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^this.

what sort of equipment do you have?? a vacuum guage would be nice. a scan tool to read o2 sensor voltages would be really helpful to do the propane trick as well.

the propane trick is an unlit tank of gas with a torch tip utilizing a (fuel grade)rubber hose extension to pipe the fuel along intake manifold gaskets, and enywhere else unmetered air could get into the engine creating a rough idle. open the tank about 1/4 turn and move slowly and avoid the maf.

watch for o2 sensor voltage spikes indicating the leak has been found. move away, voltage starts cycling normal again. move back, voltage should spike again.

repair leak.



df
 

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Where is your idle at?

Mine was just plain to low... At about 600 it was rough and bounced around (well after repairing lots, and I mean lots of vacuum leaks). Had BMW turn up the idle to about 850, all is well now!
Of course the higher speed. Old just be masking another leak, but it works.

I'd be willing to bet you have cracked rubber hoses under your upper intake manifold.
 

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^Normal idle is about 650rpm. 850rpm on a warmed up engine is a bit high.
good point, I guess it would have helped if I said that was the cold idle speed. sorry! :)

It does idle about 700ish when warm. which I know is high, but it helped the roughness that I couldn't solve.
 

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Discussion Starter · #7 ·
Propane test? haven't tried that!

The propane test is interesting, I have the propane but I don't have a scanner. I have carsoft, but I don't know if I can read 02 voltage with that.
The Idle is smooth when the engine is cold.
Idle speed is normal (800). if I raise the engine speed to 1000, I still have some roughness.
I have sprayed B12 around the intake and vacuum hoses without seeing a change.
I will hook up the vacuum gauge and see what that looks like.
I will try all of these ideas.
Thanks everyone!
 

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any one that has a high sample and display rate. (baud, iirc) an easyway to check this is to snap the throttle and watch the rpm. the faster that mirrors the actual rpm the better. this should also equate to a similarly faster o2 voltage display.

then just watch for the voltage spike and hold when you locate the leak (if present) along the manifold and ports.

just watch the maf.


df
 
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