First let me give you some info. I have a 99 Expy 5.4L. 150k miles with 6 original coil packs and 2 replaced. IAC was cleaned 50k miles ago. New plugs 50k miles ago. Other than that this motor has been maint free.
Sorry so long.
Now the problem 3 weeks ago I hit a deep puddle of water on the passenger side going about 25 or so. Shot water every where. But not sure if the engine compartment got it. I hit it right next to where I worked so just turned in the parking lot and shut if off. After work I tried to start it and it would start and rev up like normal but then die. It did the several times before I gave it alittle gas to keep it going. After a couple of minute it was fine. Ran good and smooth. Did not have the problem again until last week. Same thing got it started and kept the rpms (1500) up for a few seconds and all is fine. Well Friday night it rained real good here all night. Sat morning same thing this time I payed attention to what all the truck was doing. With the A/C on it would not stay running, with A/C off it would run at about 400 rpm. I would get the rpms up to about 1500 and it jumps up to 1900 and back down. So I was trying to see if you would stop. After about 15 min of driving around (30mph) I noticed a slight surge in power and the engine although running smooth seemed to smooth out alittle more and problem gone. Turn A/C on and still no problem. Well it rained last night all night again and I had the same problem and fix this morning. The SES light is not coming on when it is idling low. It seems it only wants to do this when it is real humid and raining. Do you think it is weather related kinda like some of the older distriburated vehicles when the distriburator gets damp. Does any one have any suggestions on what the problem might be. I am trying to get my truck done before FFW next weekend.

I will be changing all 8 coil packs and plugs this week. If any one has any suggestions

 

yeh check make sure your filter doesnt get wet and make sure your IAC is clean its the sensor on the throttle body measures the Intake Air Control. and if the tube that runs to that is clogged or anything or if it gets wet then the engine will rough idle or idle low. or it could be possible coil packs are damaged. but i will ask my dad for anymore sugestions on what the problems could be he knows 1000 times more then what i know cause he works for ford for 19 and now works for a generator company.

 

Anyone else.

Pretty Pleaseeeeeeeeeeeeeeeeeee

 

My guess is you got water in the spark plug holes...

You might try to get the codes read anyway. I've seen some instances of misfiring but no code gets thrown.

Good luck in any case

 

if its a constant miss your check engine light will come on.

 

You can get the codes read for free at Autozone so its not like he would lose any money to get it checked.

 

There is no miss. When it is running at the low rpms the engine run smooth. When the rpms comes back to normal there is still no miss.

 

Get the codes read. If it idles at 400 rpm there should be a code. How deep was the water? I play in the Mud/Water and all my engine compartment connectors have been coated with dielectric gease. In the futur you may want to consider this.
Let me know what the codes are. Something is wet and has not dried out.
Do you have any mods done to the truck?

Regards

Jean Marc Chartier

 

The water sprayed like in your sig but just from one side. Maybe 10" or so deep. When I change out my coil packs i will make sure to coat the connections.

Thanks to all for the help.

 

JMC yes I do have a few mods. Superchip tuned by JDM, JDM e-fan, cobra r water pump, ftvb and drop in K & N. I have run these mods with the exception of th ftvb for nearly 100k miles with no problems.



The problem started before the ftvb was installed.

 

A guy here at work had the same problem. Same exact symptoms. It finally stopped on its own. Probably a wet connection somewhere. My quess is either the IAC valve or Throttle Position Sensor. Check the wire connections there first.

 

I just wanted to know the mods to see if any of them could be affected by water intrusion. I don't think the Mods themself would have caused the problem. It would seem like the IAC is not letting the truck idle properly. Check the connector on the IAC. Your IAC should be located behind the Throttle body. I would remove it too and clean it if it hasen't been done. I would also check the PCV system for a crushed hose and the valve itself.

JMC

 

Thanks JMC. I will be replacing the coil packs tommorrow w/plugs and will pull the IAC and clean that as well and check the connector. JDM will be here in Houston I am gonna try to get him to data log the truck as well.

 

IAC IAC IAC IAC IAC IAC IAC IAC IAC

I had the EXACT PROBLEM, with out the puddle. Parked it running fine, and next time i started it, it WOULD not idle. once I did get it to idle, after holding the pedal down and letting it warm up.. it idles aroung 350-400 RPM. I took it in as this was just after i bought it USED they cleaned th IAC and it's been great since,

 

i had the same problem for a while. i never had the SES light come on but i read the codes and it showed coil #3 was acting up. i pilled the coil and found the boot was cracked and damp. i replaced the coil and boot and havent had a problem since. knock on wood