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Chris (aka- Moose)
Chris (aka- Moose), Mercury Technician
Category: Mercury
Satisfied Customers: 47631
Experience:  16 years experience with Mercury
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Mercury Sable I have a 2003 merc sable which has rough idle.

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I have a 2003 merc sable which has rough idle. above 2000 rpm it seems OK.
Just hit about 100 K miles - it is taken care of well

It is throwing the following codes 4 to my Actron reader.

2003 Mercury Sable Trouble codes
P 1151
Heated Oxygen Sensor Bank 2 Sensor 1 Switch Point Indicates Lean
Lack Of Heated Oxygen Sensor (Bank 1 Sensor 1) Switch, Indicates Lean
System Too Lean Bank 1
System Too Lean Bank 2

1)So which sensor is bank one and bank two - the crappy chiltons manual does not say.
2) What is the best way to test this problem of the rough idle?
3) DO you think one of the O2 sensors being bad will cause this? If so which one? Before or after the cat?

Can I repair this myself - or do I need to take it to the shop - I'm pretty handy - but its really cold outside here in NJ. Could bring it in the garage


Hello, I'm Chris.
I will do my best to answer your question fast and accurate using the info you have provided. Thanks for visiting Just Answer.


Ok there is a front and rear and left and right on your engine, since the engine in your vehicle is in there sideways. When you look at the engine with your belly against the passenger side fender, your looking at the front of the engine. The #1 spark plug is the closest cylinder to the glove box. That is bank one. So if you lean over the fender and touch the engine with both hands. Your left hand will be on bank one and your right hand on bank 2.


Your concern is not a O2 sensor. You have lean issues. You need to start the engine cold and then open the hood and use a can of ether or starting fluid and spray SHORT bursts of ether around the intake gaskets and the air intake tube from the air filter and around all vacuum and PCV hoses. If you hit a leak the RPMS will increase. A lean code means the MAF sensor next to the air filter monitors oxygen coming in and the O2 sensors monitor oxygen in the exhaust. The computer uses the MAF sensor readings to regulate the length of time the injectors spray. So if you have a vacuum leak then more oxygen is getting i n the engine un-monitored and its causing the engine to run with not enough fuel or to much oxygen and the O2 sensors are seeing this, so there telling the computer of the issue and its dumping alot of extra fuel to compensate.


Normally this is just faulty intake gaskets which you may not get a good test on wit h the ether, other possible causes are low fuel pressure or a faulty or dirty MAF sensor.

Customer: replied 6 years ago.
I will try the starting fluid thing ...

I noticed that the idle is fine when the engine is cold- i only goes rough when it get up to running tempature.

How does that effect your diagnosos about fule pressure or vacume leak? Is there something else to check since idle is only reough when warm?

Normally lean codes and vacuum issues are only a concern when cold but I have fixed plenty when hot as well. I would still continue on but place more emphasis on fuel pressure and a MAF sensor concern after the initial vacuum leak check.
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Customer: replied 6 years ago.
could it simply be a clogged fuel filter? Where is that located?
Customer: replied 6 years ago.
I found the leak - it was the PCV ventalator from the intake manifold to the valve cover

Sprayed it with starter fluid and the idle went smooth

It was cracked - taped it and seems to be OK idle now - I will order a replavment part for it
Can you look up the ford part number for me?
Good job, download the base part numbers <<<HERE>>>
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