Vehicle sputters on cold start on cold mornings

Question

I have a 1998 Ford Explorer with really low miles (< 30,000 miles; classic "little old lady who only drove it to the grocery store once a week" type vehicle).

The first time I start it on cold mornings, while idling the engine will rev up to somewhat high RPM's for idling, sputter for a few seconds, rev up again, sputter for a few more seconds, etc. The engine may even die during one of the sputtering phases. The sputtering is worse the colder the weather is in the morning.

Once the car warms up, it idles and runs fine.

Any hints as to what's going on with it?

Answer 1

On a Mitsubishi, it would be either a failed Idle Air Controller, or the Base Idle Set Screw has backed out and needs to be reset (and sealed into place). Look for something similar to start with.

Answer 2

I'd check for vacuum leaks and malfunctioning idle controller valves. Cold air is more dense (contains more oxygen for the same volume) so I'd expect a vacuum leak so show up worse as you get more unmetered air introduced into the engine and the ECU tries to compensate for the air/fuel mixture being off, which leads to the idle surge.