06 5.4L V8 Lariat Low RPMs under load/Stalls when stopping

[Dwillhauck22]

2006 Ford F-150 Lariat 5.4L V8 Flex Fuel With 221,000 Miles

The issue i am having is that when you come to a stop the rpms drop down into the 300's. This sometimes leads to it stalling out, especially if I just tap the gas and then hit the break right away. If i slip it into neutral the rpms return to the factory range of about 600-700. But as soon as I put it into gear and there is a load on the engine they drop to the high 400 low 500s. I just replaced both the camshaft position sensors hoping they had something to do with it but no luck. One thing i noticed tho is when the truck does stall out the low oil pressure warning lamp comes on and it takes an extra second to fire back up. But after it is running again oil pressure is at normal range. I have an Edge CTS 2 unit so I am able to monitor all of my engines data from fuel rail pressure to intake air temperature and everything in between. Hopefully someone can give me a solid direction to look in so im not on a wild goose chase trying to hunt down the issue.

P.S - I have a DTC for Bank 2 efficiency below threshhold, I have a bad cat and its been bad for a few years without casuing any driveability issues. I have also noticed that the problem gets worse as the engine reaches operating temperature. Any and all input is greatly appreciated. Thanks

[65comet]

Before you said bad cat, that was what I was going to suggest. The cat can clog up so bad that it takes away all the power at idle fighting against the back pressure. If there is a mechanical connection before the cat, I would try disconnecting it and see if it relieves the pressure and lets you know that is the problem if it runs fine after that. The pressure can become so great that other exhaust recirculating components can fail and even explode under the pressure.

[Dwillhauck22]

Originally Posted by 65comet

Before you said bad cat, that was what I was going to suggest. The cat can clog up so bad that it takes away all the power at idle fighting against the back pressure. If there is a mechanical connection before the cat, I would try disconnecting it and see if it relieves the pressure and lets you know that is the problem if it runs fine after that. The pressure can become so great that other exhaust recirculating components can fail and even explode under the pressure.

The CAT has been that way for a while without causing any issues. Also there is no loss of power when I really get on the throttle. I would think that if it was the CAT causing the issue because its restricting exhaust flow that signs and symtoms of that would be present at times other than idle. It drives fine and it still has plenty of get up and go for an old truck with over 200,000 miles. I have been doing research and so far the best thing I have come up with is the Variable Camshaft Timing Oil Control Solenoid or VCT Solenoid. Could this be a probable cause of the issues I am having? Appreciate the input.

[65comet]

My 05 before it came out how bad the Cam phasers were, I replaced the VCT's because that was at the time thought to be contributing factor in those symptoms. I do know the new ones from Ford are many times better than the original and wouldn't hurt to replace them for that number of miles, even if it didn't solve the issue. Hate just throwing parts at a problem, but this is something it probably needs and could take care of it.

[Dwillhauck22]

Ya there is a lot of things on the truck that are in need of replacement at this point in its life. As much as I hate guessing and throwing time and money into trying to fix the issue these are things that are in need of replacement anyway. The VCT solenoids that it came with from the factory are prone to cloging and causing a host of issues. Ford redesigned the solenoids so they are less susceptible to cloging and failing in the future. I just ordered the parts online and will have them tomrrow. As soon as I get them I will throw them in and pray that they were the issue. If not I am just going to bring it to the dealer to have it diagnosed unless someone on the forums can give me a better idea about what else could be causing the problem.

[Dwillhauck22]

Here is a quick update with where I am at. I replaced both of the Camshaft Position Sensors with a good improvement in how the engine runs and a major reduction of the amount of valve ticking the engine is known for. Unfortunately no luck with the RPM issue tho. Then I went and replaced both of the VCT Sensors, this showed major improvement on how the engine runs and the remaining valve tick has been completely eliminated. One thing I noted while replacing the VCT Solenoids was that on one of them the screens on the bottom portion of the solenoid were gone and are presumably in my engine somewhere. I am hoping that since they were made of a fragile plastic and a very small metal screen that my engine chewed them up and caught them in the oil filter. If it didn't then I am wondering if they may be still inside the engine and clogging up an oil port somewhere causing my issue. Any input and ideas are greatly appreciated. Thanks.

[Dwillhauck22]

Problem solved!!! Luckily it wasn't a faulty torque converter or transmission or clogged oil port. I pulled my throttle body off today and it was packed with soot and grime. Took me almost an hour with a plastic brush and 2 full cans of throttle body cleaner to finally get it cleaned. Re-installed it, cleared the DTC’s and disconnected the battery for 5 minutes to clear active memory and took it for a long enough drive to get it up to operating temperature and to get the oil temperature at maximum and the RPMs remained steady in the 550-600 range without dropping. So after spending hundreds on new camshaft position sensors and VCT solenoids all I needed to do was spend $10 on throttle body cleaner and spend an hour cleaning it. Thank you to everyone who posted their 2 cents!