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Hesitation/bucking between 1k and 2k rpms. HELP!

12K views 35 replies 8 participants last post by  peytonracer4 
#1 ·
As I was going to work today my car started doing this. In every gear under decent load my car bucks forward. It's very noticeable. It's not just a slight hesitation. It almost feels like the clutch slips and grabs again. But it only happens at this rpm. Between 2k and 3k
What could this be :(
 
#8 · (Edited)
How many miles you have. When did you get it and what do you drive like?

Could it be your clutch slipping? Sure. Park in front of a wheel chock and try to start off in fifth gear. If you stall, your clutch is fine. If you don't stall, I guess you'll start loosing your clutch. If it's clutch.

I'm not sure how sure you are this is a clutch issue though. Intake boot or other major intake leak would make you feel a sudden loss of power while the car tries to figure things out. If this disappears when you drive without the maf, that narrows it down to maf or intake leaking somewhere...in the intake or in a vac line.

I'd start there, but if you have more details about your sense of things, I'll try to make up more stuff for you!
 
#9 ·
I got it two years ago. I drive... Normal. I'm honestly a pretty conservative driver but I'll definitely get on it every once and a while.
I only said it sorta feels like a clutch slipping then instantly grabbing. I can still burn rubber though. So I feel like if the clutch is strong enough for that then it should be a clutch. Correct me if I'm wrong.
I replaced the upper intake boot recently. Soon after I got an even louder intake whistle. I looked at the lower one yesterday the best I could without taking anything out. I touched it and moved it around. This could've caused a rip or something. I was really messing with it. It felt new.
So I have to have a vacuum leak somewhere. It's possibly the lower one and I just missed something. After I messed with the lower boot I drove for close to 70 miles without issues. The bucking just started today.
 
#10 ·
If your lower boot is moving around, that could be your issue and you might as well get a new boot and replace it. For $12, you'll be there anyway.

Also, you might broaden your work a bit and clean up things like the icv and TB with appropriate cleaners. I wrote about all the work I did to take care of my idle surging. Search for me and 'maf disa icv tb grommet'

It shouldn't be loose, and that could certainly be your issue. The maf doesn't know about the air coming in past it, so the fuel isn't what it's supposed to be. Eventually, the O2 sensors seem to catch up and call for more gas.

It's not so out of range yet that you haven't thrown codes. If it gets worse, you have too much air and won't be able to get the mixture right...then it seems you would get a code. I'm not positive, but I think you'd get either a maf code or an O2 code.

Sorry...I think you need to go deeper.
 
#13 ·
If it runs better without a maf, that means it's either a maf or intake leak issue. One of the two. But, clean the maf and it's electric connections first before buying a new maf ...and don't buy a maf without checking back here.

It doesn't sound like a fuel filter, but if you haven't replaced yours in years, it'd be a good idea anyway. I got an extra 1.5 mpg or so when I did mine...just by doing that one thing!

I reread what you did with the lower boot...and I guess you moved it, it wasn't moving around loose...is that right? If you moved it, you may have cracked the elbow to the icv to slipped it out of its proper orientation, but if it was on tight, you shouldn't have been able to really move it at all. If you moved it without loosening up the clamp, then we're back to that as a likely suspect again.
 
#15 ·
update: i just drove it with the maf plugged in and unplugged. it's the same both ways. the bucking doesn't go away with the maf unplugged. i did notice that it only does this when the engine has warmed up. i couldn't make it hesitate with a cold engine.
so does this rule out a vacuum leak causing this?

help :(
 
#16 ·
I think you've only ruled out the maf at this point. The maf goes to factory settings, so would run better if the maf is bad/dirty. But, given your symptoms, especially the hesitation only when warm, it makes me think an intake leak is likely.

That said, there might be other things I don't know of that are 'warm related.'

I believe the computer takes in temp readings from the outside air temp sensor, the intake air temp sensor at least in calculating the right amount of fuel; I don't know that they'd cause hesitation if they're 'off' but maybe.

You specified an rpm range for your symptoms. Have you checked to see whether you still have the issue when accelerating hard in third, say, from 3-4K rpms?
 
#18 ·
I think it's a 6mm socket that fits on the screw clamp...if you haven't figured that out yet. Just loosen it up a turn or two then rotate it to the top of the boot.

