High Idle on Startup - ideas?

[Jcreme]

I have a 93 FZJ80. It's round about 275k miles. Oil consumption is about 1 qt per 750 miles.

When I start it up (with the AC on), it idles at about 1800-2000 RPM for about 60 seconds, then drops to 1000-ish. Once I drive it a bit, it idles normally at 600-650.

Related issues:

• With the AC off, the behavior is similar, but idles at 1400-1500 on startup
• When I push the brake pedal, the idle increases slightly
• If I start it up with a hot engine, it is the same, but reduces to the 1000 rpm state after about 15 seconds.
• Sometimes after driving for a while the idle is low - 400ish
• Most vacuum lines have been replaced

I'm thinking vacuum leak? What do you think?

Thanks!

Justin

 

[inkpot]

Not unusual for OBD I rigs to have less than ideal idle manners. As long as it comes back down fairly soon, I would not worry about it.

 

[Broski]

I have a 94 about the same miles, It’s always done the high idle thing at cold start up, then comes right down.
It has never worried me.

 

[mudgudgeon]

Have a read here

http://www.lcool.org/technical/80_series/fast_idle/fast_idle.html

Simple mod to the IAC. I'll be doing this to mine at some point. The high idle on start up, and when AC kicks in drives me mental.
High AC idle up is almost dangerous, I find when I have AC on, the high idle is enough to keep the car accelerating when I want it to coast

 

[Jgrauman]

If you unplug the IAC does it do the same thing?