EFI Engines

David G · Sep 8, 2013

I am working on a 94 Corolla with 150K that we got for my daughter. It idles real smooth when warm, but a little rough when cold. I do not think the O2 sensor has ever been replaced.

robgIN · Sep 8, 2013

Oxygen sensors are not a factor on cold start, they are not used until they heat up and start working and the coolant reaches a pre set temp to allow closed loop operation. If you have a cold engine running issue, it is NOT the O2 sensor, more likely a vacuum leak.

ray hofstetter · Sep 8, 2013

Idle air control assembly, sometimes cleaning it works, otherwise, replace....

Anonymous-0 · Sep 8, 2013

You can throw a lot of parts at it before you find the right one. The E in EFI is for "electronic"...94 is usually OBD-I, but some are known to be OBD-II compliant and require a scan tool to retrieve the diagnostic codes stored in the computer.

The link below shows you how to extract the codes.
Toyota OBD Trouble Codes

Flannelman · Sep 8, 2013

Rough idle when cold is a sign of dirty injectors. Have them cleaned or do it yourself and it should run better. When the car is cold it is more sensitive to spray pattern because the cold fuel doesn't vaporize as well.

EFI Engines

David G

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robgIN

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ray hofstetter

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Anonymous-0

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Flannelman

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