Moar Help Needed! Replaced Coolant Temp Sensor And Now More Proble

[CptYossarian]

Following on from my earlier thread here, I bought a coolant temperature sensor for £6.50 from ECP and have used the helpful tutorial linked to in that thread to do the work today with my dad. Both of us are absolutely amateurs and do not register on the DIY mechanic scale-of-aptitude, although my dad is an excellent DIYer in general and can identify bolt-sizes and different clips from 100 paces etc.

We spent 12 - 6.30pm on this job, and essentially, during this time we do remove the old sensor and then put the new one back in, and then putting everything back is kind of the reverse of the removal process.

It wasn't smooth sailing though.

We have to erect a gazebo hastily at around 1.30pm because of really heavy rain which arrived hours earlier than it should have done. Some of the parts we've taken off get a bit damp, one of these parts is a plastic air-intake manifold that probably shouldn't ever get wet because air goes through it and into the engine, which might explain why the car now has further problems.

We also accidentally snapped off a brittle hollow plastic tube guides the line on the left in this image onto the slightly thicker line above it. When reassembling we had to use glue to stick this back on, and then hope that it didn't fall off again when reconnecting the line. It didn't, and we used a zip-tie to try and tighten it but it isn't doing much. The discussion about that particular line is here but I don't really understand much, only that it's probably important and might explain why the car has the problems it now does.

After putting everything back together, I reset the ECU again so the car could "learn" the new sensor (not sure if this was wise or not), and turned it on. It still idles when cold at 1,900rpm, and then settles down to 600rpm after five minutes.

I then test drove it, and discovered that the EML now comes on randomly, and when it does the car usually suffers a severe and brief loss of power. The revs dropped to 200rpm at a set of traffic lights and it flashed on for a few seconds, then it went away until I put it under load and it came on again. The car juddered as if it's losing power or not firing, but only momentarily. Then it was fine one moment and pulled tremendously in 3rd and then a few minutes later it juddered again.

The EML doesn't stay on, it comes on and off randomly with no pattern or connection with how I'm driving. It doesn't sound like a misfire but I'm not sure what one sounds like.

Drove it back home. Thought...."we've been morons and the air intake manifold got a few teaspoons of liquid in it whilst sitting on the ground without anything covering it except a gazebo (it was exposed to moisture in the air and spray from rain hitting the ground. Decided to leave the car running for 15 minutes to see if it burnt the remaining moisture out the other end.

Go into house. Come back out 15 minutes later. Car has died at some point. Try to start car, barely cranks into life, and it's running awfully rich (as in, monoxide poisoning within 2 minutes if you stand within 2 metres of the back of the car).

Drive it again, same problem. Put it in cruise control at 30mph for 1.2 miles and it's fine.

The only silver lining here at least I've not paid £100 to have a £6 sensor fitted but I might have to pay a lot of money to have a more serious problem sorted, especially if, despite our careful attitude, we've managed to mess up a spark plug lead or something and now it's not firing in sequence.This is highly unlikely, but it doesn't feel like a cheap fix.

Also, further research would indicate that the high cold idle could also be caused by a shorted out mass air filter sensor, which is an easily accessible big black box on top of the car, costs £27.99 to buy from eBay and is infinitely easier to fit than the coolant temperature sensor.

Any help or assistance would be appreciated.

[ambermarine]

The pipe junction you have broken is critical to the running of the engine as it is part of the fuel management system and includes both the vacuum (small one) and the bigger one is part of the re-circulation of the exhaust gases feeding into the engine air intake,

They are critical because without them the wrong information is being picked up in the fuel/air mixture sensor (Maf) and that is why your engine light is going on and off and slow running is bad.

Replace the whole induction unit casing from a breaker and fix the vacuum pipe connection airtight or you will never get the engine to run properly.

[CptYossarian]

Eek.

Yes I can see that the casing is all inclusive and it is a very easy part to replace. I'll see how much it is on ECP, if at all, unless a breaker's yard is the only likely place to "stock" it.

[CptYossarian]

The pipe junction you have broken is critical to the running of the engine as it is part of the fuel management system and includes both the vacuum (small one) and the bigger one is part of the re-circulation of the exhaust gases feeding into the engine air intake,

They are critical because without them the wrong information is being picked up in the fuel/air mixture sensor (Maf) and that is why your engine light is going on and off and slow running is bad.

Replace the whole induction unit casing from a breaker and fix the vacuum pipe connection airtight or you will never get the engine to run properly.

Now fixed :).

So we do the paperclip method of shorting the correct pins in socket under the driver's knee as outlined here.

Nothing. No codes! Hmm. Weird.

Sowe go for a 15 minute drive, on a circular route that covers all sorts of roads. The car starts up and idles at 1,250rpm, but this is normal after an ECU reset.

