Motor serves when cold

Asked by GuruB3KH5 Apr 01, 2020 at 10:14 AM

Question type: Maintenance & Repair

I have a 1999 gmc seirra  when the temperature outside is
65 or below my truck has a rough idle and serves up and
down until temp gauge gets up to about normal I have
changed o2s mass air and temp sensors and no help I
have done everything that I know to do and still the same
any ideas ?

4 Answers


Did you change the engine coolant temp sensor or the air temp sensor? In addition to a bad engine coolant temp sensor, a vacuum leak is the most common cause for this. See this post on surging idle causes :

I just changed the coolant sensor where is the air sensor I dont know much about all these sensors?

Has anyone ever had this to happen or is it just my bad luck ?I dont know what to do I really need my truck but I'm afraid to drive it like this


Surging is caused by the engine not getting enough fuel: running lean, rough idle, and is often caused by a defective fuel regulator or clogged fuel filter, clogged injectors, or a vacuum leak. A rough idle is often caused by old, worn out plugs and plug wires, or maybe defective coils. dong this at moderate to cool temperatures is quite usual, and maybe all you really need is an extensive tune-up.

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