Mercury wont idle

60

Asked by May 20, 2015 at 07:00 PM about the 2004 Mercury Grand Marquis LS Ultimate

Question type: Maintenance & Repair

I have a 04 grand marquis 4.6l and it wont idle. It gave me a the codes for bank 1 and 2 is too lean. So I looked around unplugged mass air flow sensor ran better. So I bought a new one and plugged it in and does the same thing. Runs good unplugged but with a rough idle. With it plugged in it stalls on idle. I'm mechanically inclined so what do i test? I dont see nor hear any vaccum leaks. What do I test where do I start?

7 Answers

67,295

If you've ruled out a vacuum leak, check the fuel pressure. It may be low due to a clogged fuel filter, failing fuel pump, or failing fuel pressure regulator. Check the upstream oxygen sensors as well. The downstream oxygen sensors are not involved since they do not control air/fuel mixture adjustments. -HTH. -Jim

Best Answer
1,245

Interesting! I had the same problem, ran well with MAF disconnected. I new one fixed it, but I had replaced the upstream O2 sensors prior, even though they didn't give codes except lean. I'd replace them, just because. How many miles on the car?

1,245

If those things don't work, think about the TPS. (throttle position sensor) They are mechanical, and can wear out.

60

Yea looked at tps and o2 sensor prices will be replacing praying not ecu. Car only has 120k. Havnt replace any mechanical stuff. Only had since 97k. Only thing ive done to it is put p71 H pipe with 3 inch exits at rear. Ran great with those. I did put little over 500 miles on it that day when problem hit. Trying to find way to test vacuums and im borrowing 10k car tester today should tell me. Ill update this tonight. Car will be adding another 500-600 miles hopfully.... this weekend

60

Ended up being crack in vacuum line on throttle body

1,245

Thanks for letting me know. Those vacuum leaks will "get you"

67,295

Yes, thank you for letting us know. Very glad you got it fixed and that it was an inexpensive, relatively easy fix too. -Jim

Your Answer

Add photo

Related Questions

  • Mercury wont idle 7 answers

    I have a 04 grand marquis 4.6l and it wont idle. It gave me a the codes for bank 1 and 2 is too lean. So I looked around unplugged mass air flow sensor ran better. So I bought a new one and plugged it...

    2004 Mercury Grand Marquis LS Ultimate

    -

    Maintenance & Repair

  • Idle speed on my 1987 Mercury Grand Marquis is going up and down - what' s wrong ? 3 answers

    When my Mercury is running for a while at idle speed, engine speed suddenly starts going up and down. Sometimes the engine even turns off after a few seconds. I checked all vacuum hoses - they seem to...

    1987 Mercury Grand Marquis

    -

    Maintenance & Repair

  • 2002 mercury grand marquis turned off while i was driving and wont turn back on whats wrong 1 answer

    I put in a new fuel pump bought a alternator checked the battery it sounds like its going to start but wont turn over I don't know if its the starter or the fuel injectors in the engine or something e...

    2002 Mercury Grand Marquis LS Premium

    -

    Maintenance & Repair

  • 99 Mercury Grand Marquis 2 answers

    So I've had a a 99 Mercury Marquis sitting in my garage for about 2 years, I've been trying to get it to run lately. So I've changed the fuel pump, cleaned out the tank and put it back on and I got...

    1999 Mercury Grand Marquis 4 Dr LS Sedan

    -

    Maintenance & Repair

  • 1999 mercury grand marquis 1 answer

    I have a miss in my engine at idle more profound driving on rd like a bad plug wire i changed plugs coil pack fuel filter cleaned out throttle body other stuff car is using more gas now because of...

    1999 Mercury Grand Marquis 4 Dr LS Sedan

    -

    Maintenance & Repair

Grand Marquis

Looking for a Used Grand Marquis in your area?

CarGurus has 1,835 nationwide Grand Marquis listings starting at $2,000.

ZIP:

Search Mercury Grand Marquis Questions

Mercury Grand Marquis Experts

#1 Tracy Hooks
Tracy Hooks
Reputation 5,520
#2 kbro
kbro
Reputation 2,080
#3 Js08016
Js08016
Reputation 1,790
View All

Related Models For Sale

Used Ford Crown Victoria
16 Great Deals out of 1,221 listings starting at $1,595
Used Lincoln Town Car
36 Great Deals out of 1,791 listings starting at $1,500
Used Chevrolet Impala
592 Great Deals out of 34,064 listings starting at $899
Used Ford F-150
2,059 Great Deals out of 207,350 listings starting at $1,499
Used Mercury Marauder
22 listings starting at $9,300
Used Chrysler 300
404 Great Deals out of 19,200 listings starting at $850
Used Honda Accord
947 Great Deals out of 77,741 listings starting at $899
Used Ford Taurus
270 Great Deals out of 20,574 listings starting at $1,995
Used Cadillac DeVille
4 Great Deals out of 1,627 listings starting at $1,988
Used Buick LeSabre
19 Great Deals out of 1,919 listings starting at $1,000
Used Chevrolet Tahoe
557 Great Deals out of 31,373 listings starting at $1,500
Used Ford Mustang
537 Great Deals out of 45,845 listings starting at $1,999

Used Cars For Sale

2011 Mercury Grand Marquis For Sale
33 listings starting at $4,495
2010 Mercury Grand Marquis For Sale
88 listings starting at $3,150
2009 Mercury Grand Marquis For Sale
6 Great Deals out of 83 listings starting at $3,599
2008 Mercury Grand Marquis For Sale
11 Great Deals out of 138 listings starting at $2,250
2007 Mercury Grand Marquis For Sale
8 Great Deals out of 132 listings starting at $2,495

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.