Idle Speed Failure on Vulcan Fuel Injected 3L

[Nehmo]

2001 Mercury Sable LS (4th generation, Taurus equivalent), 3L Vulcan (push-rod) Fuel Injected engine (8th character of VIN is U)

The car starts as normally, but once started, it doesn't have the same throttle control that normally keeps the engine running at proper idle speed. If you put no pressure on the gas pedal, the engine will die. If it were an old-time carbureted engine, then I would say the idle adjust is set too low. But on a fuel injected modern engine, I don't know what controls the idle speed.

The problem is not constant. It might work ok, then have the problem, then "fix itself" for a while.

To explain further, the car can be driven normally except when you stop at a light, you need to keep a slight pressure on the gas peddle to keep the engine from dying.

What do I look at to find the problem? What do I need to test?

[harleyguy]

Do you have a check engine light on? It will have an idle air control (iac) to control idle. I was thinking that but then you sit it dies at stop lights. Does it idle in nutral and want to die when you have it in gear or just wants to die every so often?

[Nehmo]

Originally Posted by harleyguy

Do you have a check engine light on? It will have an idle air control (iac) to control idle. I was thinking that but then you sit it dies at stop lights. Does it idle in nutral and want to die when you have it in gear or just wants to die every so often?

The check engine light is on for another irrelevant reason. (I forgot what, but it's not critical.) So, I just ignore it.
But you're right. I need to see if some new code shows up. I'll check it when the sun comes up.
When the problem is presenting itself, it won't idle in Neutral unless I give the throttle pedal some pressure. The same thing happens in Drive with the brake applied. So, when I come to a light, I have to use 2 feet (one on each pedal) to keep the engine running and the car stopped.
Fortunately, the problem isn't constant. That gives me a little time to diagnosis it. Today, the car ran OK.
I'm going to read the codes, and I'll see if I can clean the Idle Air Control.
A $50 USD part.

[harleyguy]

Yes check for new codes and report back. Sounds like maybe just a dirty iac.