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Revs Drop When Headlights Are On?

thirtythree-II

By thirtythree-II,
in General Maintenance

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thirtythree-II

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The revs drop from 700rpm to 500 rpm continously on idle, but only when the headlights or foglights are on. As soon as I turn them off the R33gtst stays on a nice idle of 700rpm.

Im tippin it's either the battery needs replacing or the alernator..... has anyone encountered this problem before?

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RB30-POWER Mentor

RB30-POWER

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Well the alternator will be putting more load on the engine whilst pumping out higher amperages to run all the lights etc.

However, the AAC valve should bypass more air around the throttle to raise idle to 700rpm.

I would say your AAC valve is disconnected or not working at all.

Another test will be, turn all the lights off, but whilst on idle/parked, turn your steering wheels full lock and see if the idle drops as well.

As its doing basically the same thing as the alternator, putting load on the engine that the AAC valve should be compensating for.

thirtythree-II Collaborator

thirtythree-II

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I replaced the battery, and what do you know, still have the idle problem!

I guess i'll have to find an AAC valve off a wrecked R33 and replace the existing one.

Is it a simple bolt off and then on with the new one. Any gasket needed?

RB30-POWER Mentor

RB30-POWER

Posted
Posted (edited)

No gasket needed.

Its got a brown connector/plug on it at the rear of plenum chamber. (Near the hose that runs to the brake booster)

It may be faulty, or it may not be plugged on properly or it may have a broken wire between the ecu and valve.

If you measure the connector with the ignition on, it should have +12V on one of the wires, and the other wire runs to pin 4 on the ecu, the ecu pulses the valve to ground to control how far it stays open.

You could even, connect a 12V battery to the aac valve when you get it off the vehicle and see if it opens with power applied. (Its a solonoid so the plunger will pull in when you connect 12V to it)

I would check the valve first before just replacing it.

Edited by RB30-POWER

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