It behaves like a Lexus on the drive. Smooth, effortless, sounds great. Tickover was a bit on the lowside...500rpm, and it dipped below 500rpm twice while stationary. Hmmm, not quite right.

Get home, it's now warm. Turn car off. Turn car back on immediately (phwoar - RICH!) and BINGO! There's the EML light. So we do the paperclip test again, and BINGO AGAIN! We have four error

codes:

Code 21 - Main O2S & Heater Signal

Code 22 - ECT Sensor Signal (this is the part we replaced in the first instance...whut?)

Code 27 - Sub O2S Signal

Code 28 - Main O2S

Okay, so all of these could have a significant impact on how the car runs. Some Internetting reveals that the O2 sensor signals can be thrown out by a leaky exhaust, although there's no noticable blow. What this would do, though, is make the car think "Hmmm, a bit lean...MOAR FUEL", which might explain the fact the car was running super-duper rich when cold, or at high RPMs.

This would logically explain why resetting the ECU by pulling the fuse "fixes" the high idling for a couple of days, until the ECU detects issues with the O2 sensors and says "wait a minute, something's wrong!" and then changes the idle speed.

It's strange that up to this point I'd not seen the EML light at all, though. I do suspect that the SUPER CHIP that the previous person installed might have something to do with all of this now - at first I

thought that the chip wasn't connected to anything or doing anything, but now I'm beginning to feel that it's utterly screwed up the car's brain .

Even more strange, the EML light went out on the drive home, and it began ticking over at 650rpm. It smelled very rich still, however.

Any ideas?

[Rupert Dubreaux]

Tom hi , I assume the now fixed part of your post means you followed Ambermarines suggestion and replaced the air intake between the MAF and the throttle body .

As you are not sure what state your main ECU is in, it might be a good idea to do the ECU ripple test (link below ) to check the ECU capacitors . If these are faulty or leaking all sorts of problems can occur .

http://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/715345-how-to-check-your-ecu-without-removing-it-from-car-by-yamae.html

The other slight worry from your post is the code for the ECT showing up ,this part is fairly critical to the running of the car . I am guessing by the amount you paid for the replacement you fitted, it wasn't a genuine part or even a branded OEM equivalent ,some of the cheap Chinese ones do not always perform well (being diplomatic there) .

Did you test your original with Steves temp and resistance check to see if it was faulty .

I hope you get it sorted soon so you can enjoy driving it .

[ambermarine]

The fault codes for O2 sensors are critical to the fuel mix as they will as you have discovered by your research alter through the engine ecu the fuel mixture.

The troubleshooting on any engine as to be logical or otherwise you just end up with no end or beginning .The original problem was slow running and the suggestion that the ECT sensor could be the cause ,is a possible cause ,now you have a O2 sensor that may be the cause and to all intents and purposes that is the one you need to resolve before any other.

They do fail and if so would be the cause of wrong fuel mixture being directed by the ECU.

There are tutorials scattered on the internet regarding O2sensors and also I think there is a tutorial on how to test them as working properly on the US Lexusclub owners site as well as removing and replacing these sensors.

I know how frustrated you will feel at the moment and an end to the problems may look difficult but the car was designed with a troubleshooting system built in and if you follow its Logic you will succeed.

[ColinBarber]

If you are suddenly getting error codes after doing some work then I'd suggest something like an O2 sensor isn't at fault. Seems an electrical issue in common with many of the engine sensors such as a poor earth, grounding strap or failing Battery.

[CptYossarian]

Thank you for your responses.

Tom hi , I assume the now fixed part of your post means you followed Ambermarines suggestion and replaced the air intake between the MAF and the throttle body .

As you are not sure what state your main ECU is in, it might be a good idea to do the ECU ripple test (link below ) to check the ECU capacitors . If these are faulty or leaking all sorts of problems can occur .

http://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/715345-how-to-check-your-ecu-without-removing-it-from-car-by-yamae.html

The other slight worry from your post is the code for the ECT showing up ,this part is fairly critical to the running of the car . I am guessing by the amount you paid for the replacement you fitted, it wasn't a genuine part or even a branded OEM equivalent ,some of the cheap Chinese ones do not always perform well (being diplomatic there) .

Did you test your original with Steves temp and resistance check to see if it was faulty .

I hope you get it sorted soon so you can enjoy driving it .

Hi, yes, we have replaced the entire part, and there are now no air leaks. The car drives absolutely perfectly (no juddering or sudden/brief losses of power).

