Rough Idle?

[xgeetx]

Hey guys,

 

I have a 1998 328i. I started to have a rough idle that at one point threw a misfire code. The engine also sputters (sometimes) under load at low RPMs, less than 1500, pretty much in all gears. I replaced the spark plugs (since I hadn't since I bought the car), and they all looked okay, except one had a bit of oil on it (not much). The rough idle continued and at one point my car died after I started it. I discovered large cracks on my air boot and the ICV hose. After replacing both I still have the rough idle issue, but it never dies. The RPMs drop to ~500 or less and the car shakes a little bit and sounds like it's about to stall... but it never does. Does this sound like the spark plug coils or something like a dirty ICV? 

 

If the best option is to move the coils around and see if the misfire follows it, does anybody in the Milwaukee area have a code scanner they would lend me for a day or two so I can try to figure it out?

 

Any help would be great!

[B C]

Clean/replace the idle control valve and look for other intake leaks. 
Is the CEL on? 

[xgeetx]

Yes CEL is on. Only code is a Cyl 4 misfire. I used to have an EVAP code for the longest time but that hasn't shown up in a while... would that have been fixed by my intake replacements?

[B C]

Dont rule out a bum fuel injector when chasing a misfire code

[xgeetx]

Could a dirty ICV cause a misfire?

[B C]

Not directly

[Jeff]

Test your fuel injector. Should have about 16 ohm on it check for pulse it it is in spec.

No sensor will cause a misfire on only 1 cylinder.

If it is a harsh misfire it is ignition related if it is a soft misfire it is fuel related.

[B C]

Good way to put it jerf

[Jeff]

I hope so I had to put my brain in this one

[6670charger]

Mine was going through rough idle (88 E30) a few months back. Finally cleaned the IACV and have had no issues since. A couple of other things I had going on at nearly the same time were a bad fuel pump, and a leak in the main rubber fuel feed line under the hood. Got all of those issues taken care of, and now she purrs like a kitten. 

[patsbimmer1]

Pull your coil for the misfire cyl and check the boot VERY carefully.  If the boot is cracked or brittle it can cause a misfire but it is usually under load.  I have had one severe enough to cause a rough idle and severe misfire.

[xgeetx]

Thanks for the responses. I'm gonna grab a coil today and just see if that fixes anything... after that I'll look into the injectors? Before I replaced my spark plugs I had a misfire on Cyl #2, but didn't put the coils in the same spots (I intended to, but caught myself mixing them up after it was too late).... so I have a sneaking suspicion it is the coil, and it's a relatively inexpensive and cheap fix.

 

Another question: between the air filter box and the MAF sensor there's a pretty large/thick O-ring that fell out. Where exactly is that supposed to go? Maybe I didn't completely fix my intake problems...

[xgeetx]

Mine was going through rough idle (88 E30) a few months back. Finally cleaned the IACV and have had no issues since. A couple of other things I had going on at nearly the same time were a bad fuel pump, and a leak in the main rubber fuel feed line under the hood. Got all of those issues taken care of, and now she purrs like a kitten. 

 

HOw would you describe your idle? I've read that some idles are the engine revving very high. Mine is ~800 and drops towards ~500, oscillating between them. (before I fixed my air boot and ICV hose it would sometimes just stall).

[B C]

If its what im thinking, that o-ring is upstream of the MAF and wouldn't impact drivability as far as being an intake leak. It would potentially pull unfiltered air through and cause extra air turbulence but wouldnt be the cause for an idle-hampering intake leak

[patsbimmer1]

 

#4?

[patsbimmer1]

I think that could cause a drivability issue.  At that point you are losing metered air which could cause the AFR to be off.

[jc43089]

He is talking about the oring that fits into the airbox where the MAF connects.  There are tabs that hold it in.

[xgeetx]

jc43089 is right about which one it is,

 

That O-ring came out, and my tabs have since broken. I think I mounted the O-ring incorrect (on the outside of the MAF lip), which made the tension in the tab holders too high and snapped it Zip-ties do the job fine, but the O-ring is maybe supposed to be inside the air filter box half?

[jc43089]

It goes inside the airbox then you insert the MAF.  My OE airbox had one of the clips broken, I run a K&N CAI now for racecar sounds!

[xgeetx]

Nice. Let me know if I say this right....

 

 

'cause racecar?

 

Replaced the coil, issue fixed! No idle oscillation/shaking. My car still idles just above 500 -- is that normal or does that mean I should go ahead and clean the ICV?

[jc43089]

Idle should be about 650 when warmed up I think.  Because of all of the issues I would unhook the battery and short the cables together to clear the ECU.  It adapts to/remembers things.  When I swapped a light flywheel into a late e36 it idled like crap when first started, surging and hunting.  Then we cleared the ecu and it ran perfect.  It just has to adapt to the new operating conditions.