1991 bmw 525i dont like the cold weather
 

I have a 91 BMW 525i 5 speed! It will run fine in warm weather but as soon as it gets cold I will start it up to leave work and it will start reving up by its self and stay at a higher rpm then normal untill the engine heats up then it will run fine! Has any one else had this same problem and how can I fix it?

try wiping the error codes on the ECU. may just be that simple. if it doesn't then read the codes that it throws.

Being a 91 model, do you know if it is the M20 or the M50 engine? that was the changeover year

The car runs at higher rpms at idle when cold, to heat itself up faster.

How do you wipe the error coded and what do you mean by change over year? Actually idk if its a m 50 or m 20 how could I tell?

Google the difference, if you don't feel like it - is the intake manifold black and made of plastic or is it silver and made of aluminum. Better yet, if you can. Take a photo of the engine bay and post it on here.

I sure will as soon as I wake up ill post a picture in the morning

Google please. There are lots of very nice pictures of both types of engines online, you'll want to see it. :)

Sounds like you have a vacuum leak , it revs high when cold and when the rubber expands when its warmed up it seals . Spray for vacuum leaks around the intake .

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You may also have a bad temperature sensor (air temp or water temp).

Yet another stupid post.

As other person above me suggested this is most likely a result of unmetered air entering the system. Do a propane/start fluid/brake fluid test or a smoke test if you can.

Temperature sensors would not cause your car to rev it self up to compensate mixture.

Not true, but what i think you are meaning is that the trans shifts later when cold. However, before posting anything like this, you need to know what engine is in the car. if its the M20 engine, it did no have this feature. if its an M50, its actually the transmission that shifts later, it has nothing to do with idling differently. the transmission and engine control units cooperate on the M50 setup, but the M20 is mechanically operated, not electronic. As anybody that knowss how an engine works, raising the idle with no load on the engine is not good for it and creates carbon buildup etc

all of these maybes can be solved by scanning the engine. Both the M20 and M50 have fault diagnostics built into the ECU, why would you start anywhere else?

Just FYI un-metered air, depending where it's at might not throw a CEL code. For example 2-3 bad o-ring on fuel injectors will cause misfire and rev adjustments but will throw CEL maybe once a week.

This is incorrect, at least for the M50 engine. When cold, the car's idle is around 250-300 rpms higher and the gear shift points are also later (for automatics). These two features are there to generate more heat and to heat up the engine faster.

An engine takes anywhere fro 6-10 minutes to reach operating temperature from cold, depending on whether you're idling or driving throughout. Optimal temperatures ensure that the most efficient combustion is taking place and thus the least amount of fuel is wasted (there may be other reasons as well), according to the engine's design.



rgds,
Roberto

i have the m50 engine in my car and i just looked and my vacume hose has a crack in it! I do believe thats whats causeing the problem

Cool + 1

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