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Old 12-09-2016, 10:21 AM   #1
Scooby Newbie
Member#: 136062
Join Date: Dec 2006
Default Engine extreme high idle

I have a 2005 Forester X, normally aspirated, 5MT, with 175,000 miles. Under certain outside temperature conditions, the idle will run up to 3000 RPM. I can "blip" the throttle and it comes back down to normal. This seems to be an "idle" even though the RPMs are so high, because when the car is in gear, it has some additional power, but it is definitely not trying to maintain 3000 RPM, which would be about 70 mph in 5th gear. Instead, it just does not slow down as fast as normal when I take my foot off the throttle.

In addition, something the car stays at 1200 RPM even though the engine is completely warmed up.

The problem seems to be temperature related. It does not happen in the summer, but seem to be most prevalent when the OAT is about 35 - 40F. It also does not happen nearly all the time. There are no CEL errors.

Reading through the forum, there are several reports of idle surging, but there did not seem to be a single common underlying cause, nor a report that was a good match to this condition. Because of the temperature relationship, it makes me think a sensor is going bad, or maybe the wiring to some sensor has an occasional bad connection.

Advice on things to check are appreciated!
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Old 12-09-2016, 01:41 PM   #2
Scooby Guru
Member#: 60324
Join Date: Apr 2004
Location: a pillow.

probably wouldn't hurt to clean your throttle body. do you have an IAC or DBW? if you have iac might as well clean that too. to my knowledge these cars use the coolant temp sensor to dictate cold start conditions, might want to test that sensor. also did you bypass the coolant lines on your throttle body?
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Old 12-13-2016, 09:43 AM   #3
Scooby Newbie
Member#: 136062
Join Date: Dec 2006
Default Extreme high idle

I will have to check on the IAC vs DBW. If I have an IAC, I will clean. Seems like that could not hurt after 175K miles.

I have not done anything with the coolant lines, but I will check the coolant temp sensor.

Thanks for the recommendations!
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