High Idle at Startup
Tuned
Joined: Jul 2002
Posts: 479
Likes: 12
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.
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.
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.
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.
Logistics Pro
Joined: Dec 2003
Posts: 3,776
Likes: 862
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.
It has been that way for 12 years now.
Temporarily Deactivated
Joined: Aug 2003
Posts: 1,859
Likes: 2
Originally Posted by yardbird
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.
It has been that way for 12 years now.
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.
Post Fiend
Joined: Feb 2004
Posts: 10,728
Likes: 1
From: Damascus-Boring, Ore
loud clunk or clang
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.
New User
Joined: Aug 2004
Posts: 10
Likes: 0
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.
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