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Old 12-20-2009, 19:04   #1 (permalink)
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'99 Taurus - runs rough when cold

Hope people can give some suggestions... I've got a 1999 Taurus 3.0 with an OHV engine. It has a high/inconsistent idle when cold. The idle bounces between 900-1300 rpms and the gas milage is crud. Before it warms up, when I put it into gear the engine dies. After just a few minutes warming, it's fine.

I've changed the plugs and wires, gave it a new air filter and fuel filter. Ran a bottle of injector cleaner through it, too. (it was past time for all these). I tested the Engine Coolant Sensor, but it seemed fine (~40K resistance cold, and ~10K when warm). Unfortunately, I had a problem getting the plug back on and damaged the sensor, so I replace it. I've poked around for vacuum leaks but haven't found anything.

The only lead I have is the idle air control valve. I measured the DC voltage at about 5 volts. The Haynes book says it should read 10.5-12.5 volts. Is this low voltage significant? What might cause it? If I understand corectly, this is the signal going TO the idle air control valve, so I haven't diagnosed the valve itself. Am I thinking straight about that? Or is there some sort of feedback from the valve? I'm not sure where to go from here.

Any thoughts on why it dies when I put it into gear?

Thanks!
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Old 12-20-2009, 19:16   #2 (permalink)
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Re: '99 Taurus - runs rough when cold

Have you messed with the idle screw on the throttle body? If so, you'll have to go through the entire "minimum idle adjustment" procedure. Otherwise, start by cleaning the throttle body. Then remove the idle air control valve and shoot throttle body cleaner into the bypass passage, making sure none of the solvent gets into the solenoid.

Then disconnect the battery cables for about 15 mins and reconnect. Idle air control valve voltage should be 9.9-12.5 volts. The lower the voltage, the bigger the vacuum problem in the engine. #1 problem is carbon buildup in the intake, followed by dirty injectors and carbon buildup on the valves.

That's why you should start with the throttle body cleaning and valve cleaning.
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Old 12-20-2009, 19:27   #3 (permalink)
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Re: '99 Taurus - runs rough when cold

Lower voltage indicates an idle problem such as, carbon build up in the intake, dirty injectors and build up on the back of the intake valves. The
lower the voltage, the larger the problem. A sticking BPA solenoid will also cause unusual BPA voltages.
If the voltage is under 9.50 volts, the solenoid is working too hard and minimum idle is low because of adjustment or dirty throttle bore. Voltage near battery voltage indicates the solenoid is off too much. This is usually caused by vacuum leaks. It might also help to clean the MAF with the special MAF cleaner. Do you have any codes present? Autzone will check them for free.
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Old 12-20-2009, 19:39   #4 (permalink)
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Re: '99 Taurus - runs rough when cold

No engine codes. I haven't messed with the idle screw, either. I'm a little hesitant to get into the throttle body though, because I've never played with one before. Sounds like cleaning it is a good start. Dumb questions, but what is the "bypass passage?" And how do I go about cleaning the throttle body?

Thanks for the thoughts.
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Old 12-20-2009, 19:48   #5 (permalink)
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Re: '99 Taurus - runs rough when cold

I should have said IAC voltage. Some manufactures call it that, You were checking the voltage I mentioned. Cleaning the throttle body is fairly easy. Take the hose off, open the throttle and clean the area inside. You can also take the IAC valve off and clean it too. Don't forget the MAF.
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Old 12-22-2009, 12:35   #6 (permalink)
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Re: '99 Taurus - runs rough when cold

Thanks for the ideas. I pulled the MAF off and ran a bunch of cleaner through it (bought the special MAF cleaner, though the parts-jockey said I could use throttle body cleaner). I also cleaned the throttle body with its own cleaner. I wanted to take the throttle body off, but couldn't get a new gasket in time, so I just did it in place. The car was at a slight angle, so all the cleaner ran back out. Looked pretty brown coming out. I sprayed about 2/3 of a bottle through it, which seemed less brown when I was done. Unfortunately, this didn't help... still runs rough when cold and stalls when I go into gear. If the engine is at all warm, it runs fine. I also noticed that if I rev the engine in park, it tops out at about 4000 rpms; at about 3800, it starts running rough, like its misfiring.

At this point I'm out of time and my wife is out of patience, so I'm taking it to my local mechanic.

Again, thanks for the help!
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