weird idle

Reply Subscribe

Thread Tools

Search this Thread

Jan 14, 2019 | 08:05 PM

speedybill

Thread Starter

Trailering

Joined: Nov 2014

Posts: 16

Likes: 0

weird idle

99 F350 dually 2wd
V-10, 200,00 miles
Idle goes up & down, sometimes it will stall,
no codes, cannot find any vacuum leaks, going to replace PCV valve,
any ideas?

Jan 14, 2019 | 10:54 PM

R&T Babich

Fleet Mechanic

Joined: Feb 2011

Posts: 1,812

Likes: 88

From: Thousand Oaks, CA

Quote:

Originally Posted by speedybill

99 F350 dually 2wd V-10, 200,00 miles Idle goes up & down, sometimes it will stall,
no codes, cannot find any vacuum leaks, going to replace PCV valve, any ideas?

Also, check your IAC - Idle Air Control valve.

Jan 15, 2019 | 11:06 AM

krewat

FTE Leadership Emeritus

Joined: Jul 2002

Posts: 42,561

Likes: 421

From: Long Island USA

Sounds like a stuck IAC - the computer is trying to control the idle and can't.

Jan 15, 2019 | 04:42 PM

V10man

Logistics Pro

Joined: Feb 2000

Posts: 3,955

Likes: 47

From: Mesa

I've had 2 IAC valves go bad, one on a V10 and another on a 4.6L. neither threw a code.

Jan 17, 2019 | 04:21 PM

speedybill

Thread Starter

Trailering

Joined: Nov 2014

Posts: 16

Likes: 0

Thank The the help.
II picked up an IAC.
Can I take the throttle body off to make it easier to replace it?

Jan 17, 2019 | 06:13 PM

R&T Babich

Fleet Mechanic

Joined: Feb 2011

Posts: 1,812

Likes: 88

From: Thousand Oaks, CA

Quote:

Originally Posted by speedybill

Thank The the help.
II picked up an IAC.
Can I take the throttle body off to make it easier to replace it?

You can, but there is a gasket between the throttle body and the intake that might need to be replaced.
The IAC has no input to the PCM so there would be no codes for it.
The throttle body butterfly plate completely closes at idle and the only way the engine gets any air is thru the IAC valve which is controlled by the PCM.

Jan 18, 2019 | 08:39 AM

speedybill

Thread Starter

Trailering

Joined: Nov 2014

Posts: 16

Likes: 0

Thankx
I'm going after a gasket for the throttle body.

I'll let ya know how that goes.

Top 10 Ford Truck Tragedies

Joe Kucinski

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

Jan 18, 2019 | 04:12 PM

R&T Babich

Fleet Mechanic

Joined: Feb 2011

Posts: 1,812

Likes: 88

From: Thousand Oaks, CA

Quote:

Originally Posted by speedybill

....I'm going after a gasket for the throttle body. ....

While you have the throttle body off inspect the throat below the butterfly for gunk.
Clean with carb cleaner if needed.
I remember a post where idle/running issues were caused by a layer of gunk down there.