Well, I picked up the '89 4Runner yesterday, drove it home, and I noticed something weird.

While stopped (in 2WD only), the idle will raise then drop. But when the 4WD is engaged it idles just fine.

I talked to the guy I bought it from, and he said he had the same problem and he replaced some vacum lines trying to fix it.

I'm going to look at them again, because to me it sounds like a vacum leak. Is there a problem with the brake booster? Or maybe the vacum pump?

Thanks for the help!

 

I would check the tps and make sure its adjusted right, then check for vacuum leaks.

 

Likely the idle speed is too high. See the 2nd Q&A on the web page below:
- http://www.4crawler.com/4x4/TLCA_Tru...ech.04.09.html

 

Awesome! I'll give it a go tommrow. If not then I guess it's time to replace brake booster.

On a strange sidenote.

It only happens in 2WD. Once the engine has warmed up. Not when it's cold.

You can depress the brake and shift it into and out of 4WD and it will cut out and come back as soon as you shift it.

But my problem is exactly as the one described, so I'll keep my fingers crossed that's it.

Thanks guys!

 

Likely that ECU feature (cutting fuel while braking) is probably only done in 2WD mode since it is partly there to control emissions and also for on-road driving safety to help you slow to a stop faster. But in 4WD mode you might not want to have that sort of interference from the ECU. But if things are set up properly, you should never feel that fuel cutout. I never feel it on my '85 but I can boost the idle speed up above around 1000-1100 RPM and it'll instantly start doing that surging idle with the brakes on.