Regarding the coolant temperature sensor, I bought this:
http://www.eurocarparts.com/ecp/c/Lexus_LS+400_4.0_1995/p/car-parts/engine-parts/fuel-and-engine-management/engine-management-sensor/?224660231&1&249771e521a68568d003667d41cabcb0c8a454a6&000572

This was what came up when I put in my car's registration (it might even show when you click the link), so I bought it. Unfortunately I may have committed a mistake - the logic we used was simply that it was cheap enough to buy and seemed easy enough to replace to not bother checking to see if the other one was faulty or not. Essentially, even if it wasn't, the new one wouldn't do any harm!

Maybe I'm now living to regret that slap-dashery.

The ECU ripple test looks interesting although unfortunately most of that entire post goes way over my head. I'll have to run it past my dad who is much more techy minded as he might understand what we're actually looking for by conducting that test.

The fault codes for O2 sensors are critical to the fuel mix as they will as you have discovered by your research alter through the engine ecu the fuel mixture.

The troubleshooting on any engine as to be logical or otherwise you just end up with no end or beginning .The original problem was slow running and the suggestion that the ECT sensor could be the cause ,is a possible cause ,now you have a O2 sensor that may be the cause and to all intents and purposes that is the one you need to resolve before any other.

They do fail and if so would be the cause of wrong fuel mixture being directed by the ECU.

There are tutorials scattered on the internet regarding O2sensors and also I think there is a tutorial on how to test them as working properly on the US Lexusclub owners site as well as removing and replacing these sensors.

I know how frustrated you will feel at the moment and an end to the problems may look difficult but the car was designed with a troubleshooting system built in and if you follow its Logic you will succeed.

The very original problem was a high cold idle of around 1900rpm...first it was suspected to be clogged throttle body, but as an ECU reset (via the fuse) changed the idle to 1,250rpm for a couple of days I was advised that it was more likely to be the coolant temperature sensor that was faulty (hence the delay in the car going back to its old ways as the ECU realises that a sensor was throwing a strange reading).

The air leak problem was simply caused by a bit of heavy handedness with old brittle plastic and has been rectified. The EML has only come on since we replaced the coolant temperature sensor - possibly because we ran the car with an air leak which might have caused all manner of strange readings to be sent the ECU's way which might in turn have made it instruct the car to do all sorts of daft things. It's hard to say - as you hint at diplomatically, our approach as non-mechanics has been a bit illogical and might have ended up placing us in a position where it's hard to now work out which direction to go in.

For clarification, I did a 10 mile drive from cold and it was absolutely fine. I stopped the car, turned it off, then turned it on again, and only THEN did the EML appear. To compound this, what perplexed me even more was the EML appearing when I started the car later in the evening to drive home, but then going off enroute!!

As you've all mentioned, this type of problem can indeed cause havoc! But nevermind, it's a £900 car, bought after a Saab began making "ouch my DMF" noises, so I'm calling this one a learning-curve.

My dad and I have briefly skimmed over the tutorials on the Internet relating to testing/replacing O2 sensors and it goes a little beyond what we are happy to attempt on the driveway.

I think it might be time for us to hold our hands up, write a "report" and then pass it over to a tame Toyota/Lexus independant!

At least the car can be driven again - sure I might get 10mpg but it's worth it to hear the quad-stainless-steel exhausts warble. :)

[CptYossarian]

Forgot to add, is there a difference between resetting the ECU by pulling a fuse and resetting it by disconnecting the Battery?

[ambermarine]

Thank you for your summary so far and as you say it is a learning curve, the issues do not require major surgery with the right equipment and knowledge.

A Lexus trained independant should be able to clear it up in no time,the episode for yourselves as done you no harm as you discovered what a masterpiece of engineering the Lexus ls400 engine is.

The removal of power by whatever means from the system as the same effect,to answer your ps.

[CptYossarian]

Yes, that's very true - it's amazingly simple to work on for a big V8 and the over-engineering of some parts is wonderful (and they remain simple to remove/work on!).

Okay, so removing the fuse has the desired effect. Somebody on another forum has suggested pulling the fuse overnight, reinserting it the next day, doing the paperclip test and reading the codes, seeing what it says, and taking it for a drive and then reading the codes again afterwards.

This will test whether the codes are actually being cleared by the ECU reset or not. It'll also perhaps reset the car to 0 as it's been messed about a bit by us, with new parts being put on, accidental air-leaks messing things up further...it must not know whether its coming or going :D.

This might be the final thing we do so that we can approach the Toyota/Lexus indy with a clear explanation of what's happened and what we need to happen going forwards.

[CptYossarian]

No EML at all today, car is still a little rich and tickover's a tad low, but otherwise running like a dream.

Maybe it's time to cover my ears, go "LALALA" and pretend everything is fine. :)

[ColinBarber]

Forgot to add, is there a difference between resetting the ECU by pulling a fuse and resetting it by disconnecting the battery?

No