Intermittent rough idle

2004 Taurus SEL - Duratec engine. Last week it was warm outside so I took the garden hose out and cleaned all of the salt from the bottom of the car, the suspension and the wheel wells. I thought everything was fine but then when I went to start it the engine was running very rough, so I let it warm up to evaporate any water that might have gotten on it. Now it runs great EXCEPT for when I'm at a red light. It will be idling fine but then every so often, out of the blue, it gets a rough jolt and then it's idling fine again. The first time it happened I actually thought someone had hit the car from behind (that's how noticable it is). It lasts for a second and happens approximately every 30-40 seconds. When the light turns green and I start to go it seems to run fine. I'm guessing water got some place where it shouldn't have, but it should have all evaporated away by now. I looked for a disconnected vacuum line but didn't notice anything. Looking at the engine everything looks fine.

How should I trace this problem down, or what should I check? :confused:

"when I went to start it the engine was running very rough, . ." Obviously you sprayed something electrical to make it run rough.

Clean the MAFS and make sure the PVC valve is good and the gromet it sits in is tight. Have you taken it on the highway and run it 60 MPH or more for 15 minutes? That should dry up or suck or blow out any moisture left. Park it in the dark and crank it up and let it idle, open the hood and see if you see or hear a spark jumping. If it does that to long it will probably set a CEL code but for now that's all I can come up with. OH! Might not be relative, but take the negative battery terminal loose for several minutes then hook it up and drive it around. That clears the computer and it has to relearn your driving habits and how to idle.

Sounds like you may have gotten some water down one or more of the spark plug wells. These are supposed to be sealed, but if you happened to be able to force some water down one, it may have a hard time evaporating out.

MAF sensor, as Huney1 suggested, would be another item to check. An intermittant problem with that could cause exactly the symptom you describe. Check the connector for moisture.

If neither of those pan out, then check other electrical connections for moisture and vacuum lines for having been pressure washed off. How aggressive of a spray did you use with the garden hose?

-Rod

Clean the MAFS and make sure the PVC valve is good and the gromet it sits in is tight.
Will look at the MAFS first thing tomorrow, but the car does not have a PVC valve. I will take it off and spray it with electrical cleaner.

Have you taken it on the highway and run it 60 MPH or more for 15 minutes?
Yes, several times.

take the negative battery terminal loose for several minutes then hook it up and drive it around. That clears the computer and it has to relearn your driving habits and how to idle.
Yes I was thinking about doing this, but I was told that it has to stay off for at least an hour.

How aggressive of a spray did you use with the garden hose?
It wasn't very strong. Similar to what comes out of a showerhead.

I was told take the terminal loose when the engine is hot, leave it loose all night then connect it in the morning when the engine is cold. Also heard take it loose two minutes. Try it both ways, cant hurt anything.

As Rod suggested, you have water somewhere it is having difficulty evaporating away. If you can get the plug wires off easy take a thin cloth and small, flat screw driver and push the cloth down beside the plug so it will suck up any water. If you can get it close enough to the plug holes a hair dryer should dry out the moisture. How about squirting electrical cleaner in the plug holes to dry up the moisture and spray some up inside the plug wire where it connects to the plug. :dunno: WD40 = Water Displacement but I'd be real careful because it is HIGHLY FLAMMABLE.

Well I thought I just cleaned the MAFS, but now I noticed that there is another sensor right next to it that actually says "MAFS". The only confusing part is that I always thought that the MAFS was an electrical part, and this one is set up to a vacuum line. So now I'm trying to find out what a MAFS actually looks like for my car :(

Here is a picture that explains it better.

http://www.imnotinvisible.com/pics/MAFS.jpg

You cleaned the correct part. The "MAFS" lettering in the intake air tube is just to designate which end that hose connects to. One end to the MAFS and one to the throttle body. Those letters are strictly for orientation purposes.

-Rod

I believe you have the same "hot wire" MAFS and it is electrical. Essentially the little wires get hot and the amount of air passing over them cools them and that gives the computer a reading on how much air is flowing through the intake and then it meters the fuel accordingly. Best explaination I have at the moment. Here, read it for yourself: http://en.wikipedia.org/wiki/Mass_flow_sensor CRC has a new product out especially for cleaning MAFS. http://www.crcindustries.com/hd/content/prod_detail_print.aspx?PN=05110

CRC has a new product out especially for cleaning MAFS.
That's the same company that makes the electrical cleaner that I use to clean the MAFS sensor. I will definitely be picking some of this new stuff up though. Any stores carrying it yet?

After I cleaned the MAFS sensor the car runs INCREDIBLE now, and it actually ran good before this too, but never as good as it's running now. It idles sooo smooth that sometimes it's hard to tell that the car is running, and with that Mobil1 synthetic trany fluid (that I put in a few months ago) it shifts so smoothly that you can't even tell where one gear ends - and the other gear starts. It's like melted butter :p But all is not perfect. The gas milage is now around half as much (from 22-25 to around 11 mpg). This engine is by far the best engine that I've EVER seen from any car company (although some Honda engines are pretty good too) :bigthumb: I would have thought however that with it running so incredibly well that the gas milage would be better, but it doesn't appear so :(

Other than that, the car runs like a raped ape, and on the freeway when the passing gear kicks in you'd think you were in a GT40 :p Even when I baby it the best milage I get is only around 13 :(

"Even when I baby it the best mileage I get is only around 13 :frown:"
That's not very good mileage, my 03 Vulcan gets around 20 and I don't baby it. Try this: When the engine is hot and you park it for the night take the negative terminal loose and leave it off all night, then hook it up in the morning. Start it up and let it idle for about 15 minutes then hop in and drive it around town and on the highway at 60 mph a few miles and the computer re-learns how you drive. Something about taking the terminal loose while the engine is hot then connecting it when the engine is cold. I did that with mine and all I can tell you is it worked.

