idle issues
Thread Starter
|
Freshman User
Joined: Sep 2010
Posts: 45
Likes: 0
idle issues
Hello everyone I have an 01 f150 4.6 4x4 automatic with 90,000 miles. I have an eratic idle but it only happens when I am on the freeway well actually when I get off the freeway and stop. the idle will fluctuate between 750and then drop to 400 then back and forth til I get moving again. I replaced the IACV because it was doing the weird humming and vibrating the intake tube. the humming is gone but still idles funny as stated above. any and all help is much appreciated.
Thank you
Thank you
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
The IAC is still suspect.
You can't have an idle issue when moving or on the road at speed because the throttle opening is beyond the idle stage.
The IAC has no control when the throttle is open to power the vehicle at road speeds.
.
What happens when you slow from road speed is the IAC goes closed and fuel injection cut.
As low rpm comes down and road speed slows to a near stop the computer opens the IAC and adds some fuel to recover the idle.
You normally never feel an issue from this action unless there is an issue.
.
If cold start is ok and normal idle is stable, there may be a hose or fitting air leak that opens up under high vacuum at slow downs with throttle closed. Under these conditions the PCM could idle hunt for a time trying to recover stable idle.
It does this by comparing the crank sensor rpm indication with an idle table in program to control the IAC until it matches the table within +/- 50 rpm.
So you see there is a lot that goes on during the drive cycle in software and hardware control just to keep idle smooth and improve fuel mileage.
.
Good luck.
You can't have an idle issue when moving or on the road at speed because the throttle opening is beyond the idle stage.
The IAC has no control when the throttle is open to power the vehicle at road speeds.
.
What happens when you slow from road speed is the IAC goes closed and fuel injection cut.
As low rpm comes down and road speed slows to a near stop the computer opens the IAC and adds some fuel to recover the idle.
You normally never feel an issue from this action unless there is an issue.
.
If cold start is ok and normal idle is stable, there may be a hose or fitting air leak that opens up under high vacuum at slow downs with throttle closed. Under these conditions the PCM could idle hunt for a time trying to recover stable idle.
It does this by comparing the crank sensor rpm indication with an idle table in program to control the IAC until it matches the table within +/- 50 rpm.
So you see there is a lot that goes on during the drive cycle in software and hardware control just to keep idle smooth and improve fuel mileage.
.
Good luck.
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
After replacing the IAC you should consider rebooting the PCM because it still has the old data in memory from the idle issue and will need to relearn if the IAC was the problem.
Replacing a part that operates under the control of the PCM is not an instant change/fix because memory is involved that needs to also change.
The only way is to clear and reset all the tables contents back to baseline values for relearning.
Best way to begin relearning is to start with a cold motor start. Let run with headlights and heater/A/C motor running until it is fully warmed.
This procedure make it a worst case load on the whole system so the PCM learns to handle it.
Then shut off, do hot restart and drive a few miles and do several more hot restarts to maximize the alternator loading on the motor so it learns to handle this as well.
Other wise it will relearn over a longer period as you use the truck.
Good luck.
Replacing a part that operates under the control of the PCM is not an instant change/fix because memory is involved that needs to also change.
The only way is to clear and reset all the tables contents back to baseline values for relearning.
Best way to begin relearning is to start with a cold motor start. Let run with headlights and heater/A/C motor running until it is fully warmed.
This procedure make it a worst case load on the whole system so the PCM learns to handle it.
Then shut off, do hot restart and drive a few miles and do several more hot restarts to maximize the alternator loading on the motor so it learns to handle this as well.
Other wise it will relearn over a longer period as you use the truck.
Good luck.
Tuned
Joined: Jan 2022
Posts: 274
Likes: 12
Does anyone have the actual Motorcraft part number for the IAC and TPS ? I see different part numbers online and I'm not sure which one to get.
94 f150 5.0 extended cab rwd automatic. Any help greatly appreciated.
94 f150 5.0 extended cab rwd automatic. Any help greatly appreciated.
Trending Topics
Tuned
Joined: Jan 2022
Posts: 274
Likes: 12
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
Thread
Thread Starter
Forum
Replies
Last Post