My 2001 f150 supercrew 5.4 4x4 has a rough idle and sometimes goes dead, no check engine light is on. Usually happens when it is very cold outside <32 degrees, truck will start, then go dead, won't start the first time, start and then blow out black smoke. Acts like its loading up like an old carburated engine.

 

How many miles?
How many on the spark plugs?
IAC ever been cleaned?

 

97,000 miles spark plugs never changed were is the iac located

 

does it matter if you apply 50% gas pedal(pulses the injectors) or if you apply 100% gas pedal (fuel cut off)?

Could be the IAC, could be MAF sensor too. You could have a big bug on the MAF that is pissing off your PCM.

IAC is right next to the throttle body, pull it off and let it sit there still connected, turn on ignition and attempt to start engine. You should see some changes in the position of the pintle. If NO and NO to that.... I would look into a fuel pump or fuel injector leak down problem.

 

when given throttle the truck revs normally, as if nothing is wrong

 

What solved this problem?

 

It's a pretty common problem. 9 out of 10 times it's the IAC valve.

 

When these IAC valves first start to act up, sometimes you can resume the normal idle speed by cranking the engine until it fires, then as quickly as you can, snap the gas pedal to the floor. As whatever goes wrong internally gets worse, this is less effective.

As close as I can tell, something seems to be grounding out inside the solenoid. I'm on IAC #5 right now. With pins inserted into the backside of the harness the bad valves flunk the ohms test, usually.

Dave

 

Here is what happened. 2001 F150 100k miles, K&N filter,

The truck was working properly. While idling it died. So I started it back up and discovered a very rough idle with black smoke. Limped it home. The next day it worked fine. But the next day it again had a very rough idle with black smoke.

No codes have thrown yet.

So far I have:
1) cleaned the MAF with CRC Mass Airflow Sensor cleaner
2) cleaned the TB and butter fly 1.5 inches on either side the the butterfly.
3) sprayed brake cleaner on vacuum hoes to try to detect an unseen vacuum leak.

Have been told that the ECT: Engine Coolant Temperature, is a likely candidate for this problem. I do have a new one to put in.

Any other advice or suggestions. I realize that with out a proper scanner I'm shooting in the dark a bit.

 

clean out the iacv. a poor mans diagnosis tool is to disconnect a sensor one at a time and see if it runs better......

 

You know, I'm beginning to think there may be a problem at times with the PCM and trouble codes.

Keep in mind that I had NO codes shown when scanned, either with OBDCOM or Actron. The problems were definitely there however. I resorted to testing every single sensor and electrical component that might have an effect. This is what I found:

TPS- no code tripped, but with volt meter attached to ref. wire/grnd., the voltage did not increase as the throttle was opened. Replaced the TPS.

IAC's #1 thru 5- No code tripped, but with back probe with pins/multimeter, they all flunked either ohms or voltage. Replaced them all. These were all done over a 5 year period.

EGR- The EGR pipe was rusted off inside the heat shroud, and the truck did have some extra exhaust noise, but I thought that was the gasket (which was blown out from rusted off bolts). The EGR couldn't have been working, but, no code. Replaced the pipe/flare fitting, tested the EGR.

Coils (2)- Although they tested a little high for secondary resistance, I left them in.

End result- The truck runs like new again ( I think, but I didn't buy it new, so maybe not). Steady 19" vac. (200,000 mi.)

Just my 2 cents. But relying on scan tools won't always help.

Dave

 

Thank you for the quick replies.

Update:

Forgot to say that I did look at the IAC. It was clean and had no build up inside it. But I did not spray any cleaner into it.

This morning, returned SuperChip setting to default setting. Truck start up just find. Smoked a bit, I'm assuming cleaning out the overload of fuel.

Then ran 1/2 can of SeaFoam through the brake vacuum. I was surprised - there was smoking of any kind - I guess that is a good sign?

Also put 1 can in the gas tank. Then took a drive for 25 miles at about 60 miles an hour.

Any insights?
Did setting resetting factory defaults "reprogram" the PCM?

Dave, Where is the best vacuum port to test from? And are there 5 different IAC's?

 

I made a TEE with a plastic fitting and a couple of short pc's of hose, and attached that to the throttle body housing (passenger side). There was, on mine, a vac gang fitting to pull off and insert the TEE. It's the most accurate way because the EGR & EVAP vac comes from the same gang fitting. Once I noted vac at this port, I could remove the TEE and individually check each small line for the same reading.

It can take 2-3 driving cycles, after making a repair, for the PCM to recognize and use the new data. This is with the code erased (if you had one displayed).

No, there are not 5 different IAC's for a given application. I meant I've had 5 go bad ?

Dave