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post #1 of 2 (permalink) Old 04-27-04, 09:07 PM Thread Starter
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adjust idle on '93 5.0 t-bird?

Hello, all. My apologies if this is a stupid question, but I'm new here so I'll give it a shot.

A few days ago, my car started idling VERY high (>2k) in neutral/park, it accelerates (or at least maintains speed) without the accelerator down, and braking is a chore... a friend suggested adjusting the idle down, but we couldn't locate a simple idle screw on the throttle assembly. Anyone out there that can point me to the right procedure?

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post #2 of 2 (permalink) Old 05-18-04, 04:45 AM
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Re: adjust idle on '93 5.0 t-bird?

Hi, you do have a idle screw, but no the procedure for adjusting isnt that simple and it probley isnt necessary anyways unless you already played with it. The idle is self adjusting via the idle air control valve, which is computer controlled.
I'm guessing you might have a vacuum leak, and i think i might know where to look, from memory the windsor trucks were famous for a high idle which came from leaky gaskets at the throttle body or at the back of the intake plenum.
A 93 bird has a similar gasket at the upper plenum, even though the plenums appear much different in height, and i'm not sure, but didnt it have the same dual throttle body gasket around 93 as the 351 or 302 truck motors too??
It doesnt cost anything or take much time to carefully spray any sort of upper intake or carb cleaner from a aerosol can (use the straw) in the area of the suspected vacuum leak and listen for a change in idle, if it changes theres the leak. Dont use anything like silicone spray, it could damage the O2 sensor.
Try also other areas that seal the intake and around injector o rings if necessary.
Of course tps sensor, iac valve or even processor could possibly be the trouble.
But if the car idles high all the time even when first restarted thats a huge clue towards vacuum leak.
If it idles high, but you turn the key off (erases kam) and then it idles low after engine restarted its possibly a tps problem or related. This is due to the fact that the tps sensor resets its base idle reading(rewrites to kam) to wherever its at when the key is turned on (not while cranking) regardless of its position. I can prove and explain this to anyone who's interested in a future post.
Also if its idling high through a vacuum leak, you will probley get a code while you do a self test with the engine running, i forgot the number of the code, but the definition will be that the computer cant lower the idle to a low rpm level or something like that.
So just pull the connector of the iac valve and see if the idle drops, the computer has probley closed it mostly anyways to compensate, so if you pull it off and it still idles considerably high, you can also then be sure its just a vacuum leak.
Also, make sure accelerator cable is still routed correctly and not possibly pulling throttle open slightly.
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