Rough Idle: A/C compressor?

**Hornung418** · 10-12-2010, 12:15 PM

So I've been on the hunt for the source of my rough idle and I think I've got it.

I cleaned my DISA Valve yesterday afternoon and drove around taking as many stoplights as possible. Idled smooth at 600rpm. So this morning I drive down to the post office to mail my throttle body adapter plate back to Turner, and the car is vibrating and dipping to 500-550rpm as she usually does. On my way back I got the brilliant idea to turn the air conditioner off. BAM! Smooth as butter (clunks aside)

What can I do to further investigate my issue? I've done the searching, and all the typical air conditioner stuff about FSR, blower staying on, driver side cold, pass. side warm, Compressor clutch failed doesn't apply to my case. A/C blows ice cold, fan works at all speeds, A/C belt is spinning with what seems to be the same speed as the engine.
Could it be worn belts or bad tensioners? I wanted to keep this with in my build thread but this seemed the best way to get a solid answer.

Thanks!!

**danewilson77** · 10-12-2010, 12:54 PM

Could be tensioner........but it seems like everything else is good to go...unless clutch is acting sporadic....

**chefsboss** · 10-12-2010, 01:06 PM

mmmm. funny, mine seems to idle smoother (albeit higher) with the AC on... Isn't there some sort of something that is supposed to kick up the idle a notch or two when the AC is turned on? ... Curious. But yeah, ^^^ He's usually right, maybe tensioner... that ones REEL easy to change too from underneath.

**Hornung418** · 10-12-2010, 01:34 PM

Okay so I'll swap my A/C tensioner (pt# 11281433571) for a new one. Are they all the same or is there a hydro/mech variation?

**telijah** · 10-12-2010, 02:19 PM

Running the A/C obviously takes a little more juice out of the engine... Is your alternator putting out properly?

**Hornung418** · 10-12-2010, 04:00 PM

What are some symptoms of a poor alternator?

**telijah** · 10-12-2010, 04:04 PM

Well, I suppose a number of things. You should be able to take it to any parts shop and they can test it, usually for free.

**Hornung418** · 10-12-2010, 04:28 PM

I have needed to crank the ignition more than once to start the car every now and then...but I thought that was belt related...I really don't want to buy a new alternator

Or would that be starter motor related?

**telijah** · 10-12-2010, 04:32 PM

Could be either. The starter needs more juice from the battery to turn the car over... if the battery is not supplying enough juice, it may be because the alternator is not charging properly. If you're in an area where it is getting colder already, the problem will probably get worse. I'd take the car down to somewhere like Autozone and ask them to test your battery and/or alternator. They usually will do this for free.

**aka fonz** · 10-12-2010, 04:38 PM

well if it was your alternator, anytime something extra electrical that is used, ie: lights, blinkers, radio ect you would see a dramatic change in idle... cranking would have nothing to do with it. The battery is used to start the car, the alternator is used to keep the car running. If it was dead, you'd know.. you wouldn't be driving.
Every car I've ever had has had some sort of idle variance when AC is engaged, it must be due to the extra parasitic drag. The dip usually occurs when the clutch on the compressor is engaged during it's cooling cycles. The car doesn't feel like it's going to stall does it? AC weather is long gone here in NE

**Hornung418** · 10-12-2010, 04:43 PM

I'll get a video up soon. I think you're missing my point. The idle is sporadic and violent, not higher...

**aka fonz** · 10-12-2010, 04:45 PM

no I think I do.. are the RPMs dropping while the AC is ON, or the opposite..

**Hornung418** · 10-12-2010, 04:48 PM

They drop to 500 and bounce up to a grand, shaking the car and causing a clicking sound to be heard from the engine bay. It's not normal. You'll see. BRB.

