vehicle idling rough after restart

[JAWIT]

Been having this issue with the 08 Mountaineer V6 for a while now. Vehicle has about 120K on the clock and when I start vehicle after it has been sitting overnight or even for a few hours, it will idle just fine. However, after running the vehicle for a while, if I turn the engine off and then restart say 5 to 10 minutes later, it will idle very poorly like it is wanting to stall. If I rev the engine a bit, the problem clears up and the idle is great. It also never occurs again until I turn off the key and restart while the engine is still warm/hot.

The spark plugs and wires are new, MAF has been cleaned less than 1,000 miles ago. I also sea foamed the vehicle through the brake booster last year. Fuel filter was replaced, as well as air filter.

Recently, I noticed that the RPMs jumped a bit when going up a slight incline, and power seemed slightly low, but not sure if this is related to idle problem.

As far as I know, the idle is controlled by the computer, since I don;t think there was an IAC valve for the 08 model year. Could it be a vacuum leak? There are no stored codes according to my mechanic and they could not find any issues at all. I know this issue has come up before on the forum, but I couldn't find a definitive answer on the problem or how it was resolved, if at all.

Thanks for help in advance.

JAWIT

 

[Jordan4461]

JAWIT-
My Exploder is a 2008 4.0 liter with 200,000 miles on it. It stumbles occasionally after a restart, like yours. I end up giving it a a little gas to raise the revs, and it lines back out. Mine gets 20mpg on cruise at 70mph, and has plenty of power. It doesn't have any vacuum leaks, so I figure it is either the computer or the MAF sensor, which has been cleaned. It was much worse prior to cleaning the MAF sensor. With 200k on the clock, I won't waste money chasing gremlins or replacing the MAF sensor to overcome a stumble that is fixed with a stab of the gas pedal
Jordan

 

[JAWIT]

Thanks Jordan. I might try a bottle of Chevron Techron to see if that helps. I read that some folks replaced the Throttle Position Sensor (TPS) but if mine was faulty, I'd expect that it would throw a CEL. Others manually cleaned all injectors to help fix the problem.

 

[96eb96]

Maybe try that seafoam aerosol spray into the throttle body. There are professional services that can do this too with a pressurized bottle (you can buy it too but need a compressor). There is no IAC but there could be some carbon deposits on the throttle plate or valves.

 

[98Hooptie]

leaking injector symptoms

 

[JAWIT]

Thanks for your replies on this. Mechanic cleaner the throttle body and MAF, but I know i did that sometime last year. We'll see how it behaves.

 

[gmanpaint]

Sounds like a bad temp sensor for the ECM. When these go bad, the computer doesn't know the proper air to fuel mix to use, and the engine runs rough when already up to temp, on a restart.

There should be two temp sensors. One is just for the dash gauge, and the other is for the computer (ECM).

 

[JAWIT]

Hopefully not the temp sensor as this was just replaced last year when I had a new aluminum thermostat housing installed.

 

[JAWIT]

So the throttle body and MAF cleaning did not solve the problem. Would the aluminum thermostat housing retain heat better than the stock plastic one? I thought perhaps that it was fooling the temp sensor into thinking the engine was hotter than it really was. Once over the slight idle issue, it runs fine.

 

[07EddyB]

leaking injector symptoms

That would be my vote.

 

[JAWIT]

Would this be solved only through physical removal and cleaning of the injectors or replacement? Will something like Techron clean them well enough or is this temporary?

 

[07EddyB]

Would this be solved only through physical removal and cleaning of the injectors or replacement? Will something like Techron clean them well enough or is this temporary?

I really don't know. I'm only responding because you are obviously responding to my post. I have not yet had any problems with my injectors so I don't really know how to troubleshoot that particular issue.
The first thing I would do is to hook a scanner to it and get real time misfire data from it. It would seem to me that if you have a cylinder flooded with gas then it would register a misfire on that cylinder due to the way that it measures a misfire.
I might also drive it and then pull the plugs and look for a wet one.

 

[98Hooptie]

Would this be solved only through physical removal and cleaning of the injectors or replacement? Will something like Techron clean them well enough or is this temporary?

Your results may vary but ive never seen a "leaking" injector benefit by any fuel additive. Now if the injector spray pattern is caused by dirty injector then the cleaner will help with it "sometimes".

 

[JAWIT]

I'll need to research this further as I don't feel I know enough about how the leaking injectors contribute to poor idle. Especially if there are no symptoms at any other time. It doesn't occur every time the vehicle is restarted and very much appears to be temperature related.