High Idle at Startup

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Aug 28, 2004 | 10:26 AM

#16

byronbgs

Tuned

Joined: Jul 2002

Posts: 479

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From: Louisiana

Mine does the same thing. It's more pronounced since I changed the fan clutch. But it's at 1500~ RPM right after I start the truck then goes to 1K~ then to 600-700 RPM.

I installed a Sun Pro tach earlier this year from Pep Boy's $30.

I have noticed that if I give a tap on the gas that it will knock the idle down quicker.

Quote:

Originally Posted by polarbear

Yep- my '93 5.0 does the same thing (always has, come to think of it). I like to wait for the idle to settle down before I shift it into gear, though. I imagine I'm saving the tranny a little grief. Laugh if you want, I'm still running the original 4EOD @ 190K miles.

I shift into Drive first to get the juices flow in the tranny then to Reverse. I have been having a loud clunk or clang sometimes when I would shift into reverse at a faster idle.

Aug 28, 2004 | 12:47 PM

#17

93candycane

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Joined: Dec 2003

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The tap on the gas will idle it down right away but that is also when it seems to drive sluggish. So long as I let it idle down on its own it will drive great for me.

Aug 28, 2004 | 01:11 PM

#18

yardbird

Logistics Pro

Joined: Dec 2003

Posts: 3,780

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From: Foothills of NC

I took care of the 1500 rpm cold idle on my 87 4.9. Not everyone will approve, but it works for me. I disconnected the electrical connection to my IAC, and adjusted the set screw on the throttle plate to where it idles at about 950 rpm. It will still go up to about 1100 when cold, but much better I think than reving to 1500 when it is 15 deg. outside and the oil is thick and not flowing good.

It has been that way for 12 years now.

Aug 28, 2004 | 05:34 PM

#19

HardScrabble

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Joined: Aug 2003

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Quote:

Originally Posted by yardbird

There are instructions in the manual telling you to do this. You need no approval.

If I have an idle problem I usually look for vacuum leaks. Most old trucks have a vacuum leak or two, it never hurts to track down a couple.

Listen to other trucks start-up and see if they sound like yours.

Aug 28, 2004 | 11:46 PM

#20

polarbear

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Joined: Feb 2004

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From: Damascus-Boring, Ore

loud clunk or clang

Quote:

Originally Posted by byronbgs

I shift into Drive first to get the juices flow in the tranny then to Reverse. I have been having a loud clunk or clang sometimes when I would shift into reverse at a faster idle.

Makes sense- but check the bolts on the transmission crossmember- could be the source of that noise.

Aug 29, 2004 | 12:24 AM

#21

couleeman

Posting Guru

Joined: Jan 2003

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From: Magrath

Check the ect sensor. If you want more of a reason why, ask tommorow when I sober

Aug 29, 2004 | 03:53 PM

#22

byronbgs

Tuned

Joined: Jul 2002

Posts: 479

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From: Louisiana

Quote:

Originally Posted by polarbear

Makes sense- but check the bolts on the transmission crossmember- could be the source of that noise.

Thanks polarbear i'll check the bolts

Aug 29, 2004 | 06:10 PM

#23

custom88

New User

Joined: Aug 2004

Posts: 10

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From: Kansas City Missouri

The throttle plate stop adjusting screw on my 88" 4.9L EFI I-6 was set so as to allow too much air to bypass the IAC valve resulting in a high idle and this was accentuated during the ECM's warm up cycle. I simple set the throttle stop at 1/4 turn of the set screw.