Lexus IS250 (2008) rough idle when held in drive or reverse

[Alexhemming097]

Hello Lexus Owners Club! 

First time posting! my 08 IS250 has started playing up after some recent repairs.

I had my auxiliary belt tensioner replaced earlier in November and then a few days after I got the car back, the alternator failed and so that was replaced also (both at a local independent garage). All seemed fine once the car was back. Didn't replace the Battery as whilst the Battery was completely drained when the alternator failed, its about 2 years old and seems to be holding charge ok. 

On my first commute to work after getting the car back (20ish miles), I noticed at a set a set of lights the idle was rough. The rev counter was bobbing up and down between 500 and 900 rpm (ish). On the drive home, all was fine. I know when the Battery is completely dead for a period of time the engine management can 'forget' certain parameters and needs to re-learn them, so assumed it was that. I've also cleaned the throttle body and MAF sensor looks clean. (both as advised by other posts on here and elsewhere when others had similar issues)

A couple of weeks on and the car is still idling rough when held in drive or reverse (so happens when you stop at lights, or are parking, etc). Its intermittent and does not always happen. When it does happen, I notice that the clock appears to pulsate and if the interior light is switched on, this also pulsates (as do the brake lights). when the rough idle has started and the engine is under acceleration, the interior light also pulsates. 

Interestingly, if I put the car in drive and hold it on the brake and I'm getting the rough idle, it seems to stop if I turn the lights on or put the blower fan on full. As soon as I turn either off (whilst in drive/reverse and foot on brake), the rough idle starts again. 

 

I've managed to capture it happening if that helps: 

 I've got the car booked in at the start of Jan but any ideas would be greatly appreciated. I did think about a new Battery but if that's holding its charge then not so sure that's the issue? I would think alternator but that's just been replaced (when the idle is rough the alternator voltage drops but that seems to be in line with the RPM dropping). Otherwise, there don't seem to be any notable changes when actually driving.

Any help/ideas appreciated. 

Cheers. 

[steve2006]

Hi Alex and welcome to the LOC.

As this appears to coincide with the alternator being replaced I would be looking around that area, was it a recon or new OEM replacement?
With all the symptoms it would suggest the voltage regulator within the alternator is playing up, a loose connection or poor earth.

Easy way to check is to check the Battery voltage and see if it is varying with the RPM or get one of those cheap cigar lighter socket plug in voltage display units which would be easier to monitor while sat in the car.

[Alexhemming097]

40 minutes ago, steve2006 said:

Hi Alex and welcome to the LOC.

As this appears to coincide with the alternator being replaced I would be looking around that area, was it a recon or new OEM replacement?
With all the symptoms it would suggest the voltage regulator within the alternator is playing up, a loose connection or poor earth.

Easy way to check is to check the battery voltage and see if it is varying with the RPM or get one of those cheap cigar lighter socket plug in voltage display units which would be easier to monitor while sat in the car.

Thanks for the reply Steve! 

It was a brand new alternator, although I must admit I'm not sure whether it was an OEM or aftermarket part. Didn't think to ask at the time (in hindsight I quite probably should have!). As the problem only started after the alternator replacement, it does feel like the problem may well be in that area (whether alternator, regulator or connection/earth as you suggest).  It's quite intermittent and the curveball I noticed today was switching the lights on (or blower on full) seems to stop the rough idle/fluctuating voltage. Turning the engine off and back on also stops it for a bit. 

I bought a cheap Battery and alternator tester from Argos a little over a week ago (Buy Hilka Battery & Alternator Tester | Car battery maintenance | Argos) and this shows the alternator as working when at idle. But when I engaged drive and the rough idle started, the output did appear to be fluctuating with the change in RPM. It's a bit crude though as it only uses coloured led's. 

She is booked in for the 2nd Jan for a service and to have this looked at again. If the part was aftermarket and is playing up, I think perhaps going for a Denso part may be worthwhile (pretty sure the OEM part is Denso?), unless it does turn out to be a connection/earth. 

[steve2006]

No problem Alex,

Please keep us updated on the problem and hopefully the cause and solution 😀

[PMaisey]

Hi there, my first post as well. I have exactly the same issue with my wife's 2010 IS250 in Perth, Western Australia. First sign something was not right was the Battery warning light coming on briefly, then going off. Same with the alternator light. A check of the Battery showed it was not holding charge so that was replaced. During the replacement process, the alternator output was checked and it was about 12.5 volts regardless of the revs, so obviously the output was not sufficient to maintain the Battery. There were no error codes recorded. 

