Revs high when started then chugs

Tiny
JSAUDE
  • MEMBER
  • 2000 MERCURY COUGAR
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 159,000 MILES
When I start the car it revs to about 3 grand then drops to almost nothing (below a grand) and starts chugging really bad. When driving u can feel it missing and when u come to a stop sign it chugs and jerks worse. Today I started it and both the rpm and speedometer gauges both buried as soon as it started and did not come down. I only have issues when it is cold out and the colder it is the worse the car gets. I was told it was the mass air flow sensor so replaced it and did not change anything if anything, its worse now. Can someone please help? Thanks n advance.
Wednesday, December 11th, 2013 AT 8:29 PM

5 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
If I understand, the problem deals with the engine idle speed. Have you checked for vacuum leaks? Have you checked the idle air control valve (IAC)? The IAC is responsible for maintaining the engine idle speed.
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Thursday, December 12th, 2013 AT 5:20 AM
Tiny
BMDOUBLE
  • MECHANIC
  • 1,139 POSTS
Sounds exactly like vacuum leaks. Inspect all of the hoses on top of the engine, more than likely you will have some split or collapsed hoses there. Make sure to retrieve any engine codes, you can also pour some water where the upper and lower intake bolt together to ake sure the gasket is good, if it's bad you will see a change in the idle and possibly hear a gurgling noise.
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Friday, December 13th, 2013 AT 11:52 AM
Tiny
JSAUDE
  • MEMBER
  • 3 POSTS
Ok now I started it and it revved really high and the tachometer and speedometer both buried and soon as it started. What would cause this?
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Friday, December 13th, 2013 AT 2:12 PM
Tiny
JSAUDE
  • MEMBER
  • 3 POSTS
Had vehicle ran for codes and its showing both O2 sensors one is showing lean and one is showing rich. Also showing misfire on cylinder 3. The battery was dead and terminals all corroded. Could the "build up" be the catalytic converter?
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Sunday, December 15th, 2013 AT 2:47 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
The corrosion on the battery has nothing to do with the converter. The misfire on #3 could cause a problem for the sensors. Have you checked to see if you can determine what the misfire is caused from?
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Sunday, December 15th, 2013 AT 4:57 PM

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