I replaced a bbk 65mm throttle body with the stock unit (bbk part was defective) and now with the stock tb I have a really low idle. When I come to a stop idle drops to 750 then 720 then 680 and almost sounds like it's going to die but once gas is applied runs fine. I also had the IAC valve replaced with a new motor craft part, would it be possible the IAC is bad as well? Before I replaced the IAC and stock tb truck ran perfect.

 

Make sure the IAC plumbing isn't pinched or kinked.

Can't think of anything else that would cause this, except the IAC getting stuck.

 

Whoever put on the aftermarket throttle body might have done other mods as well.

Also, did you remove the battery cable and allow it to relearn idle?

Also, maybe you left something unplugged. I've done that with the air temp sensor a time or two.

And maybe you left a vacuum line unplugged or accidentally knocked one loose.

Lots of simple stuff you could double check.

 

Thanks guys, I left out possibly a important piece of info. The ABS light has been coming on and off for a couple weeks now as well. Brakes are all new, could it possibly be VSS sensor? Truck has 156,000 on it and the sensor has never been replaced

 

That's got nothing to do with the idle, though.

Check your alternator and battery voltage before you go too far...

 

Throttle trim needs relearned. Look up Ford Tech Makuloco on youtube, he has a video on the procedure and an explanation.

 

I did do the relearn two different times when I got the truck home, same problem after both

 

You didn't say that. Didn't you say in another post that you bent the springs and such?

 

That was first thing I did when it started running like crap, my throttle return spring is slightly stretched (could that cause this issue?) I went to a pick a part to look for a new one but no v10 tritons anywhere

 

My truck idles on the Scangauge above 670 all the time, when I had a misfire a couple weeks ago it would drop to the 620's and stumble. Your numbers don't seem off. Does the TPS require calibration during installation?

 

So my idle problem was a loose throttle cable coupled with where the bracket lined up with the linkage, Mechanic adjusted it and now idles between 720 - 750, also replaced all the spark plugs (all 10 were toast) also replaced PCV (also toast) and replaced the battery.

So I now noticed that the truck when it stumbles and goes quite for a second happens when coasting to a full stop when it goes from 2nd to 1st it sometimes drops 150 rpm then balances out, also happens very slightly when it goes 3rd to 2nd.

Would this be a torque converter/trans problem? My trans has been heading downhill for the last 6 months, loss of power going up hills, can hear the clutch spinning when hitting the gas uphill and it pops between 1st to 2nd shooting me forward most take offs from a full stop.

 

Ok so I think I was wrong and it's not the transmission, truck still drops rpm when I stop, used my air conditioning today and it completely corrected the problem. Any ideas?

 

CEL on?

Only things that come to mind for me are a canister vent solenoid or fuel pump on the outs.

The canister vent would be accompanied by a P1450 code. I've had both of these solutions to the symptoms you describe on 5.4 SDs.