Hey everyone, I'm new here. I usually lurk around on forums but am stuck on this one. I recently picked up this 95 4.9 e250 (125,xxx miles) at a government auction for 200 bucks. They said that it needed a head gasket but that wasn't the case. I think that they got tired of trying to figure out the problem and was getting on the old side for the school district so they just said that to get rid of it. I was able to peak at the service records real fast while I was there and right at the end before taking it out of service they put in a new computer, plugs, wires, rotor and cap, coils, eeg.

When I got it home it had a slight miss to it every 10 seconds or so. Other than that it idled perfectly fine and seems to rev fine in park. When its in Drive or Reverse it stumbles hard, very hard. KOEO test comes up with 111 but when I do a KOER test at first it came up with a 411 code. I ended up replacing the throttle body gasket, cleaned the throttle body, replaced the TPS and the IAC with new parts. The miss went away after the throttle body gasket but the hesitation under the load is still there. A week goes by and figured I try replacing the Computer just to see as I have 2 extras laying around. Neither of those changed anything. I ran another self test and this time it came up with a 412. I went through all the checks with IAC testing for resistance and voltages and everything seemed fine. Lastly, I have 3 total IAC valves and plugged them all in with the key on I could feel the solenoid get voltage but couldn't see anything move. When the engine is running and I unplug the IAC the RPMS do not change.

Seems like most people that have this problem, clean or replace the IAC or the brain and problem fixed. But not this one.
Does anyone have an idea where I should go from here? Thanks for any help!

 

I forgot to mention that after all the items tested out good (brain, wire harness and IAC, it still won't change the idle when the connector is pulled after its started. I've tried 3 IAC's and 3 brains total with no change. Only thing I didn't try extra was a new harness as that doesn't look all that fun to change. 1 IAC is brand new. 1 Brain is suppose to be brand new but I'm only going by their records. 1 other brain came from ebay out of a supposedly good running van and the last one was pulled out of the junkyard. Any ideas?

 

I worked on it today again. 411 code kept coming back up. Took it out for a drive and when in drive but the brakes on it idles fine. When take foot off the brake, it hesitates until it gets going. Then it seems to drive fine. The IAC still doesn't drop the idle when I unplug it while it's running. However I looked at prodemands website if any of you are familiar with it and they have about 8 different checks with the IAC, Computer and wires to check it. Everything seemed to check out fine.

Wondering does anyone know, if I leave the IAC unbolted but plugged in. When I turn the key on I feel the solenoid engage but the rod doesn't move at all. It didn't move on all three that I checked. So I tried 3 IAC and 3 computers. Not really sure where to go from here.

 

My guess is you have improper air flow set.
In other words someone has turned the do not turn screw on the throttle body and you have the throttle plates open.
And that would make the IAC valve unable to adjust the rpm.
Note if you back off the screw too far the plates can stick.

Is this the eight they gave you?
DTC 411 indicates that during Engine Running Self-Test,
engine rpm could not be controlled within the Self-Test lower limit band.
Possible causes:
-- Improper idle air flow set.
-- Vacuum leaks.
-- Throttle linkage binding.
-- Throttle plates open.
-- Improper ignition timing (Distributor Ignition vehicles only).
-- IAC solenoid contamination.
-- IAC circuit short to ground.
-- Damaged IAC solenoid.

 

Thanks Subford for the response. Those were not the 8 checks I did. Mine was just related to the IAC and computer. I checked them twice so I think I can rule that system as working. What I checked was:
1. Measured IAC solenoid resistance
2.Check for internal short to IAC solenoid case
3.Check VPWR circuit voltage
4. Check IAC circuit continuity
5. Check IAC circuit for short to ground
6. Check IAC circuit for short to power
7.Check IAC signal from PCM