I subsequently ordered a replacement alternator from one of our aftermarket suppliers (Repco) and fitted that. It was a bit of a pain and was spread over a couple of days, so the power to the car was disconnected during this time. The pulsing started after this time. After trying a number of things, I accepted defeat and after speaking to the local Lexus service manager, I put it in, based on his recommendation, to have the engine decarboned. Not an inexpensive exercise at $880 Oz. The ECU was also baselined at this point and when I picked it up it seemed to have made a difference. 

Unfortunately, it was back again the next day. Spoke to Lexus again and arranged to drop it off for further investigation. They range back to say they thought it was the new alternator which was creating the issue. They tested it by running the car with it pulsing, then connected a second Battery to the car Battery (via jumper leads) and the problem went away. Disconnect the second Battery and problem returned. As we are thinking of selling the car, and the replacement genuine item is $2,700 Oz to supply and fit, I said I would give it some thought and let them know if I decided to go ahead. They said the output from the alternator was like a staggered output sort of like this with ups and downs.  ___l----l____l They said that the genuine item was more like a sine wave ~~~~~~. 

I haven't had a chance to replicate their testing with the second Battery but will look at that in the next day or so. To me the variable output seems to be a function of the regulator which is built into the alternator, but I am no expert. It would seem strange that would be faulty in a new alternator, but I'm sure these things happen. This is the unit I installed OEX Alternator 12V 150A Denso Style - DXA4049

If anyone has any suggestions or comments, I'm all ears. 

Cheers

Paul

 

[steve2006]

Hello Paul and welcome to the LOC.

Have you checked the Battery voltage since the work was carried out, firstly the “standing voltage” when the engine and ignition are both off, then with the engine running at idle and finally with the engine RPM between 1500-2000?

Car alternators produce 3 phase sinusoidal AC which is then rectified by 3 sets of half wave rectifiers ( 1 set per phase) to produce the DC supply required.

After rectification a small amount of the AC component known as ripple is still present but tends to be “smoothed” out by the Battery capacitance ( this is the ~~~~ Lexus mentioned to you) 

The DC output is then regulated by regulator to ensure the output voltage is within tolerances to prevent over or under voltage dependant on the electrical demand of the car and prevent damage to the Battery through over charging.

The regulator works by rapidly switching the DC output on and off via an electronic circuit.

Given that by connecting an additional Battery ( effectively increasing the load on the alternator) the voltage stabilises and the strange waveform looking like a square wave I would agree the alternator particularly the internal voltage regulator is faulty.

If you could post up those voltages it would help me further to help you.

 

[PMaisey]

Hi Steve,

Thanks for your reply. The following data is provided as suggested:

No Load

Off: 12.97 V

Idle: 14.27-14.28 V

1500-2000rpm: 14.30-14.31

 

Load - High beam headlights, aircon and fan on full, radio on

Off: N/A

Idle: 14.13-14.15 V

1500-2000rpm: 14.21-14.24 V

As an aside, I have tried to replicate the pulsing this morning and have been unsuccessful. Have done all the things I would normally do to make it happen, but not playing. The only things I have done are to removed all the engine covers, disconnect the cable retaining bolt and bracket which attaches to the engine for the main positive lead (it did free up the tension on the alternator connection), and removed the rubber sleeve which covers the positive alternator connection.

When I originally fitted the alternator, I did break off a bit of the plastic which sits under the positive connection on the alternator and I'm not sure if there may have been some arcing when under the rubber sleeve? Long shot, highly improbable, but who knows. Also maybe the plastic engine cover was pushing on one of the connections underneath it and creating an issue. Or maybe the retaining bolt and bracket were creating an issue. A bit of straw clutching going on here 🤪 but nothing else has changed. 

Anyway, I will leave it in its current state and we'll keep driving it and see if the problem returns. Then I can do some more tests.   

Hope the figures above are what you're looking for. Love to hear you thoughts.

Cheers

 

 

 

[Mr Vlad]

Have you used Techstream to see if there are any issues it may pick up? 

I remember vividly when the alternator on my beloved is250 packed up. Straight to Lexus for them to sort. Worth every penny. No issues whatsoever after I got the car back.

[PMaisey]

1 hour ago, Mr Vlad said:

Have you used Techstream to see if there are any issues it may pick up? 

I remember vividly when the alternator on my beloved is250 packed up. Straight to Lexus for them to sort. Worth every penny. No issues whatsoever after I got the car back.

Thanks for the heads up. No, was not aware of the Techstream product, but will investigate and see if it could be useful in the future. With my current issue, there were no error codes thrown up so not sure if Techstream can go beyond this level to id issues? 

As mentioned to Steve above, the car has been running faultlessly after some tinkering today, so we'll keep using it and see if the problem reoccurs. Fingers crossed. 

Cheers

 

[ColinBarber]

4 minutes ago, PMaisey said:

With my current issue, there were no error codes thrown up so not sure if Techstream can go beyond this level to id issues? 

