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Rough idle on cold starts

Tiny
MGOBLUE78
  • MEMBER
  • 2000 MERCURY MARQUIS
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 134,000 MILES
Once engine warms up seems to run fine. I’ve replaced IAC, spark plugs (coppers), fuel filter, and O2 sensors. I will sometimes get lean codes from both banks. I’ve looked for vacuum leaks and even cleaned the mass air flow sensor. Any ideas?
Monday, March 11th, 2019 AT 4:19 PM

17 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good evening,

What are all the codes?

A common issue for this is the intake manifold leaking down into the valley.

Let's start with the codes.

Roy
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Monday, March 11th, 2019 AT 4:23 PM
Tiny
MGOBLUE78
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  • 12 POSTS
Hi Roy, I’ve gotten a p0174 and p0171 codes.
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Monday, March 11th, 2019 AT 4:57 PM
Tiny
ASEMASTER6371
  • MECHANIC
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Got it.

These codes indicate a lean condition and is usually a vacuum leak at the intake manifold.

Will you be doing this job yourself? It is a big job.

Roy
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Monday, March 11th, 2019 AT 5:06 PM
Tiny
MGOBLUE78
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Yes, I will be doing the work.
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Monday, March 11th, 2019 AT 5:10 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Procedure

Change Vehicle Bookmarks Library Request Conversion Calculator Technician's Reference - Collision

intake manifold
108
Community 25 Create Quote
2000 Mercury Grand Marquis V8-4.6L VIN W
Procedures
Vehicle Engine, Cooling and Exhaust Engine Intake Manifold Service and Repair Procedures
PROCEDURES
Removal
1. Disconnect the battery ground cable.
2. Drain the engine cooling system.
3. Remove the air cleaner outlet tube.
4. Disconnect the fuel line.
5. Remove the wiper arm and pivot shaft.
6. Remove the drive belt.
7. Raise the vehicle on a hoist.

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8. Disconnect the electrical connector at the Crankshaft Position (CKP) sensor.
- Disconnect the pin-type retainer from the A/C compressor bracket.

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9. Disconnect the electrical connector from the A/C compressor.

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10. Remove the oil bypass filter.

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11. Disconnect the oil pressure sensor electrical connector and the Power Steering Pressure (PSP) switch electrical connector.

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12. Disconnect the Exhaust Gas Recirculation (EGR) tube from the exhaust manifold.
13. Lower the vehicle.

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14. Disconnect the two differential pressure feedback EGR hoses.

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15. Disconnect the RH heated oxygen sensor electrical connector.

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16. Disconnect the fuel charging wiring electrical connectors from the eight ignition coils.

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17. Disconnect the fuel charging wiring electrical connectors from the eight fuel injectors.

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18. Disconnect the accelerator cable and the speed control actuator cable.

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19. Remove the cables from the EGR tube heat shield and position out of the way.

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20. Remove the bolts and the EGR tube heat shield.

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21. Disconnect the Evaporative Emissions (EVAP) return tube, the main chassis vacuum supply line, and the EGR valve vacuum supply.

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22. Disconnect the Positive Crankcase Ventilation (PCV) tube assembly at two locations and remove.

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23. Disconnect the electrical connector from the EGR vacuum regulator solenoid.

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24. Disconnect the vacuum line from the EVAP canister purge valve.

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25. Disconnect the generator cable and electrical connector.

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26. Remove the bolts and the generator mounting bracket.

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27. Remove the upper radiator hose.

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28. Disconnect the electrical connector from the Idle Air Control (IAC) valve and the Throttle Position (TP) sensor.

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29. Disconnect the heater water hose.

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30. Disconnect the EGR tube from the EGR valve.

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31. Note: The LH heated oxygen sensor and the transmission electrical connectors are attached to the wiring bracket and must be separated from the bracket.

Remove the wiring bracket.
- Disconnect the wiring connectors.
- Separate the transmission harness from the stud.
- Remove the nut and the bolt and remove the bracket.

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32. Remove the bolts and the throttle body.

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33. Separate the fuel charging wiring pin-type retainer from the crash bracket.

