03 4.6 V8 Idles rough in cold weather, no drivability issues.

[zerodevil]

Hello,

As the title says my 2003 v8 will start fine in cold weather (20 Degrees and colder) run fine for a few minutes, and then start to sputter, massive RPM drop, its 50/50 weather it catches or dies out. this happens randomly every 2-5 minutes even at operating temperature ranges. Has recently had COP's replaced, new spark plugs, and a new motorcraft IAC. The truck runs and drives excellently, and plenty of power.

truck has exhaust, headers, Cold air kit, plenum, and a 93 octane tune.
Any ideas?

 

[SyberTiger]

No CEL engine codes?

I'm just throwing it out there....

Harmonic Balancer on it's way out causing vibrations and shaking?

 

[boominXplorer]

Check the rubber pcv elbow and see if its crushed in or deteriorated.

 

[zerodevil]

NO CEL Codes shown on FORSCAN, How do i check the damper? Idle is smooth, until it decides to fall on its face randomly.

the PCV elbow is in good shape, are you thinking vacuum leak?

 

[lincolnshibuya]

does it die on idle?

 

[SyberTiger]

It'll likely throw CEL codes if it's a vacuum leak based on the description you gave of the problem.

With regard to the harmonic balancer...with the engine running and it shaking try to look down at the balancer to see if it looks like it's wobbling. If it's good it should appear to be turning very smoothly. Another idea....maybe one of your belt pulleys is on it's way out and every once in a while it get wobbly. Take the belt off and spin the three tension pulleys, plus the belt tensioner pulley, plus the p/s pump pulley just to make sure the bearings turn smooth and also check for wobble by pulling back of forth on each side of the pulley.

 

[zerodevil]

Not a rough idle problem, idle is strong and smooth, But randomly the truck will suffer a massive drop in rpm (from 750-800 down to 350 ish) and at that point its 50/50 if it will catch itself and recover or die at idle. also happens when coming to a stop at traffic lights and the likes.

Strange thing was we noticed that when the hood is open that this problem goes away, Though maybe bad filter, cleaned filter, and with the filter removed tried to idle the truck with the hood down. the problem was back, opened the hood and it smoothed itself right out. as a last ditch effort we unplugged the MAF sensor, truck idles and drives like a dream with the MAF unplugged. Removed the MAF and ran a whole can of MAF cleaner over the two sensors and saw no improvement. We are thinking we have a faulty MAF sensor at this point. Seeing as how those are not cheap we are going to let a mechanic diagnose to be certain.

Thanks for the ideas guys.

 

[graphitegreg]

Not a rough idle problem, idle is strong and smooth, But randomly the truck will suffer a massive drop in rpm (from 750-800 down to 350 ish) and at that point its 50/50 if it will catch itself and recover or die at idle. also happens when coming to a stop at traffic lights and the likes.

Strange thing was we noticed that when the hood is open that this problem goes away, Though maybe bad filter, cleaned filter, and with the filter removed tried to idle the truck with the hood down. the problem was back, opened the hood and it smoothed itself right out. as a last ditch effort we unplugged the MAF sensor, truck idles and drives like a dream with the MAF unplugged. Removed the MAF and ran a whole can of MAF cleaner over the two sensors and saw no improvement. We are thinking we have a faulty MAF sensor at this point. Seeing as how those are not cheap we are going to let a mechanic diagnose to be certain.

Thanks for the ideas guys.

Seems a bit late now but I was thinking electronics such as that as my wife's vw did the same thing ad we found a code indicating as such afterward.
Good luck

 

[SyberTiger]

It is possible your new IAC is defective...it does happen. I had a new Motocraft IAC crap out after11 months as I recall. The MAF should not have anything to do with idle. Maybe try the propane test to check for vacuum leaks....If a 2008 comes with the rubber elbow then check and recheck it and I mean take it off and inspect it...not a cursory looksie with a flashlight.

 

[zerodevil]

The new IAC was installed as a result of this idle issue. The truck is scheduled to goto the shop this upcoming friday, i will update with answers once i hear back. My 2003 is not daily driven so i can afford to let it with out much issue.

I didn't have access to propane for the vacuum test but i used carb cleaner on all hose joinings, fittings, and elbows and noticed no change in idle. Both elbows coming off of the valve covers are in great shape, as are all of the hoses.

 

[boominXplorer]

It sounds like you have a 3v phaser issue but you say its an 03 so its only a 2v. What is you battery voltage cold vs warm? These v8s do all sorts of crazy things when the alt starts going out and won't even show a battery light.