[tesco]

After work today when I first started my car the RPMs jumped to around 2500, then slowly dropped to around 1500 where it would normally idle in cold weather.
After waiting about a minute for the engine to warm up i started backing out and realized I had to press the brake really hard to stop, because my idle was still up near 1500.
In drive, whenever I would stop at a light the engine RPMs would still be in the 1000s, and the car would try to surge unless I held the brake pedal really hard.
After about 5 seconds of being stopped the rpm would drop to the normal 750.
If I were to move my steering wheel or tap my gas pedal it would again jump to the 1000s then drop to 750 again after 5 seconds.

After I got home I took a look under the hood hoping to find a cracked vacuum hose but didnt find anything. When I restarted the car everything was completely back to normal.

Any ideas? Hopefully a one time thing because of the cold (-20c)?

2004 mazda6 auto 5spd with 239000km

 

[Snowtrax]

Sure sounds like like cold weather. The engine will automatically idle higher to help warm itslef up and as for not stoping as easily there very well could have been ice on your rotors, or the simple fact that the brake fluid would be thicker because of the cold temperatures it takes more to move it through the lines and all of the seals around the pistons and the pistons themselves would be stiffer.

 

[Final Impact]

Less vacuum at high idle (1500 RPM) so the "booster" offers less vacuum assist. Any chance it has a minor vacuum leak somewhere? This would make this issue even worse!

Inspect flex hose and all vacuum lines. Make sure there are not breaks, cracks, fallen off, rotten off, etc...

 

[tesco]

Today the car has been back to normal. :huh:

Less vacuum at high idle (1500 RPM) so the "booster" offers less vacuum assist. Any chance it has a minor vacuum leak somewhere? This would make this issue even worse!

Inspect flex hose and all vacuum lines. Make sure there are not breaks, cracks, fallen off, rotten off, etc...

Low vacuum due to high idle seems likely, not to mention the high rpm would have increased the torque which would mean having to fight that using the brakes as well.

Last night I inspected all the vacuum hoses that I could easily see including PCV valve. No cracks or anything obvious.

Sure sounds like like cold weather. The engine will automatically idle higher to help warm itslef up and as for not stoping as easily there very well could have been ice on your rotors, or the simple fact that the brake fluid would be thicker because of the cold temperatures it takes more to move it through the lines and all of the seals around the pistons and the pistons themselves would be stiffer.

I understand the engine will idle higher to warm up, but I should probably have mentioned my drive home is 45 minutes long and that high idle stayed throughout the entire drive...