I can't hold a candle for Rod or Way2Old, but something is wierd because it would have to be running real rich and seems to me it would throw a CEL code indicating it is running rich. If I stick my finger in the exaust pipe and wipe inside the pipe it comes out clean, try that with yours and see if it comes out black.

Check out this thread: http://www.automotiveforums.com/vbulletin/showthread.php?t=673872

Inside the exhaust is a little black, but I thought that all exhaust is black :sly: I called AutoZone and they said that they don't carry that new MAFS cleaner, so I'll look on the internet tonight for it. I did take the battery terminal off for a few hours, but the engine was cold so I don't know if that will effect it, I would think it shouldn't, but I have to go on the freeway this Tuesday so Monday night I'll get the engine warm and take the battery terminal off all night to see if that changes anything. If we idle the engine for 15 minutes I would think that would hurt the milage even more, since the car is not moving. Or do you mean warm it, then reset the milage guage, and then take it on the freeway?

I found the CRC MAF sensor cleaner at Advance Auto Parts locally (Iowa).

If your coolant temperature sensor is out of spec, it could cause the engine to run rich, yet still seem to be running smoothly. As Huney1 suggested though, I would expect to get a code for a rich bank or two if it were running THAT rich. Are you sure the fuel tank was filled completely and the trip odometer was reset correctly when for the tank you recently calculated fuel economy on?

Do you have access to a scan tool with the datastream mode that you can monitor the oxygen sensor real time readings with?

-Rod

See the third reply from the top. We delved into it pretty good and will save me a lot of typing. http://www.automotiveforums.com/vbulletin/showthread.php?t=673872

"Or do you mean warm it, then reset the milage guage, and then take it on the freeway?" Forget the mileage gauge. Crank it and let it idle 15 minutes then drive it as you normally would. Note I used old Electrical Parts cleaner and it did a fine job cleaning the MAFS wires. That CRC stuff is new and 'prolly hasn't hit all the parts stores yet, I checked Advance here near Savannah, GA and they don't have it yet. Going to Charleston tomorow so I'll swing by Pep Boys and see if they have it.

Oil jumped to $62.00 a barrel today because they captured those British sailors, so best get it tuned up to get the best mileage you can because gas is slowly going through the roof. It's $2.42 here now highest it's ever been.

OH! This is good. The global warming folks are saying NASCAR racing puts a lot of unnecessary emissions into the atmosphere. HeHeHeHe . . . I'd like to see one of them stand in front of ole Bubba wearing his Richard Petty NASCAR cap and tell him that.:popcorn:Break out the pop corn and watch Bubba do his thing . . . . :iceslolan

I can hardly wait to buy that cleaner. I found some at Amazon (http://www.amazon.com/CRC-Mass-Flow-Sensor-Cleaner/dp/B000EGH57G) but I will call NAPA tomorrow before I order it. According to the label (http://www.crcindustries.com/faxdocs/label/lb05110.pdf) it definitely controls MPG - so I have nothing to lose and everything to gain by trying it out. Read some of the reviews at Amazon, they are very favorable. I will also check to see if we have a Advance Auto Parts around. A new part sells for 130.00, which I think is a little high from what I've seen of the part (a few thermister type resistors) but none the less I will clean it first. We do not have access to a scan tool.

We bought the MAFS cleaner tonight from Advance Auto Parts (thanks for the tip shorod :)) We warmed up the engine and when we got home we disconnected the negative battery cable. We cleaned the MAFS and reinstalled. Car will sit all night and in the morning we will re-connect the battery cable and let it idle for 15 minutes. Then we'll take it on the freeway and drive it around town. I think that's all we need to do. We'll let you know if the MPG gets any better... :)

WOW! All I can say is that MAFS cleaner is simply amazing! :grinyes:

It looks like we're now getting 24-26 in the city, and a amazing 30-33 on the highway :eek: Of course for doing something like MPG it takes time to get an accurate reading, but initial reports indicate that at the very least our milage has doubled :) I guess I'm so surprised because we used CRC contact cleaner on the MAFS just a week or so ago, so I didn't really think is was all that dirty, but after using the MAFS cleaner it did look visually cleaner. This now confirms it. My guess is that the contact cleaner may have left a residue of some kind behind, where as the MAFS cleaner does not. All I know is that there is a noticable difference. Before, when you were at a red light the tach needle used to fluctuate a little, which I always thought was normal. But now it is ROCK steady! :)

I want to thank everyone in this thread for all of their help with this. I love taking care of this car. I'm not one to try to save money on anything that it needs. I only care about it running as good as possible and now it does. I whole heartedly recommend that everyone give this MAFS cleaner a try. You've got nothing to lose, and everything to gain. At around 7.00 a can it will easily pay for itself in short time :grinyes: