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'89 4WD V6 Idle Problem

I have an odd problem..

My truck has about 266,000 miles on it, and runs almost perfectly, except recently it started "stuttering" when my foot is on the brake. More often than not, when I have the brake applied, the engine idle drops suddenly to about 300 to 400 rpm then jumps back up to normal, down, then up, down then up, over and over about every 2 seconds or so, until I lift my foot off the brake, then it idles just fine. It does it as I slow for a stop, and when I am just sitting at a light, clutch in or out, in gear or not. However, it doesn't do it when the truck is cold, and the "high idle" is on, then once it warms up, and the idle drops to normal, it's back to the stutter when the brake is applied..

I thought it might be electrical, so I tried every combo of lights on, lights off, AC on, AC off, etc etc. but with no change in idle, then I press the brake, and "stutter, stutter, stutter".

Everyone I talk to is stumped, anyone have any ideas?

Thanks! James

Reply to
Roadie
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Your hot idle speed is too high.

For an explanation, here's an excerpt from a recent TLCA Toyota Trails "Truck Tech" column:

Q: I have a 94 4wd p/u w/ 22re. My engine runs great, except for when it is idling and I depress the brake pedal. The engine then idles really weird, kind of a strong then weak then strong then weak, so on and so forth. It never cuts out, though, and continues to idle normally when I take my foot off of the brake. I've only noticed this after driving, like at a stoplight.

A: Assuming there are no vacuum leaks, such as in the brake booster, it's likely because your idle speed is set too high. I can exactly duplicate this "problem" in my '85 by bumping up the idle speed to a bit over 1000 RPM and it'll act as described. Turn the idle speed back to normal, and it works fine. It's really not a problem, its supposed to work this way and if everything is set properly, and you won't have the "problem".

Why is this the case? Because the ECU has logic built in that says if you hit the brakes and the engine is turning over 1000-1100 RPM, it'll cut the fuel to the injectors in an attempt to help you stop faster. After all, no sense pumping gas into the engine when you are braking to a stop. So idle rises, fuel is cut, idle falls, fuel restored, idle rises, etc. Turn the idle back to

850-900 RPM where it's supposed to be and it'll get back to normal. Idle speed is adjusted with the large slotted screw atop the throttle body. Turn it in to lower the amount of air passing through the throttle body at idle (and thus lower the idle speed).

If you don't want to do that or it doesn't fix the problem, here's a more drastic fix:

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basically involves cutting the wire that feeds the brake light signal tothe ECU. Without that input, the ECU will never know you are braking, so it'llnot be able to cut off the fuel injectors.

-- Roger

Reply to
Roger Brown

Setting the idle down did it, thanks!

Roadie

Reply to
Roadie

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