So I think I ruled out the IAC system itself. I've looked for vacuum leaks over and over as I thought that was the problem at first. I suppose there still can be one but I'll move onto crossing off the idle screw that you mentioned.
So out of the list below that you mentioned, as of now, I'll rule out 2,6,7,8. So if I'm working on number 1 - improper idle air flow set. From what I read is that the throttle stop screw MUST be touching the linkage. Mine looked fairly close but I believe it wasn't touching when I looked at it last time. Is there a set procedure that you find better or correct for setting the idle air flow setting? Also since the linkage isn't touching the throttle stop screw, I could probably rule out number 4 unless I suppose there was contamination still in it, correct? Thanks for all your help and response so far.
1-- Improper idle air flow set.
2-- Vacuum leaks.
3-- Throttle linkage binding.
4-- Throttle plates open.
5-- Improper ignition timing (Distributor Ignition vehicles only).
6-- IAC solenoid contamination.
7-- IAC circuit short to ground.
8-- Damaged IAC solenoid.

 

There is a procedure for setting the screw and it is very detailed so most just put a meter on the TPS and turn the screw until they get 0.9 VDC.

 

Ok thanks, I'll have to look for this procedure. I'd rather do it the correct way unless even if it's detailed and a pain. Unless you think the TPS route is a just as effective route. Seems like you are a go-to guy on here so I'll trust your decision on that. I don't mind putting the work into getting it fixed the correct way. Thanks Again.

 

I would go by the procedure.

 

See attached PDF.

 

Thanks, Will this be the same procedure for the 4.9?

 

The 4.9, 5.0 & the 5.8 should be the same.
The 7.5L is different as it uses Procedure B.

 

Thanks, I was overlooking the test procedure and looks like I'll need a Star tester? Is there a way around that or is that the only way? I have one of those yellow code readers but if a star machine will be handy maybe I'll try to find a cheap one.
Thanks again for all your help.

 

All I can do is post the two procedures from the 1995 Ford Shop manual.
Note the procedures below may be different than the posted one above.

For procedure "B".
(1) In some cases, even if idle rpm is OK, proceed with this procedure if customer symptom
persists (Idle Air Control (IAC) duty cycle may be out of range).
(2) Key Off/Restart/Recheck
idle for two minutes (eliminates possibility of entering part throttle mode).

 

Well I don't have a star tester but someone else mentioned in another form to try and put some tape over the holes in the TB valves. I did that as well as checked the TPS voltage. That was spot on. The other person also mentioned that if the voltage from the white wire at the IAC while idling needs to be 9.5vdc- 10.5. If over then there's a vacuum leak. Mine is 11.7. Anyways I plugged the holes with tape, didn't change the hesitation when putting a load on it however the code reader came back with a 111 each time I ran it. I started another thread with timing issues I seem to be having. Not sure if I have multiple problems, or one is causing all of these. Any ideas?

 

SOLVED: I just wanted to post this here since this is a common issue with lots of possible solutions as it seemed when I searched. I finally figured out the problems so I just wanted to let people know what I found so they may not have to go through the same headache I went through. My main problem with the bucking/hesitation when I put it in drive or reverse ended up being the PSOM unit. The yellow capacitor had come loose on one joint. I simply reconnected it and fix my main issue. Someone in another forum that I found in 2004 said to simply disconnect the PSOM from the back of the cluster and see if the problem continues. If it doesn't obviously this is probably your issue as in my case.
If I remember right I sometimes had gotten a 213 code. I ended up swapping the ICM from a junkyard part and it worked fine. The symptoms were missing. I only noticed it after I fixed the PSOM unit as they blended into each other.
I was getting a 411 code for a long time. Not sure what ended up fixing that as it seemed like it came back every now and then after fixing it all but haven't gotten it for a while now.

Another issue I think I had was my fuel regulator and maybe my pump. I can't say for sure since I was using a harbor freight testing gauge that turned out to be bad. I am pretty sure at least my FPR was bad.

Last issue was my brake booster. It held vacuum fine. But I could hear a swooshing noise when I pressed on the peddle. The brake would feel pretty good and stopped but would go too far in. I replaced the booster and the problem went away.

Anyways I just wanted to update this thread in case anyone in the future has my same problem and maybe this might help them.
Thanks for the help everyone.