2003 Mercury Sable buck from stop unless let off gas or sto

Tiny
ELADDRALLIM@YAHOO.COM
  • MEMBER
  • 2003 MERCURY SABLE
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 218,000 MILES
The car idles good. Starts good, hot or cold. Runs smoothly. Never dies.

But, when car is cold, it will buck and jerk like crazy when starting up normally from a stop sign or light. If you let off gas or stomp on it, the problem stops.

Lately, though, problem has happened a couple of times when warm. Coming off interstate to stop, then when start forward car bucks or acts like it is flooded. Let off gas or stomp on it and it seems to get better. Once past initial bucking, car runs and accelerates fine.

Please tell me it's not the transmission!
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Saturday, March 14th, 2009 AT 4:21 PM

5 Replies

Tiny
JAMES W.
  • MEMBER
Firstly, do you get a check engine light? If yes, I'll need to know what codes are stored in ECM memory. Then, spark plugs can cause this. When was your last tune up? Please advise.
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Saturday, March 14th, 2009 AT 7:43 PM
Tiny
ELADDRALLIM@YAHOO.COM
  • MEMBER
No check lights come on. This has been a problem for a while, but getting worse. About 6 months ago I had the engine tuned and spark plugs replaced hoping it would take care of the problem. It didn't. Except for the occasional bucking, this car is in great shape and runs well. If I sit in park and "race" the engine, I don't get any blue or grey smoke. Most miles are commute interstate miles. Very little stop and go.
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Sunday, March 15th, 2009 AT 10:13 AM
Tiny
JAMES W.
  • MEMBER
I re-read your post and what I see is; The "bucking" you described sounds like what is called a "lean cough". This is when your cruising down the road, top down, radio playing and your computer is doing just what it's supposed to do. It leans out the air/fuel mixture for optimum economy. But, you need to change lanes so you accelerate just a little bit and "poof" the engine coughs. If I am correct so far, the cause is; the ECM can't richen up the mixture fast enough to compensate for the added air allowed by the throttle. Two sensors can cause this condition. 1- throttle position sensor TPS). If you do a lot of highway driving, it will have a tendancy to wear a "weak" spot in the sensor's coil 'cause that's where you hold the throttle 80% of the time.
2- The O2 sensor. The signal from this may be holding the fuel/air mixture a little "too" lean for the ECM to compensate for light acceleration. Each of these sensors could be defective but, still be in range enough to not trigger the check engine light. My first suspect would be the TPS. Hope this helps.
Note; Both these sensors can be tested with a volt/ohm meter or a hand held diagnostic unit.
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Sunday, March 15th, 2009 AT 12:26 PM
Tiny
ELADDRALLIM@YAHOO.COM
  • MEMBER
Thanks!

I will check this out and try to follow up.
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Sunday, March 15th, 2009 AT 8:15 PM
Tiny
JAMES W.
  • MEMBER
Complete
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Saturday, March 21st, 2009 AT 8:26 PM

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