Rough Idle - When Cold

[the_bends]

92 Legacy Turbo, 4EAT has a rough when it is cool outside. It is really quite rough. The idle speed seems to be normal. It starts around 1500rpm when cold then slowly drops as it warms.

Problems seems to start when the temp is around 32F and colder. Once the engine warms up for about a minute it is fine.

The car had been sitting for a year but I have put it back into service recently with a fresh oil change (5w30), new coolant tank (topped up coolant), new starter, fresh tank of gas. It was okay when it was warmer outside. There is no CEL...

Bob

[VRoman]

I have the same problem with my 94 Legacy. When the engine is cold, let say less than 60 degrees, idle RPM drops to 400-500 for some time, then revs up to 2500-3000, and then slowly goes to 1300-1500, after what it immediately drops to 400-500. It's running so rough that it seems like engine is running on 2 cylinders. Sometimes engine dies before it revs up again. It repeats this cycle several times, and after about 2 minutes it stabilizes at about 900-1000 rpm running smooth. Another minute, and the car is ready to drive with absolutely no problems. This idle problem appears every several months and disappears on its own a couple weeks later, and I still haven't figured out what causes it. I don't see any possible vacuum leaks, and there is no "check engine" light. Could it be a bad MAF sensor?

[VRoman]

Thanks to Legacy777 I solved my problem by replacing coolant temperature sensor. http://bbs.legacycentral.org/viewtopic.php?t=21297 I never thought that a malfunctioned temperature sensor could cause so much trouble.

[Legacy777]

cool, glad you got it fixed.