 bad EGRs, maybe but I doubt it. So I'm thinking that the test procedure is slightly different for the EGR. If anyone knows where to get a copy of the the EGR test procedure to test the operation of the valve I would love to get a copy. Any other feedback is welcome. Thanks.

I believe you are right, the controller would have to run the valve to full close or open and measure gases, fuel mixture or something because there is nothing on the IAC to tell the controller that the valve is in one position or the other. Once the controller determines the open or closed position I assume that controller keeps track of how many time it has sent signals to the IAC. I read a posting on the web were a guy reinstalled his IAC in the closed position and the engine would not start but took the car several starting attempts until it finally started. The poster speculated that the controller needed the attempts to recalibrate; I suspect he is right as from my research most engines won't start if the IAC is in the closed position.

After doing some internet research on stepper motors I made another attempt at testing my IACs. The procedure in my first post is correct. I tried a 9 VDC battery and also the 12 VDC car battery both worked fine. When applying DC to the IAC it is very difficult to see the valve move at least not by what my 20/20 vision can see. The momentary negative voltage must be applied in sequence and independently of each 'S' terminal i.e. apply negative DC to S1 then release, then apply negative DC to S2 then release, then apply negative DC to S3 then release, then apply negative DC to S4 then release. One round of applying and releasing negative DC to S1-S2-S3-S4 won't give you much movement in the valve in fact the first few times I attempted the the test I mistakenly ruled that either the IAC motor was bad but more likely that I was doing in wrong. My issue was that I wasn't repeating the apply and release cycle enough times to see significant movement of the valve. After repeating the negative DC apply and release cycle several times (S1-S2-S3-S4-S1-S2-S3-S4-S1-S2-S3-S4-S1...) I began to see significant close valve movement. Reverse the cycle (S4-S3-S2-S1-S4-S3-S2-S1-S4...) and after severe cycles you will see significant open valve movement. Other learnings; the stepper motor on the IAC is a 125 position motor according to Alldata. The valve head does not spin or turn only moves open of closed. The shaft of the stepper motor is threaded (worm gear) that is threaded on to the valve head. As the shaft on the stepper motor shaft turns in the valve head the valve head move in and out on the stepper motor shaft opening or closing the IAC valve opening. This has been a real learning experience for me and hopefully not a waste of time and cyber but will be of value to someone someday.

Thanks Exhaustgases, I haven't worked much with stepper motors but I am familiar with how they operate. I agree that a controller of sorts would be needed to move the valve open of closed but I have two test write-ups (Alldata & a Lexus manual) that both describe testing the IAC in the manner I described in my first post. In both test write-ups they show diagrams with the IAC connected to a battery; battery (+) positive to terminals B1 & B2, and the (-) negative to terminals S1-S2-S3-S4. There is one variation between Alldata and the Lexus manual; for connecting the negative to terminals S1-S2-S3-S4 Alldata uses the term of connecting the "negative to terminals S1-S2-S3-S4 in that order" while the Lexus manual reads "while repeatedly grounding S1-S2-S3-S4-S1". The diagram shows the positive and negative connected to the IAC all at the same time but that doesn't seem consistent with a stepper motor operation. I've tried every variation of connection the S1-S2-S3-S4 terminals to negative/grounding and nothing yet both test write-up lead me to believe that if done correctly the valve will move open or closed. Both test diagrams show using battery as the source to power the IAC but neither say what voltage the battery is, I can only assume that the battery is the 12 volt car battery but maybe 12 VDC is to much.

Hello All, I'm looking for a tried and true test write up for bench testing the Idle Air Control IAC valve (AKA Idle Speed Control ISC) off a 1994 LS400 (165K miles) Part # 22270-50020. The 50020 IAC has the fixed coil mounted to it unlike the earlier LS400 that has the 3 screws holding the coil on the IAC; part # 22270-50010. I have attempted the bench test from Alldata but I'm not getting the desired results. My IAC measures 44 ohms for each of the 4 windings which according to Alldata is too high. The IAC doesn't function when I apply DC to the valve motor to move the valve open or closed. I could have a bad IAC but with reasonable and four even resistance readings I'm thinking I may be doing the valve test wrong. Resistance test from Alldata: terminals B1-S1; B1-S3; B2-S2; B2-S4 all should be between 10 to 30 ohms. I've seen a posting that appears to be a lexus manual giving a range of 34-54 ohms. All four of my windings are right at 44 ohms. Valve operation test from Alldata: Connect battery (+) positive to terminals B1 & B2, and the (-) negative to terminals S1-S2-S3-S4 in that order. The valve moves in the closing direction. Connect battery (+) positive to terminals B1 & B2, and the (-) negative to terminals S4-S3-S2-S1 in that order. The valve moves in the opening direction. I have one of each (50010 & 50020) IACs. When I do the valve operation test I can hear, feel, and see the valve bump (more of a wiggle) but that's it. I tried pulsing the the Negative in the sequence described but nothing. The 50010 gives me a little harder bump than the 50020 but neither move open or close. I'm assuming/guessing that I should be able to see the valve move open or closed when I apply DC to the valve motor in the correct sequence. If anyone has performed this test successfully I would really like to hear from you and know if the valve should move with DC applied. Thanks.

