Irregular Idle Speed

[McLean]

The idle speed on my wife's IS200 Auto has been pretty irregular of late. So far I've found that once it's gone through the fast idle phase from cold (~1200rpm), the idle drops to just over 500rpm (in N or P) as shown on the tacho. At this point it sometimes stalls while coasting to a halt at a junction. Once it's properly warmed up - 15 minutes? - it idles mostly at about 700rpm as it should, but occasionally it drops to 500rpm.

I'm thinking sticky throttle control systems/sensors but before I open up the throttle barrel etc. and examine its bits, is there anything else I should check beforehand?

Thx.

[steve2006]

I would start with giving the throttle body a clean.

[McLean]

Just checking Steve - when you say give the throttle body a clean, do you mean the exterior or the interior? Just using carb cleaner?

Cheers.

[steve2006]

The interior, it is normally a build up of carbon on the throttle butterfly plate that prevents it closing properly so the idle speed is wrong.

The link below is for the LS400 proceedure as I cannot find one for the IS200 which should show the basics although there will be differences of course with connections,cables ,electrical plugs and fixing bolts.

Another thing to check are all the rubber vacuum hoses as a leak in these can cause idle problems also.

Don't remove the TPS (Throttle Position Sensor) a black thing with an electrical connector or it will need resettting, simply unplug the connector and leave it in place but try to avoid getting cleaning fluid in it.

http://www.lexls.com/tutorials/EFI/throttlebody.html

[McLean]

Hey, you're a star! It might be for a LS but at least I know what I'm looking for.

I'll be back...

[sjrainsford]

Having not looked as yet, do they not have an IACV?

[McLean]

Yes they do - part of the air intake chamber. I'll have a look at that and the vacuum system if the de-gunging exercise isn't successful.

[McLean]

Had the time to deal with this over the Xmas break - sorted!

A pre-spray with carb cleaner down the barrel (just removed the air filter) and outside round the accelerator cable/control spring area to soften up the gunge followed by a second go and hour later cleared it all off and restored regular idling speed. No need to open anything up this time round but thanks to Steve2006 for the detailed instructions - I'll keep them handy for next time ;-).