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Old 09-01-2011, 13:32   #1 (permalink)
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2005 Ford Taurus - Surging

I have scavenged the forum and have seen many people discuss issues with their Taurus's similar to mine but none of them are resolving the issue.

Details:
Mileage - 150,xxx
Transmission - Rebuilt Jasper w/100k Warranty
TPS - Replaced twice
MAFS - Unplugged and driven but the issue still remains

Description of Issue:
When I am driving (typically after the car has been warmed up) at a steady speed my car will down-shift as if I have tapped the gas pedal and rev up momentarily and then return to normal. Sometimes it will do it just once when it has an 'episode' other times it will do it 5+ times before it 'calms down'.

-MAFS Trial-
With the MAFS Sensor plugged in, when the car has an 'episode' it will down-shift and rev up to 3k+ and take its time getting back into the proper gear.

With the MAFS Sensor unplugged, the car has an 'episode' and it just basically jerks real quick and then it goes right back into gear.
--
I am only guessing but I think the MAFS manages the smoothness of the shifting by knowing the amount of air coming in so it will communicate with the rest of the system so to create less shift shock, among other purposes that the MAFS has. When the MAFS is unplugged it (as stated above) it will grab straight on to the gear (almost feels clutchless at points) and doesn't piddle around shifting gears.

There are a few other thoughts I've had based on posts on this and other forums and I would like to see what anyone thinks about them and/or if they have other ideas.

--Idea #1--
Speed Sensor. I am unfamiliar with the layout of the Taurus as far as where and how many speed sensors there are. From my understanding, when you are using cruise control that it will utilize the speed sensor(s) to detect whether or not the car needs to speed up or slow down to maintain the set cruise speed. I almost thought this could be a next plan of action however the issue happens both with and without cruise control on. So it could be a speed sensor but I don't think (guessing) the speed sensors would play that sort of factor if the issue is occuring without running cruise control.

--Idea #2--
EGR Valve. I've looked at some things but it pretty much states that the car would do more stalling than surging if there was an EGR issue but I figured I could take a look and see if there were loose connections and/or if it was cheap enough to just replace to verify its a working part.

--Idea #3--
Could still be the TPS. As stated i've replaced the original TPS and then replaced the TPS that I replaced the original with. However I am a little concerned that maybe the 'cheapest' TPS is not my best option especially with the summer heat being at its highest (going down now) right now and when the car is hot it seems to be worse. I'm thinking that the cheaper option may be throwing readings off after it is heated up (creating gaps between sensors, electrical contacts, etc. ? within the unit).

Thanks for any input you have. I am upside down on this car as it is and I'm hoping to keep it in a fairly good condition especially with a Jasper Rebuilt Tranny that is warranted past 200k on the spedo. Hoping to get rid of it within the next year but I want it to be in the best condition so as to minimize the amount of cost to me for trading it in.
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Old 09-02-2011, 08:18   #2 (permalink)
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Re: 2005 Ford Taurus - Surging

Also a note, I had the plugs and wires replaced < 200 mi ago and just changed the oil last night to see if that does anything. I've also ran a bottle of STP Fuel Injector/Carb Cleaner through the tank to clean things up a bit.

-Oil Change Schedule-
Usually through the most of the year i'll run about 5k between oil changes because I do 100% highway miles and it (1) gets expensive having the oil changed every 4-5 weeks if it did it at 3k [starting to do this myself so doing it more frequently won't cost so much $$] (2) it seems crazy to change practically clean oil. However with the mileage of the car now getting up there the oil is starting to look dirtier when I change it and with the weather being at its hottest (heat = poorer oil function) I'm thinking more frequent oil changes during the hot season would be best.

I will post again if the oil change resolved the issue.
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Old 09-02-2011, 09:56   #3 (permalink)
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Re: 2005 Ford Taurus - Surging

WOW!! this is a brain teaser. Let us do some more research into this...I will forward this to a few of our guys that are more knowledgeable.
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Old 09-06-2011, 08:26   #4 (permalink)
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Re: 2005 Ford Taurus - Surging

Latest Update -

I changed the oil but it did nothing, except what changing the oil normally does. Kind of glad (that it wasn't as stupid as not changing the oil like I should) but I would have liked to have the issue resolved at that point. A bit of a two edged sword.

I decided to go ahead and prove my insanity and replace the TPS sensor yet again, from a different brand and parts store altogether. So far it is working fine however the temperature has dropped considerably from where it was at (was 95-100 now its 70-80).

I also looked into some information on the IAC Valve due to its connectivity directly to the TPS. I took it off and it looked like the ports could use a little bit of cleaning, regardless of whether or not this is the cause of my issues. It'll cost $65'ish to get a new part so i'm more keen to clean as opposed to replace yet. Plus, everything i've read says everything to do with idle and pulling off from a stop but nothing about cruising at steady speeds. Figured its worth a shot. I hope for warmer weather to drive my car in to see how it acts with the hotter weather but the cooler weather makes it nicer for washing the car, house, doing yardwork, etc... all that married man stuff haha.

Thanks again, will update when something changes!

~Kale
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Old 09-06-2011, 19:12   #5 (permalink)
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Re: 2005 Ford Taurus - Surging

Have you had the codes read? Autozone will check for free. That may help in the diagnosis.
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Old 09-14-2011, 08:39   #6 (permalink)
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Re: 2005 Ford Taurus - Surging

I've had the codes read when the Check Engine light was on, but that only turned on during the MAFS testing I was doing and, as would be expected from messing with the MAFS, it said 'too much oxygen in the exhaust'. This was the only code reported. Can't remember the # off hand but that was the verbose of it. Since then however I let the check engine light stay on, just for kicks, and after a couple of days the light went out on its own. Doing pretty good as far as not having the check engine light on with 150k miles on it. My other Ford/Mercury Sable/Taurus' all had persistent check engine lights for O2 sensors.

--Update--

Last week I was on vacation and so I only went to work twice (woohoo!) but those two days were cooler than the weather had been in a while here (last week it was around mid 70s, where it had been high 90's or low 100's).

During the cold spell my car seemed to be working just fine. There were a few times where the car seemed to act up but nothing near what it was doing in the scorching temps. This week however, the temperatures jumped back up for Monday and Tuesday and my car showed its true colors once again.

The new (3rd) TPS Sensor did not resolve the issue so now I am deciding that it is a waste of my time to try the TPS again.

I'll look further into the IAC Valve and do some cleaning as suggested on some other sites and forums. The symptoms of a faulty/dirty IAC Valve do not parallel with the issues i've been having but as I stated previously it looks like it could use some cleaning, and it's better to remove all doubt than to know there was something else I could've tried. I'm out of ideas at this point and so doing something that may do nothing feels more productive than not trying anything.
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Old 09-14-2011, 18:14   #7 (permalink)
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Re: 2005 Ford Taurus - Surging

It could also be a temp sensor. It'd be great to be able to monitor the data on the system.
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