Thank you both for your input and suggestions. Today was a good day, after weeks of no starts and erratic idle the car finally gave a check engine light and the TrackOff light. Here are the Engine codes: 24 Intake air temp. sensor signal 31 Air flow meter signal 71 EGR system malfunction Trac codes: 48 Sub-throttle position sensor signal is 4.3V or higher, or sub-throttle position sensor signal is 0.2V or lower when idle switch is OFF 51 Problem in engine control system The 24 & 31 sound like something to do with the MAF but I don't know I cleaned the EGR valve but didn't test it. The EGR on my 94 LS is electronic controlled, my 92 LS was vacuum controlled. Are there any good instructions on testing the EGR valve and EGR system? The TPS is easy to get to, again Are there any good instructions on testing the TPS? Wow, 51, sounds like Lexus engineers didn't know what to do with the random issues and rolled them in to one code. Can you say Punt. I would love to get some direction on this too. Thanks, your feedback is appreciated.

In the mornings or after the car has sat for a couple for hours it starts right up and runs fine. At least once a day turning off the engine after driving a few miles it won't start back up if I try to re-start it within 20-30minutes. This is random and I haven't been abel to determine any pattern or cause. After cranking the engine for about 10 seconds the engine maybe fires a couple cyclers then dies. Crank it for another 10 seconds and it will pop over again but won't start. This has been happening so much that I've gotten pretty go at getting the car started after 5 or 6 long crankings. Once I get it started it sputters and shakes then smooths out but at high idle, 1500-2000 RPM. Sometimes the idle will oscillate between 1200 and 1800 RPM after a difficult starting described above. The battery is strong and cranks the engine over easy and fast. Also after a couple 10 second crankings you can smell a lot of fuel fumes and no, I'm not pressing the throttle while trying to start the car. The car runs noticeable better in the morning when it's cold but after running for 15 minutes or so the idle RPM sometimes goes nuts; at a stop the idle may stay at 2000 RPM or oscillate up and down or idle real low to the point of almost stalling. When driving the car it runs with no issues, the trouble only occurs after coming to a stop or sitting down and then re-starting. I checked for engine codes; None ​Today I did the following: Replaced the Wire Set, Spark Plugs, Rotor, Cap (the best i could tell these have never been changed) Changed the Oil, Oil Filter, Air Filter Cleaned the Throttle Body, IAC, EGR valve ​After completing the above maintenance and cleaning the engine fired right up and ran smooth idling at about 1100 RPM; RPM dropped as the engine warmed up. when the engine reached a good operating temp the idle dropped to about 800 RPM in neutral, about 650 in Drive. The just a few minutes after the engine warmed up it began to oscillate 1200-1800 RPM. I let it oscillate for minutes then shut it down. I should of got out and watched the engine but didn't. I tried re-starting and to go through my routine described above; I got it started after 5 long crankings. Still no engine codes All comments welcome. Prostar 1994 LS400; 145k miles.

I'm having the same trouble or very close to it; did you ever find a solution? I'm driving a 1994 LS400 with 145k miles. Here's my story About 2 weeks ago after about 20 minutes of hwy driving, at a stop the car stalled, turned the key and it started right up. Over the last 2 weeks the car has stalled at least once a day and each time it takes longer to start back up. The battery is strong and cranks the engine over with no trouble. After cranking the engine for about 10 seconds the engine maybe fires a couple cyclers then dies. Crank it for another 10 seconds and it will pop over again but won't start. A week ago 3 or 4 ten second cranking it would start up but now after 5 or 6 ten second cranking it won't start at all. I have to let the car cool down for 3 plus hours and then it will start and run like nothing happened. Also after a couple 10 second crankings you can smell a lot of fuel fumes and no, I'm not pressing the throttle while trying to start the car. The car runs noticeable better in the morning when it's cold and begins to run a bit on the ruff side after engine has reached temp and has run for about 20 minutes. All comments welcome. Prostar

