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Problems with '99 Taurus idle speed

07-13-2007, 03:02 PM
i have a 1999 ford taurus sedan that lately is driving me crazy...

i just fixed a leak in the radiator tubes so i dont know if that affects what im talking about now

when i bring the car to a complete stop then let go of the breaks... the car goes a lot faster at idle speed than normal, as a matter of fact the speed increases. i checked on it with a computer to see what the problem was and it said it was the idle air control valve, which i already ordered and will be putting it on tomorrow...

anyone know if that really might be the problem? or might something else be causing it too... its driving me insane.

as a matter of fact... i've had to put the car in neutral several times to make it slow down because the breaks get way too heavy... and its shut off a couple times when i've put it back on drive...

any suggestions please?

07-13-2007, 05:07 PM
Since the increase/decrease in RPM's is so profound believe you're on the right track with the Idle Air Control valve. If yours has a mass air flow sensor clean it and new PCV valve and new grommet runs five or six bucks. Do a search for cleaning MAFS and do not touch the wires with anything because they are britle and cost $130.

07-14-2007, 12:15 AM
Idle air control valves are a known problem on these vehicles. You can try cleaning the old one with carb cleaner. Also clean all the orifices from the IAC valve into the throttle body. Clean the throttle plate too. Just make sure you don't get carb cleaner into the electrical portions of the IAC.

07-14-2007, 04:45 AM
Good info on how the IAC works.
Check Idle Control Valve (IAC) Motor Operation
The purpose of the Idle Control Valve (IAC) valve assembly is to control engine idle speed, while preventing stalls due to changes in engine load. The IAC valve, mounted in the throttle body, controls bypass air around the throttle valve.
By moving a conical valve known as a pintle, "IN" toward the seat (to decrease air flow) or "OUT" away from the seat (to increase air flow), a controlled amount of air moves around the throttle plate. If engine speed is too low, more air is bypassed around the throttle valve to increase RPM. If engine speed is too high, less air is bypassed around the throttle valve to decrease RPM. The PCM moves the IAC valve in small steps called counts which can he measured using a scan tool connected to the Data Link Connector (DLC).
During idle, the proper position of the IAC valve is calculated by the Powertrain Control Module (PCM) based on battery voltage, coolant temperature, engine load, and engine RPM. If the RPM drops below specification and the throttle valve is closed, the PCM senses a near stall condition and calculates a new valve position to prevent stalling.
If the IAC valve is disconnected and reconnected while the engine is running, the resulting idle RPM may be wrong and resetting of the IAC valve will be required.
The IAC valve will reset when the ignition is turned "ON" then "OFF." When servicing the IAC valve, it should only be disconnected or connected with the ignition "OFF."
If the PCM is without battery power for any reason, the programmed position of the IAC valve pintle is lost, and replaced with a default value. This causes the engine idle to be unstable for a period of approximately seven to 30 minutes.
The IAC valve affects only the idle characteristics of the vehicle. If it is fully retracted, too much air will be allowed into the manifold and idle speed will be high. If it is stuck closed, too little air will be allowed in the manifold, and idle speed will be too low. If it is stuck part way open, the idle may be rough, and will not respond to engine load changes.
IAC Valve (Typical)

Remove IAC Valve.
Inspect IAC Valve operation.
Connect the positive (+) lead from the battery to terminal +B and negative (-) lead to terminal Na, and check that the valve is closed.
If operation is not as specified, replace the IAC valve.

Connect the positive (+) lead from the battery to terminal +B and negative (-) lead to terminal Nb, and check that the valve is open.
If operation is not as specified, replace the IAC valve.

As always, check the service manual for the proper procedures and specifications for your particular vehicle.

07-14-2007, 04:53 AM
"Idle air control valves are a known problem on these vehicles."
Mine started loping again yesterday now doing it with the AC on or off, varying maybe 50 to 100 RPM's but nowhere near shutting off at idle. Thought I'd take it off and use some MAFS cleaner on it 'cause I can see how the piston sticking wouldn't be a good thing. Anyway, anything special to replacing it, adjustments, etc? Or alll I do is take the old off and put the new on, plug it up and I'm good to go? Advance has them for 50 bucks. Thanks and nice to have another PRO technician with us. :)

Guess you're aware of this new product from CRC: I found it at Advance.

EDIT: 5/16 socket and took me 15 minutes to take it off and clean it. I sprayed the holes with CRC MAFS cleaner and let it soak and took Q tips and went down in cleaning and it was real cruddy inside. Took six Q tips to get it clean inside. Let it dry then took a couple drops of spray lube and put on the shaft and around piston. Tried to crank it but no go at all. Let it sit a couple minutes then it cranked right up. Letting it idle in the driveway and warm up then I'll horse it around a mile or two and see how she idles. Seemed to lope the most when it was real hot in the afternoon, so we'll see how it does now. Thanks for the tip, I hope you saved me fifty buckaroos.

07-14-2007, 09:37 AM
well i just bought an idle air control valve, a brand new one and i replaced it with the old one and the car accelerates just like before... driving me insane...

07-14-2007, 09:56 AM
I can understand your frustration. OK, I have a few minutes before we leave for the beach house. It can be vacuum leak/air leak, IACV, bad PCV valve or grommet to loose lets air around it. Hoses and tubes all tight and no cracks in the rubber from the filter to the aluminum plenum.
Since you replaced the IAC that's ruled out. Down inside the two holes in the plenum was real nasty like black grease so I washed it out the the MAFS cleaner. How about the throttle body plate, you can see it and is it moving freely and not stcking?

Some forum discussions on your problem:
Question:2003 Ford Taurus 3.0 V6_mileage: 48000. Several months ago our Taurus city gas mileage dropped from about 23 mpg to 16 mpg. The highway miles are still close to 27 mpg. I have had it at two dealers who say no codes show. They replaced the IAC and fuel pump, with same results. When started even in warm weather the car jumps to over 2,000 rpm and remains for up to one minute. Seems to idle rough at about 800 rpm bouncing + or - 100 rpms. At stop lights it wants to idle high sometimes. Is this some type of vacuum leak? Thanks.
Answer: Test the fuel pressure regulator to see if it is leaking raw fuel into the engine. If that checks out okay, your problem is probably caused by a faulty MAS (mass airflow sensor).

Google "99 ford taurus rough idle" and you'll get a lot of hits and best I can tell you is read through them and do research and sooner or later you should hit on something.

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