Hi guys,
Ive got a IS250 with nearly 30,000kms on it.

Recently, my engine idle speed has been unstable. It happens during stop and go conditions with A/C off. My idle speed sometimes drops down to 500rpm and i can feel the engine vibrating slightly as if its going to stall.
Whats the normal idle speed when the engine is warmed up? For the past year, my car's idle speed is around 650~750rpms. But Im not sure why recently its been so unstable.

Today when i stopped at the traffic lights, the rpm dropt down to 400rpm and I thought the car was going to stall, but the idle speed quickly kicked up to around 1000rpm and dropt down to 500rpm while the car was stationary.
When i turn on my A/C, the idle speed then stays around 700rpm, and I wont feel any vibration then.

Furthermore, recently ive noticed that the gear changes are slower. Especially when shifting from reverse gear to Drive, I need to wait for like 2 seconds till i can drive away or else i'll experience kick in the back feel(if you know what i mean lol). Ive never experienced this with my dads Audi A8 nor my brother's RAV4... is Lexus gearbox just slow?

Has anyone experienced this? Could it be carbon built up in my engine?

 

Not likely carbon build up. More likely a VVTi control valve is failing or a primary O2 sensor is failing. Both have been brought up here previously, but these are not common failures. I would take it to the dealer for complete diagnosis.

If yours is an '06, it may be affected by one or more TSIBs related to the engine as well. Definitely best to get it checked out and repaired under warranty.

 

----agreed----

 

How many different tanks of gas have you gone through during this unstable idle? If it's only been one or two, you might have just gotten some bad gas. If it's been more, then it might be something more serious.

 

maybe a bad batch of gas??? I'd still do what lobux said.

 

take it back and have them checked....

 

Same problem here.

I read in the past about the engine set to run too rich? Can someone confirm?

 

That's a different TSIB. You get an ECM reflash to address this issue. They originally had one TSIB, but recently separated it into MT and AT 250s.

And again, only a dealer can address this issue for you. It's warranty work, and they're aware there is a problem with some units.

 

thanks guys, sorry to reply this late.
Yes my car is 06 model. I'll get the dealer to diagnose it at my next major service which is about in a month's time.

Ive been using the same petrol ever since I got my car(Shell V-Power), however, there was one time i filled it with Mobile Premium and thats when i started seeing Check VSC.

However, I had seen the Check VSC error a few times and got them to diagnose it, and they told me they plugged it in and see no errors and just reset the ECU. Check VSC error happened a few times after the reset, however i havent seen it for almost 1month now.

I dont have faith in my dealer in diagnosing my car to be honest. Sigh... guess i'll get them to diagnose it again and hope they dont tell me the same crap.

 

I had similar problems while working on my piggy-back ECU since the OEM ECU wouldn't always see what it expected / needed from the MAF sensor. It would also cause the 'Check VSC' indicator to come on until I reset the OEM ECU. Have you done anything that might have damaged the MAF sensor (aftermarket oiled air filter, spray cleaners, etc.)?

 

My car is factory settings, no mods on it.
By the way, im not registered to grab hold of TSIBs, is there anyone that could provide me TSIBs for 06 IS250 models?

 

Have you ever washed your engine comparmtent with a high pressure sprayer?

 

nah, ive never washed my engine compartment.
Its clean as new.
Just tested it again and found out that the unstable idle is more obvious when the car had to come to a quick stop after I step on the gas hard.

 

Maybe you should check your ECU backup fuse. Previous cars that I've had would idle poorly (and even stall) during the 1st couple driving cycles after an ECU reset, so maybe your ECU is being reset every time you turn the car off.

 

That's not a possibility. There are two fuses that reset the ECM. If either does not work, the car does not start. I'm betting on the VVTi cam drive issue in the TSIB.