Sturds

Ok so I made a post a little while ago about my exhaust and seafoam in my '02 SC430, well the initial cause for noticing these things was a rough low Idle, last month I blew a radiator but shut the engine down almost immediately so no overheating or dry pump running, then had new radiator put in and mechanic changed timing belt and water pump and now it idles ok in park but in gear its rough enough to make you want to shut the car off, and almost causes some numbness, like sitting on a vibrating massager. I've cleaned the PCV line and replaced the PCV valve which helped just a little and seafoamed the daylights out of it and completely fogged out the road three times!! And still nothing but rough idle, on our RX300 there is a IACV valve that I've cleaned to solve this before but I don't know where it is on the SC430, any help on location and on the rough Idle? I also thought I read somewhere that if the timing is off a little between the cams it can cause this or will it ruin the engine first?

MDames2

iTrader: (1)

My wife's '03 SC430 also had quite a rough idle when in gear. We replaced a couple of the motor mounts, and this took care of the problem. Perhaps you have the same issue?

kjcole

Certainly inspect the motor mounts, but then consider the usual tune-up items (MAF cleaning, plugs, filters). I'm assuming no codes. There are some nice (and inexpensive) code reading programs (to use with your laptop) that allow you to dynamically monitor vehicle sensors in real-time as you shift from neutral to park, for example. Or while you drive. You can pick up stuff that won't cause your vehicle to throw a code.

The usual list: EGR, PVC, idle air control (IAC), throttle body dirty, MAF dirty, slight vacuum leak somewhere. Maybe motor mounts - inspect for leaks, and watch the motor while someone shifts from neutral to drive to see if it lurches sideways. Not sure if transmission mounts would be a candidate.

Kelly

jasone36

Definitely consider replacing the motor mounts. Mine shook like crazy before I replaced them in my 2002, and now it's much smoother in idle, but the shakiness is not entirely gone. Feel free to look through some of my previous posts on the motor mount subject.

ser67

Check your oil - a simple oil change stopped my rough running.

gripau1

Also check the plastic inlet manifold pipes for leaks or not tighten. When I first got my SC430, one of the large inlet clamps were not tighten. The car would feel like it would stall.

Scarletti

KJ, can you put some names (and URL's ideally) to the code reading programs you mention please?

kjcole

I have this one

http://store.mp3car.com/OBDLink_SX_2..._p/com-145.htm

There are cool ones for your Android phone (bluetooth)

sebtown

kjcole, does that one read any of the proprietary codes?, like any of he top motor codes?

diagtime

No IAC valve, just electronic throttle body. When you say idling rough, do you mean it shakes like hell but at normal idle speed or do you mean idle speed is really low? did it happen right after timing belt? timing belt off a tooth should throw a code. so should vacuum leaks and other running issues. how many miles have you driven it since this started? does turning a/c on or off change it?

kjcole

I don't know if it reads proprietary codes for Lexus. I think that you can purchase additional software (CD) from company for more extensive codes, but not sure about Lexus top codes. Pretty specialized for the SC430

Sturds

I have a reader had a misfire code cleared it still rough idle and at a lower rpm, started right after belt AC doesn't change anything idles up a little then slows again, all o2 sensors working fine. Sometimes its a little rough and other times it makes you want to get out of the car, after about 100 Miles of driving the misfire hadn't come back on and no other codes i assume the misfire is from the seafoam had trouble starting after using it but seafoam its cleared out and it starts normal but still low rough idle??? Makes no sense at all.

diagtime

how low is the idle? they idle pretty low to begin with. trying to figure out whether it's abnormally low and that makes it feel rough or if it's missing at idle.

in the meantime, try cleaning the throttle body. it should definitely bring the idle up short term, you'll have to put some miles on it to see if it helps long term

tips on cleaning throttle body.
KEY OFF.
don't spray throttle body cleaner in there. take the intake snorkel off, get something to hold the throttle plate open. spray throttle body cleaner on a rag and clean the grime.

it probably wont fix your problem but it's cheap and relatively easy. worth a shot.

if that doesn't work try compression test. you can bend a valve if you aren't careful replacing the timing belt. you can also mess up the crank sensor pickup ring but that usually causes problems all the time or only at higher rpms.