Check engine light / rough idle

[davem]

On my 2001 XLT, V-6, approx 85K miles ..........

About a month ago, I noticed rough idle sometimes at start up, check engine light came on, and stayed on for a few weeks. The the CEL went out.

I've had rough idle at start-up several times lately, and yesterday the CEL came back on.

I had the code scanned, P0306, which could be vaccum, fuel pressure, ignition, and a 4th item I can't recall.

After several miles of driving the idle seems to be about normal. But I have the problem on just about every cold start.

Any suggestions ?

Thanks

Dave

 

[Firestorm]

Were you getting any other codes besides the P0306? The Haynes manual says that this code is a "Cylinder #6 misfire detected". How long has it been since you've changed plugs and wires?

Also, you may check into cleaning your MAF, and IAC.

 

[davem]

Were you getting any other codes besides the P0306? The Haynes manual says that this code is a "Cylinder #6 misfire detected". How long has it been since you've changed plugs and wires?

Also, you may check into cleaning your MAF, and IAC.

I was not informed that any other codes were read.

I think we tried new wires and plugs when I had my previous P0306 2 years ago - it was the fuel pressure regulator.

I suppose it could be wires/plugs - there are original (85K miles on a 2001).

Would they tend to be a problem at start-up, that goes away when warmed up ?

 

[Firestorm]

Hmn. How about cleaning the MAF and IAC? Not really too sure if spark plugs and wires have a difference when they're cold or not. I believe I would try to clean the Idle Air Control valve though, this may help. It is used primarily at start up.

I'd say someone else here has alot more information to give than I can.

 

[gavin]

I'm getting a similar issue, but on cylinder 7, not 6.
Sometimes it idles very rough, sometimes smooth. Although mine generally seems to have a smoother idle until it warms up.
Haven't replaced the plug wires in quite some time, so gonna pick up a new set tomorrow. Already replaced the plugs.

possibly the coil pack.

 

[ThePhoenix]

let us know if wires fix the problem...

 

[gavin]

well mine was definately plug wires.
after replacing 'em, I decided to test the cyl. 7 wire, per Chiltons, for giggles.
resistance was zilch; not 0, non-existant. There was a break in the wire somewhere apparently.
my truck's running the smoothest it has in months!

 

[wrigley_1285]

I had the same code come up on my 00 Sport. It was because one of the plug wires had started to ware out and the wire was showing. Couldn't tell because how the wires are ran from the factory under the intake(poor design IMO). Put some new Bosch plugs and wires on and it fixed it right away. I ran my wires over the engine so I could keep an eye on them and prevent it from happening again.

 

[Firestorm]

Good job you two. How about you Davem?

 

[ThePhoenix]

i have wires on the way. I will let you know if that solves my codes P0171 and P0174 lean

 

[Firestorm]

Did you ever try changing your intake manifold gaskets, Phoenix?

 

[ThePhoenix]

not yet! I have been hampered money wise by my wife being out of work. I so think the PO neglected to do any maintenance in the last months he owned it, so I am starting there. all I have really done is the spark plugs and cleaning the sensors.


but wife just got some money...so I ordered plug wires. and I am thinking of doing my ball joints this weekend.

if it still runs rough, I will change my intake gaskets and get it looked at for sensors

 

[Firestorm]

I understand what you're going through. I also thought that you and I were having the same problem. I changed my plugs and wires, and it didn't help a bit. I picked my gaskets up at Auto Zone. They were $14 and some odd cents. Not really a tough job to do, just make sure you take your time. Hope you get it running better soon.

 

[ThePhoenix]

thanks. Maybe i will tackle that in the next two weeks

 

[Firestorm]

Let us know how it goes.

 

[davem]

Good job you two. How about you Davem?

I took it to the local Car-X. They cleaned the MAF, tested for intake gasket leak, etc.

I'm still having the problem.

Guess I'll try cleaning the IAC. Can someone point me to a picture showing where the IAC is located on a V-6 4.0 (2001 XLT) ? I assume its under the black plastic shroud that has the 4.0 SOHC on it ? Or is it somewhere else ?

(I'm looking for a device held on by two 10mm bolts, with an electrical connection.

Thanks.

 

[Firestorm]

You are correct, it is right below the SOHC shield. Did you ever try changing your spark plugs and wires?

 

[davem]

You are correct, it is right below the SOHC shield. Did you ever try changing your spark plugs and wires?

I cleaned the IAC tonight with carb cleaner. It did not look really dirty to me, but was not sure what to compare it to.

The sping flexed. The diaphram moved when I wiggled it up/down. In the 'default' position, it was what I consider 'slightly open' - not sure if that is normal.

I re-installed and will see how it goes tomorrow morning as I try a 'cold start'.



2 years ago, when the same P0306 was resolved with a new fuel pulse dampener, they tried new plugs/wires, which did not resolve the problem. I suppose they could have failed in the past 2 years. (2001 XLT with 85K miles)



I keep thinking its a fuel/vaccum/sensor issue since its only a problem on a cold start.

 

[gavin]

may even just try resetting the computer.

can't hurt anyway :scratch:

 

[Firestorm]

Yes, which I forgot to mention. You should disconnect the negative battery cable for atleast 10 minutes. This will reset your computer. Vehicle may suck gas afterwards as it relearns it's normal operation.

It may be another fuel pulse dampener, Davem. Someone with more experience than me should chime in.