Idle and Idle Up adjustments

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Idle and Idle Up adjustments

Postby JohnT » Tue Jan 13, 2004 10:32 pm

There are a number of adjustments that can be made to the throttle body, it is easy to get mixed up as to which is which.

The idle adjustment is a small brass set screw on top of the coolant heated section at the back (firewall side) of the throttle body. This is the only proper way to adjust the idle speed.


2)Idle up adjuster:
The idle up solenoid actuates a vacuum diaphram, which then drives a throttle stop  on the driver's side of the throttle body. This has a small philips head screw, set in a shroud, that adjusts the amount of idle up you get when the idle up controller kicks in. To adjust, turn on the headlights, the idle up relay should kick in, and adjust the screw so that the rpms are no more than 1100 to 1200.  If you screw this in too far, the idle up box cuts out, makingthe engine hunt up and down.

3) Throttle plate stop

At the rear of the throttle body there is a screw, set in the factory and yellow painted to stop you adjusting it. This screw is only to prevent wear on the throttle plate, and should not be used to adjust slow idle revs. It should just touch as the throttle is shut down, allowing the throttle plate to fully close, yet taking the force of the mechanism shutting down. Use of this screw to adjust slow idle will result in poor slow running stability.

Hunting - revs go up and down by themselves:
The common causes of hunting seem to be:
1) Vacuum leak (post throttle) such as a cracked vacuum line to MAP sensors.
2) Worn or misaligned throttle plates (unlikely to be seen unless you pull the throttle body apart)
3) Air bubble in the top of the cylinder head coolant exit. Let air & small amount of coolant out of the bleed nipple to eliminate any air near the TW sensor.
4) Poorly adjusted idle up mechanism (idle up clicks in and out)

John T

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