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Hello all,

I've posted a few times on here about my Frankenstein 2006 Taurus with the 3.0 Vulcan. I bought the car with low miles and had to invest a ton of time and money into it to make it my daily driver. Now I'm just starting to nit-pick an ongoing issue. Some of the work done has been replacing the heads due to both being cracked, replaced thermostat, all plugs (twice), all plug wires (twice), coil pack (4 times), fuel injectors, IAC, Thottle Pos Sensor, PCV, PS pump, rack and pinion, starter, PCM, catalytic converters, and a few other small parts. Like I said, lots of money but I did majority of the work myself (what I could actually do without needing large equipment). I call it the Frankenstein car because although the CarFax had a clean title for it when I bought it, the front end has been partial replaced because the fenders are 24V DOHC fenders (has the this OEM stickers on them), there is paint over-spray on the headlight wires and other parts of the front end of the car, and the engine bay fuse box is cracked in half. Throughout all the work done to this over the past 13 months by me, I still have an outstanding issue with it... it idles high and doesn't always let off the gas when driving.

For example, when I start the car, RPM spikes to around 1700-1900, holds very briefly, drops to 1300 for 10-20 seconds, then to 1100 for another 10-20 seconds and then settles just over 1000 until put into gear. Once placed into gear, it drops to around 800-850. Intermittently while driving, I'll let off the throttle and the car will hold speed OR accelerate for another 2 -3 seconds and then let off. Biggest problems with this is that A) could cause and accident, and B) wears my brakes more because of having to use them more. I've checked for vacuum leaks and haven't found any. Used carb cleaner and stethoscope methods. I also had a smoke test done on the vehicle and they said the fuel cap and vapor canister were leaking. Replaced the fuel cap but haven't touched the vapor canister. I've replaced the IAC, the Throttle Positioning sensor, and cleaned the Mass Air Flow Sensor (with MAFS cleaner). I use Motorcraft Parts for this car so everything is OEM, to include the computer that was replaced and programmed by the local Ford Dealership. Additionally, when the climate control is turned on, the idle is constantly jumping from 900 RPM to 1300 RPM. The only time it doesn't jump is if I turn the blower onto feet only and then it idles smooth. I understand that with more load turned on then the engine will work harder but that seems a little excessive to me. I could be wrong though.

I'm curious if it's a wire issue, fuel supply issue or if it's there's something else I can look at for verifying what could be wrong with it. I have the old and new IAC that I swapped to verify there was no change with how it acted. There are codes popping for this, only a P0430 (which annoys me because I've already had a shop replace the cats earlier this year). I think the idle issue could be causing the cat to go bad again but I could be wrong. I drive on average 120 miles per day (55-60 miles each way) of which is 95% interstate driving bouncing between 65 mph and 75 mph. Average fuel economy is around 23 mpg to 26 mpg, depending on the outside temp and the traffic. If anyone has any advice or recommendation, please feel free to voice it. Like I said, I'm getting to the point that I'm done investing but even with all the money I've thrown into it, it's became a pretty reliable little car. I got it around 70k miles, it now has almost 110k miles (yes roughly 40k in a year). Thus the reason I am trying to get it to run a little better. Thank you all for your time and assistance/advice.
 

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Checking for vac leaks by listening or with carb cleaner usually doesnt work well. It doesnt take much of a vac leak to cause issues.

What are the long term fuel trims on each bank at warm idle and with the engine under load, such as at 50 MPH cruise? High positive LTFTs at idle that drop toward lower numbers with engine under load the accepted way to determine if you have a vac leak.

A smoke test is also a good way to look for vac leaks.

Assuming the new cat wasnt some cheapo piece of crap, a slow switching pre cat O2 sensor or contaminated pre cat O2 sensor with a chemical shift can generate 420/430 codes.
 
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Sounds like bad IAC valve. Try putting one of the ones you replaced just for a test. I installed a aftermarket IAC that performed just like your description. I know the valve is OEM but I would try a swap.

But also sounds like a vacuum leak in the HVAC lines to the dampers
Manual Schematic.png
 

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Discussion Starter #4
Checking for vac leaks by listening or with carb cleaner usually doesnt work well. It doesnt take much of a vac leak to cause issues.

What are the long term fuel trims on each bank at warm idle and with the engine under load, such as at 50 MPH cruise? High positive LTFTs at idle that drop toward lower numbers with engine under load the accepted way to determine if you have a vac leak.

A smoke test is also a good way to look for vac leaks.

Assuming the new cat wasnt some cheapo piece of crap, a slow switching pre cat O2 sensor or contaminated pre cat O2 sensor with a chemical shift can generate 420/430 codes.
Jeff, thanks for the input. I will pull the LTFTs tonight on my way home and see if I can get proper data for you. I did a smoke test but only flagged a bad fuel cap and a bad vapor canister. As for the Cat, I'm not positive what the local shop threw into it but I'll make some calls and find out. I remember them saying though that he was going to try and reuse the original O2 sensors if he could so it could very well be one of those. Again, thanks for the input and I'll get that data for you tonight.
 

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Discussion Starter #5
Sounds like bad IAC valve. Try putting one of the ones you replaced just for a test. I installed a aftermarket IAC that performed just like your description. I know the valve is OEM but I would try a swap.

But also sounds like a vacuum leak in the HVAC lines to the dampers View attachment 215568
Automender, you have helped me countless times already on these forums so I'll always take your advice. Is there more information to that image I can get as far as what all the numbers are? When I get home tonight, I'll check the maintenance book I have at the house (Haynes I believe) and see if it has any more information. Since the original one and the new OEM IAC are doing the same thing, do you recommend me having the new one get warrantied replaced for a new one and try that or pick up an aftermarket one to see what it does differently? Trying to keep things simple and not shotgun parts. Thank you again for your time and assistance.
 

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Discussion Starter #6
All, here are screen shots from my OBD II readings on my way home today. I have hot start-up, cruising at 55 mph, and post trip idle. Looks like O2 sensor number 2 on bank 2 (cyl 4-6) isn't responding (not sure if that's normal or not), and it looks like bank 2 is running rich. Please correct me if I'm incorrect. If you need more data, please let me know. I'm looking for any recommendations moving forward please.

Hot Start Idle.jpg
215570
215571
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215575
 

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Automender, you have helped me countless times already on these forums so I'll always take your advice. Is there more information to that image I can get as far as what all the numbers are? When I get home tonight, I'll check the maintenance book I have at the house (Haynes I believe) and see if it has any more information. Since the original one and the new OEM IAC are doing the same thing, do you recommend me having the new one get warrantied replaced for a new one and try that or pick up an aftermarket one to see what it does differently? Trying to keep things simple and not shotgun parts. Thank you again for your time and assistance.
I would never get a aftermarket IAC valve and I guess I believe the OEM is ok but since it is only to bolts I would test swap with one you took off. How are the mounting o rings on the IAC?

The diagram I found on the internet and no more info was they only good diagram of the dampers and how it works. I looked quick to see if they was a hose only that functioned when damper to floor was eliminated Looks like line 5 or 2 going to actuator 24 could cause a vacuum leak when floor vents are not selected. Have you pulled out the climate control recently because there is a group of hoses that goes to the selector switch you could check. But also the AC is used on all other damper position except heat. Which brings me back to IAC valve. Short term fuel trims at idle will indicate a vacuum leak if they are above 5% in my opinion. If they drop significantly at higher RPMs that it is a good sign of a leak. I think yours looks good but not 100% sure. One other possibility is your compressor is starting to go bad and put excessive load, more than what the computer expects.
 
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