P0340 and intermittent rough idle
 

Hi,

My friend just bought a 2008 F150 5.4 110k, it ran great all day during all of the test drives, after he gets it home it has started acting up. Most of the time it runs great, but sometimes when you stop the truck the idle will drop down and the truck sounds like it is going to die but so far it hasn't actually died, it starts knocking really badly and runs very rough. If you let it keep running like that it sets P0340. If you rev the truck up it cleans up and sounds fine again and it will even drop back down to a clean idle most of the time. I swapped the cam sensors because it was easy and just to see and it didn't make a difference, I was hoping after switching the sensors the code would switch to the other head but it didn't. Any thoughts? Thanks!

I am thinking probably bad VCT solenoid. I have both cam sensors unplugged and so far it hasn't had any issues since.. I am thinking this points to VCT solenoid. Does that sound possible or is there any other way to test it? Unfortunately since it is an 08 the valve covers have to come off to change the solenoids.

been doing alot of reading on this myself, as i've had a similar issue a couple times as well as a constant, less severe come-and-go bobble at idle. i'm tuning in to see what kind of feedback you get, but from what i gather i think you're on to something.

The solenoids would be a good start. Very known issue with the 5.4 3V engine. If you replace them and still have the issue, then most of the time it is an oil pressure issue. I would do the solenoids first. It may very well cure it.

take a look at my thread discussing my similar symptoms:

https://www.ford-trucks.com/forums/1...ened-once.html

Thanks for the input so far! He took the truck back to the dealer this morning and is going to see if they will take care of him. He will find out on Wednesday whether or not they will either take the truck back or fix it for him. If they tell him he is out of luck which is what I am guessing will probably happen I think we will go ahead and replace the VCT solenoids and see what happens.

please keep us posted either way if you would. cheers!

My son is going through the same thing with his '05 F150 5.4L which was his first vehicle purchase. He hasn't even put 3000 miles on it and just had to replace his tranny and now this is happening. He's so upset...justifiably! He spent all his money on the truck and then on the tranny, there's not much left over for this/these issues. He did just order the VCT solenoids...(oem after reading some of the posts on this thread) and we're keeping our fingers crossed that it works. I just feel so bad for him. If anyone else has any other ideas, please share them as it sounds like this is rather common. Thanks everyone.....FTE Mom

fortunately for him they'll be an easy swap on an '05.

Well the dealer called and told him it needs new timing, whatever that means, I am guessing they want to replace the chains and tensioners and guides and they quoted him $2200. I told him if he can get the dealer to pay for it let them do it but I am not convinced that is what is wrong with it. I would think it wouldn't be so intermittent if it was a problem with the timing components. It also doesn't ever rattle like the tensioners are failing. I am sticking with VCT solenoids being the most likely cause. Am I still on the right track or could a timing issue cause this problem?

Dealer called again and basically told him sorry but there is nothing they can do to help. Probably going to move forward changing the VCT solenoids and hope that does it.

yeah i would definitely try a $200 fix before a $2200!

^ X2 There is no way in hell I would take a $2,200 gamble on an intermittent issue like this. 100% do the solenoids.

Update
 

Update......
Well, changed both solenoids and that didn't fix it. Going to try timing next. Fingers crossed!

@kdawg89


First, I'd never go back to that Dealer you mentioned in post #11. A P0340 code and rough idle - and they tell you that you need new timing chains etc, and then that their is nothing they can do for you... Tell them to F. O.


Then explore several less expensive diagnosis avenues - not necessarily in order. As you said, code P0340 is designated "Cam Position Sensor Circuit Bank 1 Sensor". It is checked / set during the first few seconds of an engine start / run cycle. P0340 Ford Camshaft Position Sensor Circuit Bank 1 Sensor 1 OBDII Engine Light Trouble Code | Engine-Codes.com lists several bazar possible causes for this code beyond a faulty CPM sensor. They include a) Faulty CPM Wiring, b) Faulty Starter motor, c) Starting system circuit, d) Dead (Weak) battery. I have also heard that a bad diode in the alternator can cause noise setting a code 0340, though the alternator will still keep the battery somewhat charged.


According to the Motorcraft OBDII System Theory of Operation Manual - The ECU monitors signals from the Crankshaft Position Sensor (CKS) and Cam Position Sensors (CPM) together to generate ignition / spark pulses at the proper times. Based on these signals, if the ECU does not generate the right number of spark events for each crankshaft revolution - it knows SOMETHING IS WRONG and sets a code. Both these sensors are magnetic (hall effect) sensors and generate weak little signals. Electrical noise or weak signals in these circuits can result in these codes, ie: if the ECU sees EXTRA pulses or MISSING pulses. This can screw up your ignition / spark / timing regularity and other ECU operations resulting in "intermittent" rough idle.


I would check the battery, test the alternator, check/clean electrical connections on CMP's and the CKS - even using a good contact cleaner spray and replug them and make sure the wiring all the way back to the ECU is not damaged, OR WET. (You did mention the problem is intermittent).
You might unplug, spray and replug the ECU connectors.