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Discussion Starter #1
Two days ago I changed my oil and oil filter, and cleaned my air filter on my AEM CAI. The next time I drove my car it idled very rough and it seemed like it wanted to stall. It has yet to stall but it gets very very close. Today, driving on the highway, I noticed when I would go down large hills the engine temp would actually go down. This has never happened before. Granted, it was about 33 out and raining hard, but I think I've driven in similar conditions and don't remember it ever doing that. It also idled rough again today. It also seems to buck a little bit here and there when in gear.

Any ideas on what could be wrong? The only thing I can think of is I might have overfilled oil slightly, I can't check right now but will be able to tomorrow. Even if it is overfilled it would only be slightly. The car holds 4.5 quarts, that's what I put in, and right after filling and running I checked the dipstick and it seemed to be right on full.

Any other ideas? Could cleaning the air filter screw up the mass air flow sensor enough to cause this?
 

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hmm...is there an air leak somewhere along your air intake system? i had a similar problem when using my old CAI. check along the CAI tube for leaks. even the smallest leak could trough off the sensor if it's after the MAF. you wouldn't want leaks in the system anyways to check that.

also, the rough idling could be a bad tank of gas. alot of people think they have a problem when actually they don't, they just filled up with a take of gas that wasn't as you are use to. my advice would be fill up again at another gas station and see if this problem persists.
 

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did you let your filter dry before you oiled it and then let the oil soak in before you put it back on the car? If not it might have got "junk" on your MAF sensor.
 

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Discussion Starter #4
Actually, I thought about the bad gas tank too because I have gotten bad gas before. I did fill up again and same problem. Normally when I get a bad tank, it may run rough for a few seconds and then fix itself, maybe running rough a few times during the life of the tank. This seems to do it more than 70% of the time when idling.

I will check to see if there are any air leaks though.

As for oiling the filter, my filter does not need to be oiled and it dried overnight before I put it back on. I will check the MAF sensor though too tomorrow.
 

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as for the ruff ideling and bucking, your fuel pump might be going on it get it checked it should be around 40psi, it just happened to mine, how many miles do you have on your car?
 

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yea it dont matter how many miles are on your car a fuel pump can just go. i only have 74k on mine and i had mine just done. take it to a ford dealer and ask for a 9920 you pay like a 100 buck and they will tell you exactly wat is wrong with your car and if is the fuel pump you will get it done for free and not have to pay the 100 bucks
 

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About fuel pumps- how often do you guys change your fuel filter? I'm running an experiment myself about how long a fuel pump will last if you change your fuel filter regularly as recommended.

As far as the other recommendations- great job guys. I can't really add anything.

Clean the MAF
Check the spark plugs for correct gap and deposits.

Well, one thing I might add- how about trying some STP gas treatment to see if it is bad fuel.
 

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Unless it is a big coincidence, something connected with what you just did caused the problem. And I doubt it has anything to do with the oil.

That leaves the air filter operation. Perhaps something was dislodged when you removed the filter.....something affected the MAFS. I'd start there first.
 

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Clean your MAF sensor and reset the ECU.... that usually takes care of all kinds of small issues with the Focus.
 

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Sounds similar to when my DD had a dirty MAF....
 

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Discussion Starter #12
Here's an update guys. Checked the oil. It seemed just slightly overfilled, so I drained a tad out so it was no longer overfilled. I took out the MAF sensor and it looked clean as could be. Just to be safe I blew some compressed air through it to clean out any dust and reset the ECU.
Same rough idling. I re-checked the air filter and the entire CAI for any problems and couldn't find any.
I figured it had to be something with the fuel system. So, I went to the store to buy some fuel system cleaner and on the way my car stalled while stopped at a red light. [mecry] I put the stuff in and filled up at the gas station I always use to fill up my car. Came home, problem seems to be gone. [woot]

My mom was the last one to fill up my car and I know she did not fill up where I normally do, so I'm guessing, and hoping, it was just a really really bad tank of gas. I've had bad tanks before, but nothing like this. Hopefully everything is fixed for good now.

Thanks for all the help and suggestions guys!
 
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