Too Lean Air/Fuel mix

I have a 1999 contour se sport 2.5 DOHC. (i like it when people are specific)

I had a problem a little while ago as you could see back i had to replace the IAC on this car. When the IAC was messed up I kept getting the Too rich code on the ODB-II reader. Now I replaced the IAC and also gave it a tune up. I put the Bosch Platinum II plugs in it. About 2-3 days later the light came on and the reader said that both banks (1 & 2) were running lean. Is this in contribution to the new spark plugs or do you think I have another problem? Thanks in advance for your help.

First of all, the bosch platinum plugs are definetely not recommended for the duratec V6. This topic comes up at least once a month on CEG so I'll let you read why.

http://www.contour.org/ubbthreads/showflat.php?Cat=&Board=perf&Number=112598&Forum=perf&Words=bosch%20platinum&Match=And&Searchpage=0&Limit=2500&Old=allposts&Main=112496&Search=true#Post112598

Definetely not a spark plug problem. If it were the plugs, it would be a rich code since they would be giving an insufficient spark.

What did your tune up consist of?

What kind of an air filter do you have in the car? If it's an oil charged filter toss it and clean your MAF (Mass Air Flow) Sensor.

I have a 1999 contour se sport 2.5 DOHC. (i like it when people are specific)

I had a problem a little while ago as you could see back i had to replace the IAC on this car. When the IAC was messed up I kept getting the Too rich code on the ODB-II reader. Now I replaced the IAC and also gave it a tune up. I put the Bosch Platinum II plugs in it. About 2-3 days later the light came on and the reader said that both banks (1 & 2) were running lean. Is this in contribution to the new spark plugs or do you think I have another problem? Thanks in advance for your help.

Maybe a vacuum leak somewhere allowing unmetered air into the combustion chamber.

where can I get the motorcraft platinum 2 plugs? Is this straight from the dealer?

The air filter is not oil charged but taking apart the rest of the air intake the MAF is okay but behind that there is some noticeable oil on the bendable hose, like it is coming out of one of the breathers from the valve covers.

where can I get the motorcraft platinum 2 plugs? Is this straight from the dealer?

The air filter is not oil charged but taking apart the rest of the air intake the MAF is okay but behind that there is some noticeable oil on the bendable hose, like it is coming out of one of the breathers from the valve covers.

Yes, from the dealer.

Oil is normal after the MAF since the PCV vents into the accordian tube.

Okay, i'll get some new plugs and try to see if I can find an air leak. Maybe I didn't get the bolts for the IAC all the way tight.

You can buy Motorcraft plugs from just about any aftermarket parts house.

found 1 of the bolts loose on the IAC. When i replaced it must not have got them all the way tight. Changed plugs but plugs did not change the way it runs. Cleared the codes, i'll see if it comes back.

if indeed there was an intake leak at your IAC, that would certainly cause the lean code you were getting.

2.5 L has a problem with intake manifold gaskets that leak
if you can read data stream from your code reader look at long and short term fuel trims while spraying brake clean around intake (both upper and lower) gaskets , i'm sure you will see them change if they change usually go all the way negative , this is very common , replace both sets of gaskets
also Ford has a TSB on lean and rich issues related to the MAF sensor which is also very common

I haven't had a problem with it now all week. Think we got it.

Thanks guys