Low idle until warmed up


#1

I have 98 Taurus - 6 cylinder - 3.0 liter (SOHC engine). Car starts fine but idles extremely low (almost stalls). As the car warms up, the idles seems to get better. A few years ago I replaced the IAC valve because of the engine racing (which upon replacing the IAC, it’s been fine since). Any other ideas ?? Car has over 160K miles and had a rebuilt engine dropped in a few years ago so this engine actually has ~ 100K miles


#2

Is the CEL on? My guess is the coolant temp sensor is sending bad info to the computer, making it think the engine is warmer than it is. The computer is, therefore, not adjusting the idle speed and fuel mixture to compensate for the cold engine, similar to the choke function on old-fashioned carbs.


#3

The engine is running, either rich, or lean during warm up. To determine if it is overly rich, when the engine is cold, pull a vacuum line on the intake manifold or intake tube. If the idle improves, the air/fuel mixture is rich.
The engine computer adds fuel by its reliance on some sensors: engine coolant temperature sensor, and the intake air temperature sensor. If these are signalling temperature colder than actual, the engine computer will add more fuel.
You can check the accuracy of the sensors by measuring their ohms and volts. Instructions on doing that are in the repair manuals, and here: http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c1528003aabf for the coolant temp sensor;


#4

No CEL on at all.