Thanks for replying again, No, I won't run out and get new parts, just looking and troubleshooting. Thanks for the valve clearance info, I'm with you now, I just didn't make the connection from you last post. I pulled the IAC and cleaned it up, it wasn't to dirty however I found the following The resistance between pins is 22 ohms, the specs I found on this site call for 35 to 50 ohms or there about. I applied DC to the pins per the same post an nothing more than a bump in the plunger when applying DC. I also noticed a hair line crack in the black casing. I'm not sure where to go from here, new IAC? a used one on eBay? I searched for rebuild parts but no luck. I'm reluctant to spend too much on the car as it won't pass smog and CA will give me $1000 for it being a gross polluter. I feel like I'm almost there in getting the trouble figured out; I hate see it go but I don't know. Thanks again to all.

Thank You for your reply. I purchased the connector from Lexus, part 90980-11246. It is a common connector body for repairing connector to ignition coils for many Lexus and Toyotas. I only replaced the body of the connector the wires and pins were in good condition. No, the ECT has not been replaced, I will look into that. I've seen post on the ECU Caps, I'll look into that also. I haven't looked at the Idle Air Control Valve, I'll check that too. Yes!, I DID find a vaccum leak. One of the 3 vaccum lines on top of the Throttle Body was not seated. I must not have connected it when I clean the Throttle Body. After connection the line the engine smooth out but not completely. The Idle drop also but not all the way. The engine is now pretty much running the way is was before I cleaned the Throttle Body. I didn't see any other manafold leaks. I cleared the Codes and drove the car today and got a check engine light, Code 71. Cool we're making progress no more Code 24. EGR. A few weeks ago I did pulled the EGR and it was dirty and nearly pluged. After cleaning it I sucked on the vaccum line tube and it was real tight. At the same time I had someone watch the little rod inside the EGR move as I sucked on the line. I blew on the emissions tube and it seemed tight also but didn't actuate the vaccume diafram at the same time. Could I still have a bad EGR? The sysmptoms now are that the engine is still has a bit of a miss to it. It also is stays at a fast idle for long periods of time. I can run the engine up to operating temp and it will stay at a fast idle. Then after several miles of driving I will notice that the idle has dropped back down to the 650 RPM range and then the idle seems to be ok from there but the (what I am calling a miss fire) is more noticable. I don't understand what is meant by "mechanical type followers meaning that the intake and exhaust clearances need to be checked", can you elaborate? I will look into the O2 Sensors; they were replaced at around 245k miles. I really appreciate your input. thanks

1992 LS400, 328K miles The following was replaces at 300K miles: Timing Belt, Idler pulleys, Water Pump, Crank Seal, Cam Seals, rotors, Caps, Wire set, Spark Plugs At about 327,700 miles the Left side ignition coil failed; replaced both the left and right coils and that seemed to fix it. After driving the car for a short time I noticed a slight shutter at idle, kind of like a miss fire. I was getting 19 PMG but the shutter, kind of like a miss fire, got worse then the check Engine light came on. I also notice a reduction I power. Code 24: Intake air temp. sensor signal Code 71: EGR system malfunction The 12VDC plastic connectors to the Coils fell apart and replaced them with Lexus connectors; the wire and pins were ok. I have checked the following: All ignition wires; all within specified ohmic values Checked all spark plugs Left and Right Cam Positions Sensors: Both within specified ohmic values Cleared the code drove the car for about 15 miles (still a shutter at idle) when the Check Engine Light came on. Same codes. The car still runs pretty good at cruseing speed but I’m getting about 19 MPG HWY instead of 25 MPG Hwy. A website discussed that a dirty throttle body could cause a Code 71. I pulled the throttle body and it was filthy dirty. I cleaned it up and blew out the passages. The engine started right up but it now runs rougher and idles higher, 1150 RPMs, it used to idle at 650. I have driven the car for about 20 miles in this condition, no check engine light yet. I’m stumped. I welcome your feedback, hits, tips and tricks.

I have a complete set of tires & rims from the LS400 1992. If you are in So Cal (Vista area) then let me know if you would like to buy them. What rims do you have, the polished (Chrome looking) or the gray?

Here's my 2 cents. I messed around with aftermarket wires and it was a hassle. I bought the wires at Napa where I get a discount through my work and the wire set still cost $95. I got so frustrated with the aftermarket set that I went to the dealer. The wire set is pre-dressed with new guides and it took about 6 minutes to install them. I expressed my frustration with the aftermarket set to the Lexus parts guy and he gave me a break on the price at $113. Well worth the extra $18. Yes, I returned the aftermarket set. Good luck and have fun.