I hope you find a crack...and hope you won't hate me if you don't! You shouldn't trust people on the Internet, you know...especially me!:lmao:
 
#20 ·
I assume it threw a code when you ran it without the MAF?

It sounds similar to the problems I was having when I forgot to reconnect my intake cam sensor, but that failing should throw a code too.

Would a bad PCV valve cause enough of a vacuum leak to cause a problem? (thinking of that whistling problem)
 
#24 ·
That actually makes sense. If you only started the car once with it unplugged, it may not throw a code (I think the OBDII requires the code to appear over two cycles/starts before illuminating the light).

If you do have other codes, maybe that will help with the diagnosis. How many miles did you say were on it?
 
#26 · (Edited)
Damn, did I miss that evap issue earlier in the thread. If so, sorry!

I'm pretty sure evap works on the vac system. I don't know the specifics, other than that it needs to be able to seal itself to test that it can hold a vacuum...and thus know it's not leaking gas fumes into our atmosphere.

The solenoid code you have might be solenoid, but it could just be a leak. The car might think it's a solenoid issue because that's the first place it registers the issue.



I'll get the realoem diagram for my car up soon, but if I'm right, a cracked hose would cause your issues...and would also maybe explain why you're not seeing it outside of a narrow rpm range.



While wandering around realoem for you, happened upon this...a connection between an evap code and the vac system. that could be the system to look for a crack in. I'm guessing...please wait for someone that knows better!

http://www.realoem.com/bmw/showparts.do?model=AM53&mospid=47723&btnr=13_0633&hg=13&fg=15

 
#27 ·
Thanks Doug. I'll look at it when I'm home. I feel like of that's the issue then I will be amazed. I've had this evap code for as long as I could remember and I've never had this hesitation issue.
I'm not really sure what I'm looking at in that last diagram. Is that thing the tb? And are both those lines the vacuum hoses?
And do you still say it's not possibly a fuel filter? I don't see how it could be, when it only happens when it warms up. But I don't want to rule it out if it's a possibility.
 
#28 ·
You know I love low odds things, and if you haven't done fuel filter, or know you've gotten a lot of gas from dicey places, then you should anyway. But I'm not seeing why only in that rpm range.

The code may have been there for a long time, but the issue is becoming worse...if it is a cracked hose, that'd be expected.

Yes, for my car, that hose is to the TB...thus directly to the intake somewhere. Not on the TB itself...probably on yours (think it's newer than mine) you'll have an F tube off the upper intake boot. One line goes to the fuel pressure regulator, I think, the other to the brake booster (I think). I'd suspect the one going to the fpr does so by way of some valve. It might be under the cabin air filter housing, but I don't know for certain.

Check realoem for your car...it will have different plumbing!

Search F tube, fpr. Maybe I was wrong about the evap code...you might still have an issue with that if it doesn't connect directly to the vac system. Search the diys; there may be a connection off the line leaving the upper intake to fpr, but I'm just guessing.
 
#29 ·
Well I looked at (what I think is) those hoses today. And no dice :(
The line coming from the brake booster line but not going to the brake booster isn't cracked as far as I can tell. So I'm stuck. It REALLY sounds like I have a vacuum leak when I drive. My car isn't even running right now because I fear if I put my intake boots on someone will say to check something else and I'll have to remove them again.
My only other bet is to take it to the dealership. I've never had to do this with a problem in this car where I couldn'tfix it myself.
Please someone save me :(
 
#32 ·
So first, I'd go back a bit. We've asked for codes, you have some but didn't clear them.

When you get codes, you'll get some active, and some that are stored, but aren't throwing a cel...they're still codes.

Autozone reads codes for free, and they'll clear them. Get your codes cleared, start car, check codes again.

Check the e-box, specifically the Kalim fuse, as it, I just learned two days ago, controls a number of odd relays, there's a fuse there in that same fuse pack for the vanos...just check to see the connections are clean and not corroded and that no fuses are blown.

Check the wires from the sensors that are signaling an issue...but get current codes.

Finally, if you haven't removed the cabin air filter housing yet, I'd do that...T-30 bit I think. Underneath is a nice collection of hoses and stuff you might not have looked at, and it's easy to get off and check.

Beyond that, I think I have to say look in the regional forum for a local with good computer and knowhow! Sorry.
 
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