high mileage 1999 4.6 4wd 5 spd: Needed to replace the rear ABS sensor and decided to clean the throttle body too while the battery was unplugged. Cleaned it around the butterfly and not much else. Truck idled at 750 BEFORE cleaning the TB. Now it fluctuates between 820 and 950 rpms. Also tends to stay at a higher rpm after pushing in the clutch and taking it out of gear. Did a thorough check for vacuum leaks, nothing. Not throwing any codes. After research, I cleaned the IAC and re installed (battery was disconnected then too). No improvement. Unplugged the IAC while running- ZERO change in idle. Installed new IAC, no change whatsoever. Unplugged NEW IAC, no change whatsoever.
Is there an issue with the PCM needing time to fully re learn? Am I missing something (besides the 40$ for the IAC)?

 

Has it finished drive cycles? Mine did same until drive cycles completed and computer readjusted.

 

Good question. How long is a "drive cycle"? What does it consist of? I've idled the truck for several minutes till it warmed up. Lights on, heater, radio,heater fan, all on to load the system. Drove it a mile or two, came home. Hot started it 3 or four times. Still idles in the 800's. One thing I can assure you, I sure as *&^% ain't gonna unplug the battery again. Total BS.

 

I usually finish drive cycles within about 3 days of normal driving habits. It'll return to normal.

http://www.obdii.com/drivecycleford.html
or
http://www.fordscorpio.co.uk/drivecycle.htm

If you have an OBDII reader, you can see if there are open monitors yet to be completed.

 

Oh! Cool. I will give it a try. I have a Scan Gauge Ultragauge that allows me to monitor certain things but it isn't a proper scanner. The "quick Learn" method of driving the truck won't speed up the process?

 

When disconnecting your battery, you have to drive through the whole RPM ranges, from stop to highway speed (shifting gears), etc so the truck can "relearn" how to properly drive. I would assume a 20 or so minute around town and back home would get it. Maybe a few punches of WOT?

 

Thanks for the input. Put over a hundred miles on it since the battery disconnect. No help. I'm still looking....

 

Maybe you knocked off a vacuum hose?

 

I did a vacuum check with a can of carb cleaner a couple of times, truck never bogged down. Even disconnected and reconnected all the vacuum hoses that would have been affected. No change.Kind of at a loss right now but I do appreciate everyone's input.

 

Unless you are watching a scanner while spraying the carb cleaner, you most likely be will not able to notice any fluctuation in the idle, the computer is just fast for that. That will work on old school engines, but not so much now.

Did you remove the TB to clean it? Something is leaking air to make it idle high. Have you scanned it for pending codes, if you did what is pending?


The fact that there is no change with the IAC disconnected makes me think it's sucking extra air from somewhere. Re-double check all your connections and vac lines. My bet is it will through a lean code pretty soon.

Hope you get it soon and it is easy, good luck.

 

You cleaned it on the engine didn't yuh ? You burned some holes in the PCV system tube. That's a very big reason why Ford says NO HARSH chemicals in the throttle body. If you sprayed carb cleaner in it, your lucky if you can still drive at all. Just the over-spray/fumes can smoke the TPS ribbon link. Truck can't shift correctly when that happens.

The throttle body IS NOT a carburetor. Something like that will do quite a bit of damage to the top end...IAC malfunction included. It won't work right after burning up the plunger bushings. Take it all apart to determine the extent of the damage done.

 

Pending codes are p0113 and p1504, both related to an unplugged IAC (which is brand new and never been exposed to harsh chemicals). The throttle body was cleaned on the engine. Truck was not running during the cleaning and the harsh chemicals were sprayed onto a lint free rag that was then used to clean the gunk out. Truck is a manual 5 speed and shifts nicely. My TPS is sending a good signal to the scan gauge so that doesn't seem to be an issue. Again, I appreciate all input and once I do find out the problem, I will definitely post what the problem was.

 

Yea, if you can view those DTC's, they're not pending in a sense you may be thinking. All that means is the problem is there, what's pending, is you fixing it.

Appreciating is one thing, acting on it is another. Since everything has been covered, -time for you to do something.

BTW- Yes, please post the problem, honestly if you can.

 

Lets take the time to go over how to describe an issue.
1. Describe accurately what is happening along with any codes.
2. Do not include any long history because what is happening now is what's important.
3. Do not fall back on what parts or work was done weeks or months ago 'that could not be an issue'.
4. Do not ask whys or what ifs on the problem trying to second guess it before the trouble is solved for.
5. Do not rely on 'it looks good', be sure.
.
We need the above to have any chance of accurately providing diagnosis, then you need to carry out the suggestions and report the results.
This is the help you come to ask for and how it is rendered.
Good luck.

 

Normal idle:
1. It is set in program as 650 +/- 50 rpm.
2. The cranks sensor is the engine Tach that reports the RPM to the PCM.
3. The IAC modulates the idle air stream by bypassing air around the throttle plate under PCM control, to keep the idle 'within' the program table.
4. Throttle plate has some intentional opening set in by throttle stop as base air so the IAC has a range to work over, for idle control without stalling.
.
If high idle is present with the IAC non operational and closed, there is air entering extra air entering at some point to raise the RPM. It cannot be any other way.
These 4 stroke engines run on air flow with a 'little' gas mixed in.
More air, more power and RPM, it's that simple. Same as you do with your foot on the peddle while driving.
Good luck.