I have owned this DOHC Taurus for about three weeks. I bought it from an Estate sale. No warranty. No history. No former owner for that matter. I have driven it about 650 miles.
At first it ran very roughly, and at high idle. Scan codes indicated a miss on #3, and multiple misfires on first 1000 RPM on start-up. It doesn’t seem to be using any coolant, so I DO NOT suspect a bad head gasket or cracked head. I changed all six plugs and checked the resistance of the plug wires. Plug #3 was definitely bad. The intake manifold gaskets were replaced at that time. It still has the high idle, 2000 to 2500 RPM. I need to put it in neutral when coming to a stop, if I want to stop easily. Sometimes, the idle will slow to 1000 RPM at which time it will run roughly. Stepping on the gas brings it back up to 2000+ where it stays until its mood changes again.
I have looked for other vacuum leaks, pulled and pushed on hoses, shot carb cleaner around the new manifold gaskets, and swapped out the Idle Air Control with an unknown (hopefully good) one borrowed from my favorite friendly salvage yard.
Here are some questions Should an IAC be open with no current fed to it? I can see light coming through to the other side of my unit as well as the borrowed one. With 12V applied to the electro-magnet, how far should the plunger move? I think it should move towards more open. ??
No experience w/the IAC operation on the Taurus, but if the problem isn’t that, other things to consider
PCV valve malfunction or air leak somewhere in that system
Brake booster air leak
MAP air leak (if so configured)
Intake manifold gasket air leak
Have you tried spraying starter spray here and there, see if the engine speeds up? I had a high idle speed on my Corolla one time, trying to remember what caused it … hmm … oh, yeah, it was a faulty IAC combined with a faulty thermostat that was sticking partially open and wasn’t allowing the engine to heat up to normal operating temperature.
Edit: Your buying a Taurus at an estate sell reminds me of a funny story. I was trying to sell an early 90’s Taurus at an estate sale; I test drove it, and it worked fine, heater worked, AC worked, all the lights worked, even though it had been sitting for several months unused. So I put in in the driveway with a for sale sign on it. A couple comes by with 4 kids. While I’m discussing the cars merits and demerits of the car with the couple I didn’t notice all 4 of their kids were in the car and flipping all the switches on the dashboard … lol … Somehow the kids got it configured so the headlights wouldn’t turn on. And I couldn’t figure out how to reverse what they had done. The bottom line, I sold it to the couple at a discount b/c the head lights wouldn’t turn on.
Tapping on the IAC when the engine is fully warm did not change the RPM.
Removing the plug from the IAC made no difference either.
I cut an IAC plug in off of a junk Ford, and used it to feed 12 volts directly into the IAC. The engine revved from 1900 to 2800 RPM. I also see that I have 13.6 volts at the plug removed from the IAC. When I replaced the plug onto the IAC, it went back to the 1900 RPM I’d been experiencing.
I took the air cleaner plenum and MAF off of the car and cleaned the MAF with the recommended cleaner made by CRC. No change. I also cleaned the throttle butterfly area, along with two the small holes in the butterfly itself. I don’t think the holes were dirty. There was some gum at the bottom of the butterfly.
Pumping the brakes as a test of the vacuum booster and its hose made no difference.
I don’t think there is a PCV per se. There is a hose connecting the cam cover to the area of the 3" ringed hose at the throttle body. The hose and its end fittings appear to be OK. There is vacuum where it should be, and moving the hose makes no difference.
Another thing to check is the coolant temp sensor for the computer.
If this sensor is telling the computer that the engine coolant is at -30 degrees, the computer will cause the engine to go to fast idle, and stay there.
I’m assuming this car uses a conventional cable system to transfer the accel pedal movement to the throttle valve. If so, check the cable linkages, maybe the cable is sticking inside the sheath. Are you able to see the throttle valve when you take the air cleaner stuff off? Does it appear to be almost fully closed? It doesn’t take much of an opening at that spot to increase the engine rpm quite a bit. If in doubt, you may have some gunk built up on the other side of the throttle valve from the PCV and EGR systems. Not an uncommon thing. I had a little bit of that problem on my Corolla a couple years ago and had to remove the throttle body to be able to get at the throttle valve from the back side and give it a thorough cleaning. On the Corolla it isn’t much of a job to remove the throttle body, maybe 15 minutes. If its equally easy on your Taurus, and nothing else seems to be working, give that a try.
I have cleaned the throttle butterfly area. There is no gunk there. There was only a small amount anyway. The cable linkage moves freely.
Would the coolant temp sensor show up on my cheap scanner? If it’s the same sensor for the gauge, it always is about half way up once warm. Is the same sensor used for both the gauge and the computer.
our cruise control linkage stuck on once. it had the throttle held wide open. you could disconnect the throttle cable and verify that the butterfly is closed. and than hook it up. if it remains closed and idle is very high than the IAC may be involved?
If you think the problem might be the IAC, is there a way you can just eliminate it from the equation completely ? As a test I mean. That’s how I figured out the IAC on my Corolla wasn’t working, I completely blocked it off so functionally it wasn’t there at all. This caused the engine rpm to be too low on cold starts, but I solved that just by keeping my foot on the gas pedal enough to keep it going until the engine warmed up enough to idle on it own, about 2 minutes.
After all those tests, I took the plunge and bought a new IAC yesterday for $52. Well, that was not the problem. It behaves exactly the same with the new one as it did with the old.
Question: Are both wires at the plug going into the IAC supposed to be hot at one time or another, or is one just a ground? Only one of mine is hot at the plug, or when punctured just short of it. Hot or cold engine makes no difference.
From what I can determine, the ecm controls the IAC using digital pulses, not by voltage. For example a pulse duty cycle of 10% may be a small opening dimension, and 20% a larger opening dimension and therefore higher engine rpm. I don’t have the actual duty cycle specs, but that’s the basic idea. Pin 1 (red wire) of the connector appears to be a constant voltage (presumably battery voltage) in start and run; for pin 2 (white/lb wire), that’s for the control pulse pin from the ECM. The ground I’m assuming is done through the parts case contacting to the engine ground. There’s an orientation to the connector, so make sure they match up on both sides.
Note: It looks to me a diy’er could disable that function as a test by just blocking off the inlet and out ports. Don’t use something that might get sucked into the engine of course.