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

56,575

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
1,110

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?

1,110

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

1,110

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

56,575

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

  • Grand Marquis 2004 wont start 8 answers

    Hi. My mercury Marquis is making issues and it doesnt start. I am having this issue from last few weeks. Funny thing is that its start when it wants to. Initialy i thought that issue is with battery...

    2004 Mercury Grand Marquis GS

    -

    Maintenance & Repair

  • cant keep 1998 mercury marquis running, it'll start and run if i Feather the pedal, once released stalls out. 3 answers

    1999 Mercury Grand Marquis 4 Dr GS Sedan

    -

    Maintenance & Repair

  • Very high idle 5 answers

    Cleaned engine. Blew off, dried everything, disconnected all wiring connectors blew dry and reconnected all wiring, hoses, and removed all coilplugs blew out dried boots and applied dielectric lu...

    2002 Mercury Grand Marquis

    -

    Maintenance & Repair

  • AC / Heat / Idle Issues 1989 Mercury Grand Marquis 1 answer

    OLD PROBLEM: I had a suspected vacuum leak in my Grand Marquis as when I accelerate the AC would cut out. Idling is a little uneven and sometimes will accelerate faster than it should. I found a vac...

    1989 Mercury Grand Marquis GS

    -

    Maintenance & Repair

  • 99 mercury cougar wont start? 2 answers

    Replaced, camshaft positioning sensor, spark plugs and wires, coil pack, starter, alternator, fuel pump, fuel filter, and the pressure regulator. After sitting for a while it will crank, ...

    Mercury

    -

    Maintenance & Repair

Grand Marquis

Looking for a Used Grand Marquis in your area?

CarGurus has 2,238 nationwide Grand Marquis listings starting at $1,500.

ZIP:

Search Mercury Grand Marquis Questions

Mercury Grand Marquis Experts

#1 Tracy Hooks
Tracy Hooks
Reputation 4,900
#2 kbro
kbro
Reputation 1,970
#3 Js08016
Js08016
Reputation 1,490
View All

Related Models For Sale

Used Ford Crown Victoria
6 Great Deals out of 1,501 listings starting at $2,900
Used Lincoln Town Car
39 Great Deals out of 2,160 listings starting at $1,700
Used Chevrolet Impala
918 Great Deals out of 36,377 listings starting at $1,800
Used Chevrolet Tahoe
1,061 Great Deals out of 32,236 listings starting at $1,495
Used Ford F-150
3,370 Great Deals out of 203,970 listings starting at $1,273
Used Ford Mustang
722 Great Deals out of 38,312 listings starting at $1,750
Used Chrysler 300
519 Great Deals out of 20,717 listings starting at $1,500
Used Ford Taurus
350 Great Deals out of 22,303 listings starting at $1,499
Used Chevrolet Silverado 1500
2,596 Great Deals out of 149,096 listings starting at $1,800
Used Cadillac DeVille
1,974 listings starting at $1,600
Used Buick LeSabre
7 Great Deals out of 2,349 listings starting at $1,768

Used Cars For Sale

2011 Mercury Grand Marquis For Sale
3 Great Deals out of 41 listings starting at $7,617
2010 Mercury Grand Marquis For Sale
100 listings starting at $2,999
2009 Mercury Grand Marquis For Sale
5 Great Deals out of 115 listings starting at $3,495
2008 Mercury Grand Marquis For Sale
8 Great Deals out of 175 listings starting at $2,900
2007 Mercury Grand Marquis For Sale
11 Great Deals out of 172 listings starting at $1,500