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M20B25 Thermostat (housing) question + possible vacuum leak?

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    M20B25 Thermostat (housing) question + possible vacuum leak?

    Hey guys I have a 1990 325i with 250k miles. The timing belt was done 20k miles ago so I am hoping that the water pump was done at that time as well (this was around 2.5 years ago)

    I want to change my thermostat but there is also a thermostat housing that I see people changing. Can someone explain why people change the housing and what is a negative for me if I choose not to? I am used to working on Japanese cars and have never heard of a thermostat housing or changed one.

    My second question is sometimes when I rev my car fast like step on the gas in neutral, it would stutter or hesitate then rev. So if I am idling at say 650rpm, and I step on like hard like 75% pedal, the gas will drop to around 600 and then jump up to the correct rpm. This only happens sometimes. It is random. Sometimes the car does it and sometimes it does not. I do not think engine temperature affects it. If I rev the gas slowly or "normally" it will always work normally with no hesitation or stutter. The engine starts and runs fine to redline. It idles perfectly and the power comes constantly.

    #2
    As to the thermostat housing, it only needs to be replaced is one of the nipples is badly corroded or the threads in it are stripped.

    The hesitation off idle sounds like intake leaks and/or a bad TPS. A smoke test will find any leaks and the TPS can be checked with an ohmmeter.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

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