My 98 SC300 with VVT-i has recently developed an idling issue when in gear.

It will occasionally (actually becoming very frequent) idle down to around 2-300 rpms and the car vibrates terribly.



I've searched but cannot find anything more specific to my issue.

The CEL is not on, no hesitation. Car runs great, just coming to a stop while in gear after warmed up it will idle so low it vibrates...BAD.

I have found and fixed a few cracked vacuum lines but it has not made a difference.

Any suggestions?

 

clean out the iacv. you'll most likely have to take off your tb to gain access to the bottom screw though.

 

I'll have to research that as I have no idea what or where it is. Similar to Idle Speed Control Valve like on my MKIII Supra?

 

Just read that VVT-i SC300 does not have an IACV. Now what?? haha

 

Yes your car has an Idel Air Control Valve. And yes it's probly bad. Disconect the IACV and if it doesn't change then start looking for one.

You can clean it and see if that helps if not start your quest.

Keep us posted.

 

Is it the big black thing right next to the TPS?

 

Is there any pictures of it? I've always wondered what it looks like.

 

I'm bumping this hoping someone will see and offer some help.

 

When was the last time you chanded the Plugs, cap/rotor button ??

Also I had this same issue with the 3rd Sc300 that I just perchased. the Cap/rotor, and plugs were Toast.

But the Major ISSUE I had was the MAF was bad and caused a Very Low Idel and would stall on startup and sometimes at traffic lights unless I held the gas a bit.

 

I had the problem where when the car's warmed up and I was stopped at light, the idle would suddenly and randomly drop to 400 rpm, stutter and slowly work it's way back up. It then got worse and the engine would die when I was coasting to a stop and pushed in the clutch. I took apart the whole intake/tb system, took off and cleaned the 2 sensors (ISC and IACV) on the front of the tb where the idle bypass tunnel is, cleaned out the inside of the tb/y-pipe/intake runners (probably totally unnecessary but it was pretty gross so I said 'why the hell not') and the car now idles perfectly now.
The only reason why I took off the tb was b/c i have no tools that could reach the bottom screws of the 2 sensors.

 

The plugs and wires were changed last year. I have coil packs so no cap/rotor.

Well see this is where I'm confused. My engine is a VVT-i and some people are telling me I do NOT have an IACV and some are. I know that where the IACV is on non VVT-i I have what is called a Throttle Control Motor. I don't want to be taking stuff apart until I know exactly what I got and what I can and cannot do to clean it.

Here is my engine bay:

 

Anybody?????????

 

Bumping for help if any.

 

There's a 10mm screw (that you can use a 10mm socket on it) located right in the middle of the Accelerate Lever Assembly to hold the Acc Lever Assem. You can use that to recalibrate your idling issue. Loosen the screw will cause the your idle to go up and tighten it will cause your idle to go down. Becareful with the screw as you don't want it to get too lose or else you're gonna have a hard time fixing it.

I would do this with the engine off first, in your case you only need to un-tighten the screw just a little, like give it a 10-20 degrees turn counter clockwise. I hope this help since I have a 98 Sc300 too, and I was having a similar issue just like you after I rebuilt my cylinder head.

Otherwise, It could be your fuel related issue or you need a new PCV valve. What's the milage on the car?

 

Thanks! My car has 201800 miles on it. The PCV has not been changed since I've had the car, which has been one year, and I've put almost 40k miles on it this past year. I will see about replacing that tomorrow.