Freaking high idle
Thread Starter
|
5th Wheeling
Joined: Jan 2023
Posts: 25
Likes: 3
Freaking high idle
1996 f150 4x4 4.9 efi
idles 200 -300 rpm high than normal at operating temp
No vacuum leaks test every way possible(smoke,brake clean,carb clean,propane, stethoscope)
New iac valve
New tps
New vacuum lines
New every fing gasket
10° advanced timing
spotless throttle body
Engine warms up to 90 Celsius (canada) so 194 f
At idle @operating temp I can disconnect iac valve with no change to idle at all
pedal linkage does not have downward pressure at idle
no codes
New injectors
So my next though o why is a worn out throttle body bud it didn't seem to bad, a bit of light at the bottom left of one of the butterfly valves, can any one post a pic of what a good one should look like so i can compare visually. Also butterfly valves do have the holes in them which i have read some people block off to get normal idle ? Last thing i have not checked is the maf sensor may pull and clean thoughts?
idles 200 -300 rpm high than normal at operating temp
No vacuum leaks test every way possible(smoke,brake clean,carb clean,propane, stethoscope)
New iac valve
New tps
New vacuum lines
New every fing gasket
10° advanced timing
spotless throttle body
Engine warms up to 90 Celsius (canada) so 194 f
At idle @operating temp I can disconnect iac valve with no change to idle at all
pedal linkage does not have downward pressure at idle
no codes
New injectors
So my next though o why is a worn out throttle body bud it didn't seem to bad, a bit of light at the bottom left of one of the butterfly valves, can any one post a pic of what a good one should look like so i can compare visually. Also butterfly valves do have the holes in them which i have read some people block off to get normal idle ? Last thing i have not checked is the maf sensor may pull and clean thoughts?
Hotshot
Joined: Jun 2015
Posts: 12,783
Likes: 2,422
Well…that’s not right. The idle should come down when you disconnect the IAC.
Thread Starter
|
5th Wheeling
Joined: Jan 2023
Posts: 25
Likes: 3
Idle has been high since I bought the truck, and yes I have check codes none present checked with quality scanner not a cheap one. As I said I have checked for vacuum leaks every which way you can none present
Logistics Pro
Joined: Nov 2013
Posts: 3,922
Likes: 1,192
From: Mojave, Ca
Did you disconnect the IAC and then back out the screw? If you mess up the screw setting, theres no consequence. Just Reset it to "barely touching" plus one or two turns. Theres a real Ford procedure, but adjusting it like a carburetor works.
Trending Topics
Thread Starter
|
5th Wheeling
Joined: Jan 2023
Posts: 25
Likes: 3
Hi to be honest when I when trying to see if the screw would affect thing no I didn't disconnect the iac first. Should i try with the iac disconnected?
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Fleet Mechanic
Joined: Aug 2015
Posts: 1,827
Likes: 358
From: Candy Mountain
In order to adjust the set screw the engine needs to be warmed up and the IAC needs to be disconnected. If you can get it to something around 700 rpm shut it down re-connect the IAC and restart it and see how it behaves. If you are happy then run KOER testing and see if the computer is happy with its ability to control the idle rpm's. It will report a code if it doesn't like what you did.
If you can't get the idle to come down then you have a vacuum leak that you will need to address before you can reset the set screw.
You can eliminate most of your accessory vacuum systems for testing by pulling them off the vacuum tree and capping the ports. The only ones you have to have are the FPR and MAP.
Hand actuated vacuum pumps are the best way to check vacuum circuits and components.
If you can't get the idle to come down then you have a vacuum leak that you will need to address before you can reset the set screw.
You can eliminate most of your accessory vacuum systems for testing by pulling them off the vacuum tree and capping the ports. The only ones you have to have are the FPR and MAP.
Hand actuated vacuum pumps are the best way to check vacuum circuits and components.
Logistics Pro
Joined: Nov 2013
Posts: 3,922
Likes: 1,192
From: Mojave, Ca
Follow R&Rford's recommendation. Including testing each vacuum circuit with a hand vacuum pump if the Idle screw adjustment doesnt work.
Fleet Owner
Joined: Oct 2005
Posts: 20,784
Likes: 1,751
From: Kentucky
Hotshot
Joined: Jun 2015
Posts: 12,783
Likes: 2,422
With the IAC connected, the computer was making adjustments while you were turning the throttle stop screw.
Thread Starter
|
5th Wheeling
Joined: Jan 2023
Posts: 25
Likes: 3
So tinkered a but last night, got ut up to temp disconnected the iac and turned out the idle adjustment screw no change. Pulled and capped/plugged lines off of the vacuum tree one at a time, the pcv line when capped did drop the idle to 750 so I will pick up new pcv valve today. Question should the pcv allow air flow to the intake, basically having a bit of a hard time wrapping my brain around how it's supposed to function. Since it's under vacuum from the intake would it not always allow air to go from valve cover area to the intake since the poppet under vacuum will unseat?