Inconsistent idle revs at different times

[perseuss69]

Hi

2008 IS250. Every time I put the car in park with the engine at operating temp and the AC off, the engine idles at a different RPM. I asked the dealership and I was told that the idle revs should be 700 +/- 50 RPM. Mine can be from about 750 to nearly 1000. I was unable to find any vacuum leaks. I'm also having issues with my automatic transmission, and the garage that specializes in them said that they think it's the engine instead. High idle was also the reasoning that they gave me.

Does anyone have any ideas? Or is this normal?

All of the attached images were taken at different times.

[Linas.P]

What revs we are talking about here and what conditions? 

700 +/-50RPM is the perfect idle speed for BRAN NEW warm engine in P. As you go trough gears the RPM will change, as well if you use any accessories, again RMP will fluctuate. 1000+ RPM is fine for cold start and warm-up, but it should drop down below 1000 after couple of minutes. I think if you just came in the morning and turn on the engine, then anything up-to 1250RPM will be normal and it will drop down.

Now obviously with mileage and wear, you won't get this perfect idling, I definably would not expect this perfect idle at 167k. So maybe you have a little dirt on throttle body, little bit of dirt in MAF, little bot of carbon on valves, in injectors etc. etc. it will depend on the fuel as well, on the temperature outside. So I would say anything between 650-1000 RPM would be normal. If the car is warm all accessories are off and it is still above 1000RPM, then it is not ideal. 

What issues you have with gearbox? 

[perseuss69]

1 minute ago, Linas.P said:

What revs we are talking about here and what conditions? 

700 +/-50RPM is the perfect idle speed for BRAN NEW warm engine in P. As you go trough gears the RPM will change, as well if you use any accessories, again RMP will fluctuate. 1000+ RPM is fine for cold start and warm-up, but it should drop down below 1000 after couple of minutes. I think if you just came in the morning and turn on the engine, then anything up-to 1250RPM will be normal and it will drop down.

Now obviously with mileage and wear, you won't get this perfect idling, I definably would not expect this perfect idle at 167k. So maybe you have a little dirt on throttle body, little bit of dirt in MAF, little bot of carbon on valves, in injectors etc. etc. it will depend on the fuel as well, on the temperature outside. So I would say anything between 650-1000 RPM would be normal. If the car is warm all accessories are off and it is still above 1000RPM, then it is not ideal. 

What issues you have with gearbox? 

Thanks for the response.

All the pictures are taken at similar conditions. I only compare idle revs when the engine is at similar conditions each time: at or near operating temp (85-90C), AC off. If I go for a drive and park the car, the engine might idle at about 800 rpm. Now if I go for another drive either on the same day or later, then after parking the car might idle at 950 rpm. It seems weird to me that it's so inconsistent. I cleaned the valves at 167100km, cleaned MAF yesterday and the throttle body was cleaned a few thousand km ago. Should be decent.

Regarding the transmission: it has jerky shifts especially when its cold. I was told that if the problem is worse when the transmission is cold then it might be oil related. Had an oil change and nothing changed. Went to another garage/shop and they said that they think it's the engine since the car/transmission doesn't have much mileage on it. They said that's what their experience tells them and that taking a look at the transmission would be a waste of money.

[Linas.P]

167k kilometres is about where I would expect you need transmission fluid changed. Although it is very picky on the level and the procedure is very specific, so many shops that are not specialist in transmissions does it in correctly and makes issue worse. Jerky shifts could be result of dirty ATF, or wrong level of ATF, or it could be issue with valve assembly (solenoids).

I agree that issue could be engine related, but 950RPM is nothing out of ordinary... it should be way higher/lower before it causes issues.

Are there any codes related to anything, even before you replaced transmission fluid? Have the shop taken out the sump and replaced the filter? 

[perseuss69]

1 minute ago, Linas.P said:

167k kilometres is about where I would expect you need transmission fluid changed. Although it is very picky on the level and the procedure is very specific, so many shops that are not specialist in transmissions does it in correctly and makes issue worse. Jerky shifts could be result of dirty ATF, or wrong level of ATF, or it could be issue with valve assembly (solenoids).

I agree that issue could be engine related, but 950RPM is nothing out of ordinary... it should be way higher/lower before it causes issues.

Are there any codes related to anything, even before you replaced transmission fluid? Have the shop taken out the sump and replaced the filter? 

The shop I took it to is extremely busy and well-regarded. I can't remember if they replaced the filter. I doubt they opened it up so probably just changed the trans oil. There haven't been any codes related to anything.

[Linas.P]

The other option could be Lamda/o2 sensors as they usually last ~160k (75-100k miles). So you are just at the time they need replacing. This could be checked by looking at live data and fuel trims. 

