Annoying clunk/jerk from driveline.. any help?

[jasonbk]

Thanks digger. It indeed has stock intake manifold and motronic. I didn't notice any vacuum spike in on/off throttle in low rpm.

Anyways I went ahead and replaced throttle body gasket, looped throttle body water heater and tightened couple hoses on intake and vacuum increased to 12 from 8 in idle which seems right given I have an aggressive cam.

It idles much better now as well and clunk has been reduced in on/off throttle.

[TobyB]

Below 2500, if you snap the throttle closed, does vacuum spike, or stay low?

Low would make me think burnt valves...

t

[digger]

Reduced vacuum is what cam overlap ala 288 cam does. It can also cause drivability clunky running if using stock cast intake manifold and motronic on a motor not built around that sort of cam

[jasonbk]

Here's an update on this.

So the bucking and weird jerkiness only happens below 2500 rpm - and vacuum test showed that I have very low vacuum (8-9) below 2500 rpm. As I rev it the pressure becomes normal.

I checked rubber hoses to see if there's any sign of vacuum leak but I couldn't find anything - and it's weird that it loses so much vacuum below certain rpm range and regain it.

[DirtyTh3rty]

Mine is bad u-joint as i put the rear wheels off the ground and jolted the shaft back an forwards (turning) and there was play. But my knock happens when say im in first going about 10mph and throw the clutch in it knocks and you feel the jerk a little. If yours is only occurring with the gas pedal then I would check the throttle cable or motor mounts

[jasonbk]

but csb is good right?

Oh yeah, forgot to mention that - when the car was up in the air I could take a peak onto CSB with a tiny mirror and they looked fine. And there was no play whatsoever when I shook the driveshaft on each directions.

[Streichholzschächtelchen]

but csb is good right?

[jasonbk]

Update - I replaced:

New 173 ECU with correct chip from SSSQUID
caps, rotors, ignition wires, spark plugs
adjusted throttle cable
replaced AFM with good working one (old one had loose spring which didn't close the flap all the way)
Checked the throttle body and it was clean without any gunk.
TPS was working properly (both idle and wot)
Since then jerking/clunking is lot better now - but it's still there.

Basically below 3k rpm when I release/apply throttle there is a slight jerk. It completely disappears when the car is cold but as car gets warmer it reappears.


I still gotta:

Test continuity on my TPS and replacement AFM
Clean ICV
Check all injectors

If those don't fix the issue I'm gonna move onto fuel related stuff.

[Northern]

I get a clunk in reverse, sometimes first if the clutch chatters. Pretty much replaced everything on the car and it hasn't gone away, so I'm going for round two on rear subframe bushings/RTABs

[Maddog]

As you know, eventually parts wear/fatigue and need to be replaced. E30s are over 25 years of age and any part with rubber should be replaced, including muffler hangers, suspension bushings, brake line, etc.:grin:

Ditto on checking the engine mounts. My former 1985 318i (gutless wonder) made the same type of noise at takeoff and worsened over time; initially thought my exhaust system brackets were broken.

If your e30 is high mileage, it's good to replace these items.

My "newer" 1988 325is has all new bushings front and rear, engine mounts, CSB, guibo, etc.; did this all when I had an engine build.

I am having my 1997 M3's CSB and guibo replaced this week when I have the rear wheel bearings replaced. Car has over 180k and replacing them as a preventative measure.

[jasonbk]

I actually put new subframe bushings as well when I got the new LSD. Mirror is great idea though - I'll try it on next weekend.

I also put new engine mounts about 2 years ago - they still look good.

[TobyB]

Are your engine mounts good?

t

[doorman]

Check to make sure your CV axles don't have any play in them.
I have one that has a bit of slop. With the car in gear and on jack stands on can turn the rear wheel a bit and the diff side doesn't move.

[turbo55]

You can get a look (although not a great one) of the CSB with the exhaust and shield on if you use a mirror and flashlight from near the guibo. It's not easy to line the mirror and light up just right but I've done it before.

[Kershaw]

That sounds like either the center suppor bearing or the rear subframe bushings. Check the csb first. I get it's toast.