635csi bogging/ bucking at low RPM

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76fjord2002
Posts: 3
Joined: Aug 08, 2022 7:04 PM
Location: New Jersey

635csi bogging/ bucking at low RPM

Post by 76fjord2002 »

Hey guys this is my first post here and I'm hoping somebody can help me with an issue I'm having.

I have an 85 e24 that I just spent the last two months refinishing the entire suspension and today I finally went to take it for a test drive. I got around the block fine but then after coming to a stop I starting having an issue. When I try to accelerate from stop at around 1000-1800 RPM the car starts to bog and buck. When getting on the gas it almost feels like the RPM get stuck. Once I manage to get the car over 2000 or so RPM it seems to drive almost normal, although just getting the RPM that high is difficult. The issue is also intermittent, a couple times I managed to take off just fine while other times I had to try 5 times or more to get the car going. The car idles fine and revs fine in neutral, the bogging only happens in gear.

I'm very confused as to what could be the issue especially since I was able to drive for a couple minutes fine before. I'm not sure if whatever it is could have to do with the fact that the car sat for the last two months also. I replaced the coolant temp sensor just now as I had a spare but it didn't help. If anyone has had a similar issue or has any suggestions I would really appreciate it.

Thanks,
Zach
1st 5er
Posts: 21718
Joined: Jun 13, 2008 12:15 AM
Location: Cypress
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Re: 635csi bogging/ bucking at low RPM

Post by 1st 5er »

Is your AFM plugged in?

Dipstick seated?
Sounds like vacuum leak.
matreyia
Posts: 64
Joined: Dec 22, 2021 1:05 AM
Location: Houston

Re: 635csi bogging/ bucking at low RPM

Post by matreyia »

Agreed... classic vacuum leak symptom.

Or:
Fuel pump(s) : there are two and the low pressure one may be totally dead.
Throttle Body rare malfunction
Electrical ground issue (unlikely but still possible as I experienced this personally), check alternator voltage output when engine is running.
Fedaykin528e
Posts: 685
Joined: Apr 03, 2008 2:21 AM
Location: Brooklyn

Re: 635csi bogging/ bucking at low RPM

Post by Fedaykin528e »

The exact thing happened to me once and I nursed it to a shop for them to tell me that I forgot to put the oil cap back on. :fool:
matreyia
Posts: 64
Joined: Dec 22, 2021 1:05 AM
Location: Houston

Re: 635csi bogging/ bucking at low RPM

Post by matreyia »

During refinish process did you take of the intake manifold? If so then check the metal tube connecting the manifold bottom with the oil pan top and make sure the spring is correctly in place pushing up the tube into the bottom pf the intake manifold AND that the connections are air tight and seated correctly.

Then check that your dipstick is correctly seated amd not loose. This is after you check all hoses related to air vacuum.
1st 5er
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Location: Cypress
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Re: 635csi bogging/ bucking at low RPM

Post by 1st 5er »

matreyia wrote: Aug 10, 2022 8:47 AM During refinish process did you take of the intake manifold? If so then check the metal tube connecting the manifold bottom with the oil pan top and make sure the spring is correctly in place pushing up the tube into the bottom pf the intake manifold AND that the connections are air tight and seated correctly.

Then check that your dipstick is correctly seated amd not loose. This is after you check all hoses related to air vacuum.
That "tube" is M20 specific.
matreyia
Posts: 64
Joined: Dec 22, 2021 1:05 AM
Location: Houston

Re: 635csi bogging/ bucking at low RPM

Post by matreyia »

Ah... no idea on my part.
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