hey all,
I have read several post about this issue and have tried some of the recommendations. A little history on the problem. Two weeks ago Sun, truck ran fine, however Mon morning all hell broke loose. Truck was running very sluggish and stalling while comming to a stop. My first thought was tune up. I replaced the plugs and wires. during this i found that i could not get a socket around the ever loved driverside rear plug so i was only able to replace 7 plugs however in that process i managed to break the metal coolant tube that runs to the heater core. a day later replaced the entire intake manifold,egr valve, egr tube, IAC valve, both coil packs, fuel filter, tranny fluid and filter. During the removal of the intake i looked at the rear spark plug and found that a screw had been wedged into the hole breaking the plug and got it changed now it is all back together and the truck runs amazing however did not solve the low rpms during stopping. ive replace the above and checked fuel pressure which is good. I have a TPS sensor just havnt installed it yet not sure if it is related to the issue. Tranny guy says it may be a bad soilonoid or TC however last night I reset the PCM and drove it it ran flawless. this morning the problem returned which leads me to believe its not the tranny. ok one last kicker that 6 experts have failed to answer when i manually put the truck into 2nd gear the engine dies! no studder no fighting just quits. sorry for the long post i just want to get all info out there for a solution. truck is a 98 F150 4.6 V8 186,000 miles i have yet to 1) change TPS. 2) clean throttle body. 3) clean MAF sensor. not sure if any of this has an effect on the issue. Oh and there is only a EGR insufficiant Air flow code

 

My first thought was IAC, however you changed that. Is the IAC electrical working correctly? Is electrical plug on IAC completely dry inside? Putting truck into 2nd gear while idling at that low rpm would probably stall out.

 

I did not inspect the connector. It only drops to that rpm while comming to a stop then corrects itself back to the 7 -800 range. the 2nd gear thing is a mystery when i put into 2nd i can mash the gas and it still kills it.

 

So in park it idles correctly?

 

Yes it idles fine in P, R, N, D, and 1. 2 will not stay running and wants to stall stopping

 

These are the results when you don't know how the system works.
The IAC is the key player in the stalling.
Here's how it works on a deceleration:
The TPS is closed down to tell the PCM what is happening.
The vehichle speed sensor also confirms the action by indicating a slowing.
The PCM closes down the IAC to just enough to keep the motor from stalling.
At the same time the fuel is cut back.
Reason is the motor does not need air or fuel on decell.
As the speed sensor nears a slow speed point the IAC comes back open again to keep control of the motor idle.
Any action that does not follow this will result in a stall, rough idle etc.
The IAC has to function to keep A/C and power steering from stalling the motor when they load or change the loading on the motor.
It is also key for cold starts and raised idle.
.
The 401 code is a low flow and should have nothing to do with the stall because it's a separate test and operation.
Low flow means just that. If it were a 402 code then possibly the excess flow might cause rough operation with exhaust gas getting back into the intake.
The only time EGR opens is in OD between 45 and about 65 mph or in third gear at light throttle openings not on decell unless there is a fault..
It is possible for the EGR VACUUM regulator to get dirty and not allow the EGR to close fast enough. Clean it's filter and clean the inside to be sure it does not stick open. What this means is the third port that lets air back into the EGR is blocked so the EGR could hang open some amount of time.
.
It is possible for the converter to lock up it's diode and cause stalling but that's easy to see if the motor chugs nearing a vehichle stop.
It feels like a manuel transmission coming to a stop without putting the clutch in.
Tme to get a Scanner on it and look at the live data and for other codes, as a starting point.
Good luck.

 

so what your saying is the TPS AND VSS could be playing a role in this? I have checked for other codes thats the only one, with exception the 402 has came up once but went back to the 401. I have had the reader hooked up for the last three days watching the live data. thats how i know its droping to the 330 rpms. If it was the converter shouldnt it do it consistantly?

 

Almost sounds like the torque converter is not unlocking when coming to a stop. Possibly a bad solenoid or converter??

 

Thanks. that is what I am starting to think as well everything else is testing out fine. The only thing that throws me off is when I reset the computer It will run fine until it cools back down. seems that it would do it know matter what. i saw another post from 2009 from a feller that had the exact same issue with the stopping and 2nd gear but never replied as to if he got it fixed or not. what makes it real difficult is the fact it isn't throwing codes anymore not even egr since computer reset.

 

its also scary that I have spoke with three tranny guys and all three have nevr seen a vehicle stall when put into 2nd so they just basically say they will tear it down and send bill later. all three recommend a total rebuild do to either a solenoid or converter stating that if those go bad everything will be bad with it

 

Ok all so quick update because i hate when people dont do that.
took truck into tranny shop for indepth diagnostics and the tech said that it is defenatly not tranny related shweew!! however i am back to square one. I will be droping the truck off at a local electric mechanic tonight for further testing i will reply his diagnosis. i have so far replace:

IAC
DPFE
Plugs
wires
egr valve
both coils
evap hose (found burnt in half)
tps
vss
intake gaskets
transmission harness inside
clutch solonoid
shift solonoid
cleaned maff
cleaned throttle body
fuel pressure is 37psi at idle did not check under load
egr code fixed no other codes have came up since

got tired of actual troubleshooting so just threw parts at it "bad thing to do but getting frustrated"

last possabilities are Fuel pump,electrical,ecm,vac leak, maybe even cloged cats but unlikely

Mechanic is going to run smoke test to begin with and go from there

 

Ok Bluegrass 7 this is for you if you do not mind. I can only turn OD off when moving above 35 mph. thats when i feel the rpms raise. After that i leave it off and the truck will run fine until i shut it off again. anyway How does the OD system work? is it normal that you can only turn it off while moving?

 

The Electric Mechanic says yes it is the Tranny/TCC however the Tranny mechanic says its engine related, perhaps electrical. SMH I really do not know where to go from here. my fear is i go ahead and replace tranny for $$$$$$ and it still doesnt fix issue.

 

sorry took it to a differenent tranny shop then original post

 

OD can only engage above about 45 mph as determined by the program in the computer so you can only lock it out above that lower speed when it's engaged.
Yes the RPM will rise because your going back to the transmission normal 1 to 1 ratio with converter lockup.
The RPM difference will be somewhat large.
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If down shifting out of OD occurs under load, the RPM will rise but not as much and the converter lockup also goes off.
In this condition your back to converter fluid slip.
This also raises the transmission operating temperature.
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When you lock out OD while driving it will re engage again on the next time you restart the motor. This is by design so you cannot leave it disengaged unless you do it manually each time.
Good luck.