LOW IDLE
Thread Starter
|
Cross-Country
Joined: May 2011
Posts: 75
Likes: 0
LOW IDLE
My '88 EFI 460 has never idled well. Usually lower than 600 rpms. Just rebuilt the motor and trans.No vacuum leaks. Runs lean, never hits cold idle(factory 1200 spec, mine 8-900), drops idle when coming to stop or going RND/DNR 400 to near stall. Pulled the codes for MAP sensor/replaced, EGR clogged(only 1 year old and changed out for new), checked O2 sensor(w/in specs), TIP specs w/in specs. All emissions plumbing was replaced. This is at the point of what I know what to do. Any guesses or known solutions.
Elder User
Joined: Sep 2018
Posts: 735
Likes: 8
From: NC
Proper temp / properly operating thermostat? Radiator cap working correctly? Engine coolant sensor good? O2 sensors been checked?
Has the adjustment screw on the IAC been messed with?
Just brain storming here...
Has the adjustment screw on the IAC been messed with?
Just brain storming here...
Thread Starter
|
Cross-Country
Joined: May 2011
Posts: 75
Likes: 0
O2 sensor good. I disconnected the coolant sensor to see if the idle would adjust higher as per cold running cycle and no change. Didn't see an adjustment screw on the IAC. Pressure tested cap. I know that are no real adjustment for this system. Reminds me of the late emission carbs. Didn't have much to adjust and the adjustments never worked.
Cargo Master
Joined: Jun 2013
Posts: 3,182
Likes: 15
From: Somewhere n North America
Unplug the Air Bypass Valve/AIC, see if it make a difference. RPM should drop down some, or even an engine stall.
It is also a good Idea to remove this valve, spray it down with Carb cleaner & replace with new gasket.
Zombi, I think is talking about the "Throttle Stop Screw" on the Throttle Body...
It is also a good Idea to remove this valve, spray it down with Carb cleaner & replace with new gasket.
Zombi, I think is talking about the "Throttle Stop Screw" on the Throttle Body...
Cargo Master
Joined: Jun 2013
Posts: 3,182
Likes: 15
From: Somewhere n North America
You should have seen a ECT code when this is disconnected.
Disconnect the ECT, and measure the resistance across the 2 pins of the sensor.
Go to the site via link below, compare you location temperature to the resistance your cold sensor should be.
Say it's 50 degs F. where you are working on your sensor, the sensor resistance should be around 45K ohms, 45,000 ohms. If it is not close to the comparison resistance, then it is out of range.
Ford Fuel Injection » Engine Coolant Temperature Sensor (ECT)
Cargo Master
Joined: Jun 2013
Posts: 3,182
Likes: 15
From: Somewhere n North America
How did it idle before you rebuilt the engine ?
Trending Topics
Cargo Master
Joined: Jun 2013
Posts: 3,182
Likes: 15
From: Somewhere n North America
Create a small vacuum leak to see if the idle raises.
like, disconnect the Speed Control or HVAC/Air handling vacuum line from the Vacuum Tree.
Don't use the MAP, FPR, PVC or Brake hoses.
like, disconnect the Speed Control or HVAC/Air handling vacuum line from the Vacuum Tree.
Don't use the MAP, FPR, PVC or Brake hoses.
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
Elder User
Joined: Sep 2018
Posts: 735
Likes: 8
From: NC
Unplug the Air Bypass Valve/AIC, see if it make a difference. RPM should drop down some, or even an engine stall.
It is also a good Idea to remove this valve, spray it down with Carb cleaner & replace with new gasket.
Zombi, I think is talking about the "Throttle Stop Screw" on the Throttle Body...
It is also a good Idea to remove this valve, spray it down with Carb cleaner & replace with new gasket.
Zombi, I think is talking about the "Throttle Stop Screw" on the Throttle Body...
Cargo Master
Joined: Jun 2013
Posts: 3,182
Likes: 15
From: Somewhere n North America
Yes, old carburetor lads who had no clue about the new EFI systems...
Thread Starter
|
Cross-Country
Joined: May 2011
Posts: 75
Likes: 0
I had the injectors tested prior to the rebuild and they were w/in range. I just removed the new EGR and plugged the hole and got 200-250 addition rpm.If this works I might for go w/o one. I know that it is counter intuitive but that cooler exhaust gas coming thru the EGR cools down the charge entering the combustion chamber. W/O one it might ping. Maybe premium gas will be the answer.
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
You just found the problem I think, the EGR should not be open at idle. Is there vacuum on the line to the EGR valve at idle? Again there should not be so if there is either it is mistakenly hooked up to manifold vacuum or the EGR vacuum regulator is malfunctioning.
Thread Starter
|
Cross-Country
Joined: May 2011
Posts: 75
Likes: 0
Water got into the ECM. Was packed with dielectric grease. Cleaned it , dried it and installed it. Running better. Anyone have a source for that rubbery/foam grommet that the cabling runs from the motor to the ECM?
Thread
Thread Starter
Forum
Replies
Last Post
NotMatt
1987 - 1996 F150 & Larger F-Series Trucks
16
Jan 8, 2025 05:58 PM
Boss_Hogg
1987 - 1996 F150 & Larger F-Series Trucks
18
Jan 21, 2019 06:56 AM