That would depend if the tool you used to read codes is able to read all Toyota specific codes and not just generic OBD codes.

[PMaisey]

Here's an update:

Problem reappeared today and after a bit of research I found the following:

OEX RLO and S Alternator Regulator Function Tester

In a world where vehicles are getting more and more complicated, picking the right alternator can be difficult. A problem amongst many Toyota Camry and RAV4's that use the 2AZ-FE engine, there are two different types of alternator, based off the regulator function, but their plugs look virtually the same. One type of alternator has an S function, also referred to as "Sense" and one is "RLO" which is "Computer Communication". Long story short - it causes all sorts of headaches ordering the right part for the job.

OEX have taken the guess work out of it with a simple tester.

The ACX6250 simply plugs into the harness which would normally plug into your alternator. You turn the vehicle to ignition (vehicle without starting) and with the flick of a switch to identify the regulator function.

The alternator I installed was an "RLO" type and I am assuming I need the "Sense" type. Will confirm with the distributor tomorrow, but it would appear, given the symptoms, that will be the issue. My symptoms are now identical to Alex in the original post and by switching the lights on (and creating a load on the alternator) the problem goes away. But it seems if you have the lights on when you start the car, you can also get the issue. The voltage bounced between 13.05 and 13.95 when the issue is present, then flattens out to around 14.20 when it goes away. 

Keep you posted. 

 

[Mr Vlad]

Well I suppose that's what one gets when they don't go to a main dealer for an important electric component for a car, yes being old, but needs Proper maintenance and not from a third party establishment. 

[PMaisey]

9 hours ago, Mr Vlad said:

Well I suppose that's what one gets when they don't go to a main dealer for an important electric component for a car, yes being old, but needs Proper maintenance and not from a third party establishment. 

Yep, thanks Vlad, that's very helpful. 

[PMaisey]

Final Update:

OEX, who are the distributor for the alternator I installed, advised there was a later version of the alternator I had been supplied by Repco which addressed the issues I was having. They had replaced the regulator in this later alternator with an updated version based on the genuine Lexus regulator. 

They airfreighted me a replacement overnight, told me to bin the old one and I installed the new one the same day. Have been driving for 3 days now and has not missed a beat. So for me it was worth the inconvenience of having to put up with the pulsing for a short time and being able to resolve the issue for a total cost of AU$420 versus Lexus quote of AU$2700. 

I would suggest to Alex who started this thread, go back to the installer, find out what alternator was installed, and if it was an OEX, have him contact the distributor and get them to supply the later one. The only issue should be the time to replace which based on how long it took me to remove and install, should be a maximum of 2 hours or you might want to push for no charge. 

Anyway, all is well, that ends well. I'm a very happy camper. 

Cheers

Paul

[Alexhemming097]

Thanks for the replies all. I checked with the garage when the car was in for its service/MOT Paul, the alternator installed is manufactured by Hella. They plugged it in to diagnostics and couldn't see anything but I guess that's not surprising with there being no warning lights on. Also as is typical the fault did not replicate itself either when it was in the garage.

Before Christmas I bought a voltage meter that plugs into the 12v socket so have been keeping an eye on what its reading. Under normal conditions its sits at 14.2 (+/- .1 depending on what electronics are being used etc.). When it was doing the rough idle/pulsing, it would drop to 13 and the fluctuate similar to in Paul's case. But then if the lights were switched on (side or dipped), the voltage would stabilise back at 14.2.

Having said that, it seems to have settled now and hasn't been pulsing since I got it back on the 2nd. 

For now I'm going to keep an eye and see how it behaves but if the problem comes back I think it'll be a case of changing the alternator, going by what's been discussed. 

Cheers for all the info/advice. Most appreciated. 

[gulargambone]

On 1/10/2024 at 11:11 PM, PMaisey said:

Final Update:

OEX, who are the distributor for the alternator I installed, advised there was a later version of the alternator I had been supplied by Repco which addressed the issues I was having. They had replaced the regulator in this later alternator with an updated version based on the genuine Lexus regulator. 

They airfreighted me a replacement overnight, told me to bin the old one and I installed the new one the same day. Have been driving for 3 days now and has not missed a beat. So for me it was worth the inconvenience of having to put up with the pulsing for a short time and being able to resolve the issue for a total cost of AU$420 versus Lexus quote of AU$2700. 

Cheers

Paul

Hi Paul,

I much appreciate your input on this issue. I am exactly in the same situation. I bought the exact same alternator and have precisely the same problem. And, I have tested it as advised and it behaves exactly the same way.

So, thanks very much for your posts. I'll call OEX tomorrow, and hopefully they'll send me a new alternator as well, without any issues.

I agree, a $2,700 Lexus alternator when my Lexus is only worth 3-4k does not make any sense.

Cheers,
Peter