Post Reply 
 
Thread Rating:
  • 0 Votes - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Mercury idels rough- check engine light on
03-25-2013, 10:56 PM
Post: #1
Mercury idels rough- check engine light on
I have a 1997 Mercury Mystique with a 2.0 - 4cyl. auto trans and about 121k miles. Started ideling rough, wanted to die at stops, check engine light came on after about a week. Had codes read. P 0171 came up. Websight suggested cleaning Mass Air Flow Sensor.
Carefully removed MAF sensor, cleaned with MAF spray and reinstalled. CEL went off and idel returned to normal...for two days. Now light is back on and idel is low and rough again. Any ideas that won't cost me a bunch of money that I don't have will be appreciated. Thanks.
Find all posts by this user
Quote this message in a reply
03-26-2013, 12:09 AM
Post: #2
RE: Mercury idels rough- check engine light on
I would suggest cleaning the IAC (Idle Air Control) which is that small by-pass port by the throttle plate. You can probably use the same cleaner you already have. Once you get that done see if you can get the codes cleared out of the ECM so next time everything is a fresh start. If that same code returns you may need to continue your search for vac leaks and other common causes of rough idle.

BTW, it would help to know if the idle is just rough or if it's also wandering from the normal speed. If the car does not have a tach you may need someone to use a full function scanner to get more info.
Find all posts by this user
Quote this message in a reply
03-26-2013, 01:35 PM
Post: #3
RE: Mercury idels rough- check engine light on
(03-26-2013 12:09 AM)Rupe Wrote:  I would suggest cleaning the IAC (Idle Air Control) which is that small by-pass port by the throttle plate. You can probably use the same cleaner you already have. Once you get that done see if you can get the codes cleared out of the ECM so next time everything is a fresh start. If that same code returns you may need to continue your search for vac leaks and other common causes of rough idle.

BTW, it would help to know if the idle is just rough or if it's also wandering from the normal speed. If the car does not have a tach you may need someone to use a full function scanner to get more info.

Car has a tach. "Normal idle is around 900. When it's acting up idle drops to 400 or 500, sometimes lower when it wants to die.
Find all posts by this user
Quote this message in a reply
03-26-2013, 10:05 PM
Post: #4
RE: Mercury idels rough- check engine light on
Ok, that's helpful. I'd still do as I posted previously and see if it improves. Reason being is the code you see is sometimes a symptom rather than the exact fix. For example, if the check engine light came on for high coolant temp you probably wouldn't jump to clean / replace the sensor. You'd more likely let it cool off and see what's up with the rest of the cooling system first. Same goes for a misfire / stalling situation code. Believe it or not I have seen a code for "multiple cyl misfire" due to a bad fuel pump AND (you won't believe this one) running out of fuel!

What I am driving at is that sometimes experience in the field still points me to cover the simple items before spending time & money.

Back to your specific situation.... clean the IAC, inspect the vac lines and air intake boot, then see if the same code comes back.

BTW, a bad (read: sticking) IAC usually will NOT set any codes but can cause intermittent stalling so don't be shy, clean it 2 or 3 times, which it might need if it's never been done. Just blast some of your fluid into the side bore by the throttle and let it soak for a minute then start the car. Repeat if necessary.
Find all posts by this user
Quote this message in a reply
12-02-2015, 09:33 PM
Post: #5
RE: Mercury idels rough- check engine light on
Yea my recommendation is look for vac leaks and check exhaust for leaks. All so check gas cap randomly sometimes that can be the cause of the crap.
Find all posts by this user
Quote this message in a reply
Post Reply 


Forum Jump:


User(s) browsing this thread: 1 Guest(s)