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#4128542 - 11/23/21 11:41 AM 2001 - Low Idle leading to P0305 - Need idle fixed
SYRPanther Offline
Stranger

Registered: 11/22/21
Posts: 3
Loc: Syracuse, NY, USA
2001 Mercury Grand Marquis. 125K miles.

There's two issues here. The one I need to solve is the low idle in gear when warm. If I can keep it idling above 570ish hot, in gear, It won't set a p0305. I'll take care of the possibly low compression in the spring.

When warmed up (after a highway drive, even sitting in traffic), it wants to idle at 500 RPM. This has been causing a cylinder 5 misfire. I do believe that cylinder is a bit weak and won't fire well at that low of an RPM. If I do a clear flood and crank over, every 8th cylinder sounds odd so it's not a flat spot on the flexplate's ring gear. I would assume it's a weak cylinder? But that only manifests when it's around 500 RPM. The car likes to idle at 900 or so in neutral when hot.

I've squirted around with starting fluid, some propane and have not found any vacuum leaks. At idle (900-1000 RPM) in neutral, it's pulling 18.5 in/hg of vacuum. That's well within spec. Idling in gear, it's 13.5 in/hg at 500 RPM which seems normal. I'll try to smoke it this weekend in case I missed something.

I cleaned the IACV (and did the relearn) and that seems to have made the issue worse. Now if I stop hard (instead of coasting where it will figure itself out), it will drop down to 400 RPM for a second. Same happens when I put it in gear warm.

Tested the voltage on the TPS and it appears to be working 100% , the readout on my basic scanner also agrees with it working right.

There is no pinging / hesitation during moderate throttle acceleration with torque converter locked at low RPM. If I get on it too much it kicks down. But no pinging / hesitation during low RPM acceleration , and no pinging / hesitation at part throttle cruise leads me to believe EGR and DFPE are fine.

I believe the IACV to be bad. If I'm in traffic or a drive thru where it wants to idle low and rough, if I two foot it and lightly blip the gas pedal a few times, it will eventually compensate and adjust and idles at 570-600 smoothly and won't set the misfire code. And it will work until I take off from the stoplight / drive thru and come to a stop again.

Someone else tried a very basic way to figure this out before. It still had all 8 original coils but the plug in cylinder 5 was an autolite, the other 7 were original motorcraft. I also cleaned the MAF when I got the car as maintenance. It's something I do with CRC cleaner on my 2001 F350 with the 5.4 regularly.

So ...

  • 8 new motorcraft plugs and coils - wasn't troubleshooting anything, just maintenance.
  • Idles at 500 RPM, drops to 400 sometimes
  • Cylinder 5 misfire
  • Can't find any major vacuum leaks with starting fluid or propane
  • If I tap the gas a few times idling in gear it'll figure itself out and idle normally
  • Eliminated TPS as problem
  • No pinging / hesitation ; don't believe EGR or DFPE
  • Cleaning and relearning the IACV made it worse
  • Adjusting idle screw and relearning didn't do anything
  • Cleaned MAF with CRC MAFS cleaner


Obviously if I replace the IACV it's only going to be with a Motorcraft one. Not interested in aftermarket junk electronics.

If NY didn't require no CEL to pass inspection I wouldn't care.

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#4128552 - 11/23/21 12:40 PM Re: 2001 - Low Idle leading to P0305 - Need idle fixed [Re: SYRPanther]
RF_Overlord Offline

Poobah

Registered: 12/14/02
Posts: 7769
Loc: MA
Originally Posted By SYRPanther
If NY didn't require no CEL to pass inspection I wouldn't care.

This doesn't directly address your issue, but may be relevant:

Check your NYS DMV regulations. In MA, which pretty much adheres to the same set of regs as NY, any vehicle 15 years or older is exempt from the emissions portion of the state inspection. As long as all the safety items pass, they don't care if the CEL is on. I was told this by a state inspector and verified it myself with the RMV.
_________________________
'03 Mercury Marauder (The Blackbird)
Trilogy Motorsports supercharged #61
Too many mods to list / Driveway Queen

'04 Grand Marquis LS Limited Edition (Spruce Green)
Daily Driver (Thanks, Adam!)

'00 Grand Marquis GS (Silver)
Rotted frame and broken transmission crossmember
Being resurrected...slowly.

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#4128556 - 11/23/21 01:37 PM Re: 2001 - Low Idle leading to P0305 - Need idle fixed [Re: SYRPanther]
SYRPanther Offline
Stranger

Registered: 11/22/21
Posts: 3
Loc: Syracuse, NY, USA
NY is 25 years old or GVWR above 8500 pounds.

If it's a 1996-2000 it'll pass with 2 open monitors. If this was a 2000, I could just clear the misfire code and it would pass with open misfire monitor and catalyst. Unfortunately this can only have one open.

I have two other vehicles - one is a 2001 F-350 so it's emissions exempt due to weight. The 2000 Jeep Cherokee always has evap codes, but I can reset and just keep the tank 100% full so it won't run the monitor then get it inspected.

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#4128562 - 11/23/21 02:25 PM Re: 2001 - Low Idle leading to P0305 - Need idle fixed [Re: SYRPanther]
RF_Overlord Offline

Poobah

Registered: 12/14/02
Posts: 7769
Loc: MA
25 years? Damn.

Sounds like you've done your emissions research already. Maybe my input will help someone else in future.
_________________________
'03 Mercury Marauder (The Blackbird)
Trilogy Motorsports supercharged #61
Too many mods to list / Driveway Queen

'04 Grand Marquis LS Limited Edition (Spruce Green)
Daily Driver (Thanks, Adam!)

'00 Grand Marquis GS (Silver)
Rotted frame and broken transmission crossmember
Being resurrected...slowly.

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#4128564 - 11/23/21 02:32 PM Re: 2001 - Low Idle leading to P0305 - Need idle fixed [Re: SYRPanther]
RF_Overlord Offline

Poobah

Registered: 12/14/02
Posts: 7769
Loc: MA
Only other thought I had was to try swapping the injector for cylinder 5 with another cylinder and see if the misfire code tracks.
_________________________
'03 Mercury Marauder (The Blackbird)
Trilogy Motorsports supercharged #61
Too many mods to list / Driveway Queen

'04 Grand Marquis LS Limited Edition (Spruce Green)
Daily Driver (Thanks, Adam!)

'00 Grand Marquis GS (Silver)
Rotted frame and broken transmission crossmember
Being resurrected...slowly.

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#4128730 - 11/25/21 12:10 PM Re: 2001 - Low Idle leading to P0305 - Need idle fixed [Re: RF_Overlord]
White Falcon LS Offline


Posting Addict

Registered: 01/01/02
Posts: 19128
Loc: SoCal
Originally Posted By RF_Overlord
Only other thought I had was to try swapping the injector for cylinder 5 with another cylinder and see if the misfire code tracks.


Exactly what I was thinking; swap the injector and the ignition coil around. Also inspect the connector to make sure it isn't broken, and it sits right on both the coil and the injector. This is pretty common. In the past, I've had to zip tie them on until I was able to get a new connector.
_________________________
Lucifer: '01 Grand Marquis GS Convenience
Tuned By Marty @ Mo's Speed Shop

In Memory of Ned Nuss, Rick Richardson and Matt (2vmodular)

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