Just to be clear - these all suggestions are little bit speculative, so take them with pinch of salt. So far what you have described doesn't point to any particular problem related with the engine. 950RPM isn't abnormal to the point where it should cause any issues. For example maybe engine fan is running when you drive a car for a bit and stop? There is just so many possibilities of why it would be slightly higher than normal.

[perseuss69]

55 minutes ago, Linas.P said:

The other option could be Lamda/o2 sensors as they usually last ~160k (75-100k miles). So you are just at the time they need replacing. This could be checked by looking at live data and fuel trims. 

Just to be clear - these all suggestions are little bit speculative, so take them with pinch of salt. So far what you have described doesn't point to any particular problem related with the engine. 950RPM isn't abnormal to the point where it should cause any issues. For example maybe engine fan is running when you drive a car for a bit and stop? There is just so many possibilities of why it would be slightly higher than normal.

I had diagnostics done and nothing seemed out of the ordinary. Only thing that stood out was that the suction control valve position did not change when the engine was revved in park. Not sure if that's how it's supposed to work?

Another thing that maybe you could answer: when I put on cruise control at 100kph and the transmission shifts from 5th to 6th, the revs drop to 2k after the shift and then visibly drop to about 1900. What's that about?

[Linas.P]

Not sure about SCV operation, but if tit does not operate properly it would cause all sorts of issues with engine. But at the same time you would get engine light if it would simply be faulty.

As for RPM speed, sound about normal for gearbox to do that, depends on how long it takes from RPM to settle after gear change, what you doing with pedal, if the car is going up/down hill. Nothing immanently wrong with what you described. Sure if it takes like 10 seconds to settle after shift of perfectly level and smooth road then it could be a gearbox issue (sticking solenoid or something along those lines, low ATF could cause it as well), but again for just 100 RPM and maybe for a second or so, that is tiny problem. 

[Spock66]

26 minutes ago, perseuss69 said:

Another thing that maybe you could answer: when I put on cruise control at 100kph and the transmission shifts from 5th to 6th, the revs drop to 2k after the shift and then visibly drop to about 1900. What's that about?

Could be the torque convertor locking (which is perfectly normal).

[Linas.P]

21 minutes ago, Spock66 said:

Could be the torque convertor locking (which is perfectly normal).

That actually is precisely what it would be. IS250 torque converter lock-out 2-6th gear on A960E.

[perseuss69]

29 minutes ago, Linas.P said:

Not sure about SCV operation, but if tit does not operate properly it would cause all sorts of issues with engine. But at the same time you would get engine light if it would simply be faulty.

As for RPM speed, sound about normal for gearbox to do that, depends on how long it takes from RPM to settle after gear change, what you doing with pedal, if the car is going up/down hill. Nothing immanently wrong with what you described. Sure if it takes like 10 seconds to settle after shift of perfectly level and smooth road then it could be a gearbox issue (sticking solenoid or something along those lines, low ATF could cause it as well), but again for just 100 RPM and maybe for a second or so, that is tiny problem. 

Fair enough. The whole theory was that a sensor or something else might be a bit off but still in spec, so that there's no codes but still not working ideally.

[perseuss69]

25 minutes ago, Spock66 said:

Could be the torque convertor locking (which is perfectly normal).

 

2 minutes ago, Linas.P said:

That actually is precisely what it would be. IS250 torque converter lock-out 2-6th gear on A960E.

Interesting. Thanks for the info!

[Linas.P]

2 minutes ago, perseuss69 said:

Fair enough. The whole theory was that a sensor or something else might be a bit off but still in spec, so that there's no codes but still not working ideally.

That is what happens - I refer to that as "lazy sensor", usually applies to things like Lambda or o2 (but IS250 is literally sensor minefield, as are most of modern cars), so basically they are kind of late to react and not working optimally, but not so far out that it would cause the code to appear. This makes it extremely annoying to diagnose. 

[perseuss69]

2 minutes ago, Linas.P said:

That is what happens - I refer to that as "lazy sensor", usually applies to things like Lambda or o2 (but IS250 is literally sensor minefield, as are most of modern cars), so basically they are kind of late to react and not working optimally, but not so far out that it would cause the code to appear. This makes it extremely annoying to diagnose. 

I did something dubbed as a "throttle body relearn procedure" today. Will see if or how long it lasts. Thanks for your input. I appreciate it.

[Linas.P]

16 minutes ago, perseuss69 said:

I did something dubbed as a "throttle body relearn procedure" today. Will see if or how long it lasts. Thanks for your input. I appreciate it.

You can certainly disconnect the Battery for like 45min and let the ECUs to reset fully and see if it makes difference, but all in all nothing obviously is wrong with the symptoms you have described. 

That does not mean there is not issue, just that symptoms are very mild so far.