ENGINE IDLE ROUGH P0171 P0174

2000 Ford Taurus

Tiny

jmruperto

February, 12, 2012 AT 3:26 PM

Taurus Idle Problem:

2000 Ford Taurus SEL, V6, 3.0L (182 CID); DOHC, automatic, 125,000mi.

When engine is ‘COLD’ (morning startup and afternoon startup), engine starts immediately then comes to normal idle speed. Within a few seconds engine begins to idle roughly even while idle speed is constant. About one half of the time, the condition is not sever enough to cause stalling, so I can get the car in gear and drive until the engine warms up enough for the problem to go away. The engine runs like the day I bought it when it is hot. The other half of the time, after the engine begins to idle roughly, the RPMs drop and the engine stalls. After several restarts, and running the engine speed up to 2000 RPM for a minute or two I have been able to prevent the stalling and drive until warm-up. When the engine is idling roughly it is enough to shake the car, sometimes it make what I call a loping sound but the RPMs are constant.

About a month ago I bought an OBD II tester and have consistently gotten a DTCs P0171 System Too Lean (Bank 1), and DTC P0174 System Too Lean (Bank 2), and I have also gotten engine misfire codes, (somewhat inconsistently), everything from P0300 (random misfire) to misfire on specific cylinders.

So far I have: (1) changed the gas filter, (2) changed the spark plugs, (3) change all of the ignition coils where I have gotten a misfire DTC for a specific cylinder (three total), (3) replaced the upper intake manifold gaskets (since I had to remove this to get to the spark plugs), (4) changed the EGR gasket (since I had to remove this to get to the spark plugs), (4) checked for obvious vacuum leaks (visually and by touch), (5) tested both key-on and engine-on fuel injector rail pressure, (6) listened for fuel injector valve clicking, and (6) tested the PCV valve by applying a vacuum to the connecting hose.

Changing the fuel filter and spark plugs gave the engine more power (that I had not noticed was lost) but it did not correct the problem. Changing the coil for the first DTC code (P0306) that I received, eliminated an annoying little misfire that I would notice when the engine was hot and at idle, but it did not correct the cold engine problem. Changing the other 3 coils did nothing. I was never able to find any obvious vacuum leaks, all of the injectors seemed to be clicking (so I assume none are sticking) and the fuel pressure test was within spec. Finally, while the PCV valve did move in response to applied vacuum, however it is 12 years old and did not have the crisp clicking noise as it snapped back into place, but it did move freely and go back into position. Why did Ford make this valve so hard to get to on my engine?

I can send one of the diagnostic reports from Innova if I can figure out how to do this.

Help would be appreciated.

I love this site : -) it has helped me many times

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8 Answers

Tiny

Jacobandnickolas

February, 12, 2012 AT 5:54 PM

The two things that need to be focused on are vacuum leaks and the IAC.

Tiny

jmruperto

February, 12, 2012 AT 6:16 PM

Can you be more specific? I failed to mention this in my initial question but I did several other tests. Regarding the IAC, I pulled the connector with the engine running, both when it was running smoothly and when it was acting up (running rough). In each case the engine either stalled or the idle became rougher.

Can you provide specific test procedures?

Also, why is when the engine is hot (been running for 10 minutes or so) it idles smooth at silk? I would assume if vacuum is an issue it would be an issue whether the engine is hot or cold.

Tiny

jmruperto

February, 12, 2012 AT 6:25 PM

Can you tell me if I am showing up as an "Upgraded Question" customer? I have tried twice to donate through Paypal, but it does not seem to be working. It completely bombed the first time(something with Paypale site)and the second time it seemed to work but I have received no confirmation. My Paypal account is showing no activity. Is there a way to check this?

Tiny

justdon

February, 18, 2012 AT 4:49 AM

I experienced a cold start roughness and found it to be the upper intake needed re-torqued. A vaccuum leak was there until the engine warmed up and expanded the metal, which sealed the leak until it cooled again.

Tiny

jmruperto

February, 18, 2012 AT 2:42 PM

Justdon, really good point about the expansion and subsequent sealing due to material expansion.

I purchased a 0-250in-lb torque wrench to reinstall the upper intake manafold when I replaced the spark plugs, and also replaced the seals before the reinstall. I realize this could still be an issue if I didn't get the bolts installed properly even though the torque may be correct.

Also it is possible that the manafold is cracked (mine is plastic) or that the lower manafold is leaking. I am going to try a test I read about, i.E. Using carburator cleaner to spray near the manafold and other vacuum lines to check for leaks. If the engine accelerates then the cleaner is getin in due to a leak. The safer route to this test is to use pressurized smoke generator, but these machines are $1300 and I can't afford one.

Thanks for the suggestion.

Tiny

justdon

February, 19, 2012 AT 5:02 AM

Ahhh. Good old plastic. Hope it didn't warp on you. Just curious, are you loosing any coolant? If so, maybe a quick pressure test and a check for combustion gasses in coolant may be warranted to eliminate intake or head gasket trouble.

As for the smoke machine. That's number one on my wish list.

Tiny

justdon

February, 19, 2012 AT 5:06 AM

Carb. Cleaner is a good way to detect vacuum leaks. I use starting fluid. (Just a preference)

Tiny

Djpiper2126

August, 10, 2013 AT 4:54 PM

You should change the lower intake gaskets as well. It has been known in this car for the lower intake gaskets to become smashed and lose its seal until the engine is warm and the gaskets expand

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