Rev hang?

[Dawskip]

Idk how to best describe what’s going on, but I’ll walk through the issue as clear as I can. 
 

Currently, when in gear, the engine surges. At idle, I can give it gas, it acts normal, no issues. 
 

If I’m in neutral and I put the clutch in and out, no issues. 
 

when I’m shifting into first gear, even without giving gas, the engine surges to ~3k rpm, and if I give it any gas it essentially acts like in flooring it. 
 

what would cause this issue?

['76mintgrün'02]

I am wondering if it might be a broken driver's side engine mount that is letting the engine twist upward and that pulls on the throttle.  The bracket on the sub frame that the mount attaches to is a known weak point.  The mount itself can fail as well.  The rectangular shaped mounts have a steel stop at the top that keeps the engine from lifting, but the round hockey puck style do not have that feature.  That's the first place I would look.

Tom

['76mintgrün'02]

I just did a search using "broken engine mount throttle" and found these threads.  There are probably some photos mixed in that will show you what to look for.

 

https://www.bmw2002faq.com/search/?&q=broken engine mount throttle&search_and_or=and&sortby=relevancy

[AustrianVespaGuy]

Really the *only* way for the engine to rev up like that is if it's getting a lot of extra air. This narrows things down to just a few places to check:

 - Vacuum line leaks

 - Brake booster/line leak

 - Throttle plate actuation (such as @'76mintgrün'02 suggested)

I don't see an obvious way that the transmission would interact with any of those, but that really is the whole list of possibilities.  Maybe check your pedal linkage too?

[Mike87]

1 hour ago, AustrianVespaGuy said:

Maybe check your pedal linkage too?

I would suggest you check this and your motor mounts as '76mintgrun'02 said above.

Edited August 7, 2021 by Mike87

[Dawskip]

10 hours ago, '76mintgrün'02 said:

I am wondering if it might be a broken driver's side engine mount that is letting the engine twist upward and that pulls on the throttle.  The bracket on the sub frame that the mount attaches to is a known weak point.  The mount itself can fail as well.  The rectangular shaped mounts have a steel stop at the top that keeps the engine from lifting, but the round hockey puck style do not have that feature.  That's the first place I would look.

Tom

After further investigation I think this may be right (amazing guess).

 

I can push down on it with little weight and hear the RPMS climb. I checked the mounts integrity and saw no cracks or anything going to the block and the subframe, the rubber mount appears to be tightened on there pretty good, so I’m not 100% sure what the issue is yet. 

['76mintgrün'02]

Which style mount do you have on the driver's side.  Is it rectangular, or cylindrical?  

 

The bracket is kind of hard to see, because it is tucked in close to the steering box.  Shoving the engine towards the passenger side should make a break obvious.  You can try lifting up on the intake manifold, assuming you have a downdraft carburetor setup.

Tom

[Dawskip]

3 minutes ago, '76mintgrün'02 said:

Which style mount do you have on the driver's side.  Is it rectangular, or cylindrical?  

 

The bracket is kind of hard to see, because it is tucked in close to the steering box.  Shoving the engine towards the passenger side should make a break obvious.  You can try lifting up on the intake manifold, assuming you have a downdraft carburetor setup.

Tom

Looks to be the cylinder one. I jacked it up and looked under and got a decent view of the mount by the box and it seemed good, I have dove 40s on it now. 
 

pulling up on it and pushing down both increase the revs. 

['76mintgrün'02]

Sometimes the mount tears in half, but it could look normal when it is sitting in the at rest position.

 

Sometimes posting photos is more helpful than you might expect. 

 

Photos of the mount and the carb linkage might be helpful.

Tom

[Buckeye]

How long have you had the car and how old or new are your engine mounts?

[TobyB]

Put your jack under the oil pan.

 

OPEN THE HOOD.

 

Lift a bit.

 

If the motor mount's broken, you'll know it.

 

t

 

[halboyles]

9 minutes ago, TobyB said:

Put your jack with a short 2x4 laying on it under the oil pan.

Just in case.

[Son of Marty]

While your checking mounts include the tranny mount just to be sure. +1 on lightly jacking the engine with a 2x4 and inspecting all 3 sides of the mount use a mirror if you can't see the back side of the mount, they all crack sooner or later with out the reinforcement plate.

[kbmb02]

7 hours ago, Dawskip said:

…. I have dove 40s on it now. 

pulling up on it and pushing down both increase the revs. 

 

Post photo of the throttle linkage assembly between the gas pedal lever and the carbs.

[Mike Self]

And if your '02 is an early one (pre 1971 AFAIK) check the right (passenger side) motor mount.  Early cars have a very simple mount bracket that's just a bent piece of steel with no reinforcement.  It will stress crack (the metal bracket, not the rubber mount) and cause the engine to flop around--the usual announcement of a failing right side mount is the air cleaner hitting the hood.  Those early mounts should be replaced with the later and much sturdier welded up mounts.

 

mike