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34. Remove the bolt and the stud and remove the crash bracket.

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35. Disconnect the vacuum lines and remove the vacuum harness.

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36. Remove the studs and the fuel injection supply manifold and fuel injectors as an assembly.

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37. Remove the bolts and the ignition coils.

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38. Remove the bolts and the water outlet adapter.

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39. Remove the water thermostat.

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40. Remove the bolts and the intake manifold.
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Monday, March 11th, 2019 AT 5:22 PM
Tiny
MGOBLUE78
  • MEMBER
  • 12 POSTS
Thank you for the help! Not sure how soon this project will happen but I’ll be in touch with any help needed. Thanks again for your time and help!
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Monday, March 11th, 2019 AT 5:35 PM
Tiny
ASEMASTER6371
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You're welcome.

Always glad to help.

Roy
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Monday, March 11th, 2019 AT 5:42 PM
Tiny
MGOBLUE78
  • MEMBER
  • 12 POSTS
Hey Roy, just a little update. I had to take my car to a mechanic to diagnose the problem. He did a smoke test and couldn’t find a vacuum leak or anything else wrong other than cleaning my maf sensor. That did seem to help but only for a day or so. He noticed I had Autolite spark plugs to which I was told there pretty much junk. I replaced them with motorcrafts and also replaced the maf sensor. Since then I haven’t had a check engine light. I still have a rough idle on cold starts. My short term fuel trim is high 20-30%(at idle) until engine warms up then drop’s to around 0% like it should be. Any ideas or do you still feel it’s my intake?
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Saturday, April 27th, 2019 AT 9:49 AM
Tiny
ASEMASTER6371
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I need the long term trim readings, not the short.

Did they do a compression test?

It sounds like a carbon issue on the intake valves.

Roy
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Saturday, April 27th, 2019 AT 9:55 AM
Tiny
MGOBLUE78
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I don’t think he did. Long term fuel trim is 15-25% at idle. Drops down as you give it gas.
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Saturday, April 27th, 2019 AT 10:07 AM
Tiny
ASEMASTER6371
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Running lean.

Did you check the fuel pressure?

Roy
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Saturday, April 27th, 2019 AT 10:16 AM
Tiny
MGOBLUE78
  • MEMBER
  • 12 POSTS
Not yet, but will now.
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Saturday, April 27th, 2019 AT 10:23 AM
Tiny
ASEMASTER6371
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Sounds good.

Keep me updated.

Roy
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Saturday, April 27th, 2019 AT 10:56 AM
Tiny
MGOBLUE78
  • MEMBER
  • 12 POSTS
Hey Roy, sorry for such a long delay. I finally checked my fuel pressure. First, I did car off, turned ignition to run, reading - 6psi. Then I started the car and let it idle for a few minutes, reading - 32psi. Turned car off, let it sit for fifteen minutes, reading - 30psi. I’ve also noticed since the outside temperatures are warmer now, on cold starts my long term fuel trim starts at 15% or less then will drop as low as 5% when car gets up to normal temperature.
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Saturday, June 22nd, 2019 AT 9:12 AM
Tiny
ASEMASTER6371
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Got it.

You need a fuel pump. The pressure is way low.

Roy

REMOVAL
1. Remove the fuel tank. For additional information, refer to Fuel Tank. See: Fuel Tank > Procedures
2. Disconnect the pressure transducer connector on the top rear comer of the fuel tank.
3. Clean the area around the fuel pump mounting flange.

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4. Remove the bolts and remove the fuel pump.

CAUTION: The fuel pump must be handled carefully to avoid damage to the float arm and the filter.

5. Remove and discard the fuel pump mounting gasket.
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Saturday, June 22nd, 2019 AT 11:12 AM
Tiny
MGOBLUE78
  • MEMBER
  • 12 POSTS
That’s what I was afraid of. Thank you for all your help!
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Saturday, June 22nd, 2019 AT 4:12 PM
Tiny
ASEMASTER6371
  • MECHANIC
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You are welcome.

Always glad to help.

Roy
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Saturday, June 22nd, 2019 AT 4:14 PM

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