Rough idle when warmer

This topic has 1 reply, 2 voices, and was last updated 4 weeks, 1 day ago by peterd7202.

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March 19, 2025 at 12:36 pm #310037
MtnPriest
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Hello, all —

Looking to know even where to start a diagnosis, if needed.

Car has no codes, runs fine, LTFT fine (about +2%). When the weather is cold, the car has no issues at all.

When it’s warmer, or after I’ve been driving for a long time, so the engine compartment is warmer, the normal idle of about 750-800 drops to around 500 at red lights, and sometimes surges up and down (but no stall yet).

Any ideas of where to start a diagnosis? Short list of things that could be happening?

I’ve cleaned throttle body and IAC, for what it’s worth. Just with totally normal trims and no codes, I’m curious where to start. I can wait for a real problem to occur, but I’m trying to build up my diag and repair abilities, and would love to try to figure this one out.

2006 Ford Focus ZX4, 2.0L 4-cylinder

Thanks!
March 20, 2025 at 2:31 pm #310063
peterd7202
Participant
Most likely one of these, dirty fuel injectors, a faulty idle air control valve, vacuum leaks, or a problem with the throttle position sensor.
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