So the guys at AdvanceAuto couldn't directly test the alternator because the battery is in the trunk...but the battery checked out at 814/850...good right? The alternator is fine because of the fact that battery is good. True story?
I managed to shoot a video before I went down:

Burble in question is as soon as the AC is turned on, but she's shy, so naturally she didn't do it again

**danewilson77** · 10-12-2010, 06:23 PM

Originally Posted by Hornung418

Okay so I'll swap my A/C tensioner (pt# 11281433571) for a new one. Are they all the same or is there a hydro/mech variation?

Only mechanical option for the AC pulley...no hydraulic...

**Hornung418** · 10-12-2010, 06:29 PM

Have any issues with going aftermarket for this particular application ?

**brian2305** · 10-12-2010, 08:34 PM

Try cleaning the iac?

**Hornung418** · 10-12-2010, 08:53 PM

Couldn't get my brake booster vac hose off the upper intake boot...so no

**slvrXI** · 10-12-2010, 08:59 PM

There was a DME reprogram bulletin that was to help eliminate fluctuating idle, especially with high load (ie. seat heaters on, ac on, power steering under load.) Do you have a rough idle or a fluctuating idle?

**Hornung418** · 10-12-2010, 09:16 PM

Difference between the two?
Ummmm the tach doesn't bounce, but dips every so often and violently shakes the car. This is especially noticeable in the mornings on cold start-up.

**slvrXI** · 10-12-2010, 09:22 PM

rough idle would include vibration or misfire symptoms. Idle fluctuation would mean the car runs smooth, but the idle does not stay at a specific RPM the whole time. A "dip" would be a fluctuation. Chances are your ICV may be dirty, or your software needs an update. I had the same issue, only when the AC is on would the idle act up. It would dip down low every so often and occasionally the engine would stall. I replaced the ICV, no change, I raised the idle, no change, finally I updated software and the problem went away.

**Hornung418** · 10-12-2010, 09:28 PM

Hmmm well the dealer states that I don't have any outstanding campaigns...When I get my M54B30 intake manifold we'll see what the damage is.
Any other thoughts as to why the engine makes noise coming from the pass. side? Freakin gremlins...

Also I could not for the life of me get the darned Brake Booster Vac Line off the upper intake boot...Any tips?

**meangreen94z** · 10-12-2010, 10:14 PM

If your talking about vibration at idle, your tensioner and alternator dont have anything to do with it. The compressor activating is putting a load on your engine at idle, which is normal. The reason it feels excessive is likely sunk/worn engine mounts. They make a drastic difference on an E46. I've replaced them many times on customers cars, my dads car, and my personal car for this issue. The difference is night and day on older/higher mileage cars.

Originally Posted by Hornung418

Hmmm well the dealer states that I don't have any outstanding campaigns...When I get my M54B30 intake manifold we'll see what the damage is.
Any other thoughts as to why the engine makes noise coming from the pass. side? Freakin gremlins...

Also I could not for the life of me get the darned Brake Booster Vac Line off the upper intake boot...Any tips?

Use a pick, stick it in the lip on the boot and work around the plastic nipple while pulling on it, it will generally come loose

**Hornung418** · 10-12-2010, 10:36 PM

Originally Posted by meangreen94z

If your talking about vibration at idle, your tensioner and alternator dont have anything to do with it. The compressor activating is putting a load on your engine at idle, which is normal. The reason it feels excessive is likely sunk/worn engine mounts. They make a drastic difference on an E46. I've replaced them many times on customers cars, my dads car, and my personal car for this issue. The difference is night and day on older/higher mileage cars.

How can I look for them? I've never replaced or even thought about them...As far as replacements go, which do you recommend?

Use a pick, stick it in the lip on the boot and work around the plastic nipple while pulling on it, it will generally come loose

Man I tried a flathead for about a half hour...gave up and wiggled my DISA out around it. I'll have to get a pick and work at it this weekend. Also it's got cracks at its base...so I'm going to replace both of them anyways. I'll prob just cut them out.

**meangreen94z** · 10-12-2010, 10:57 PM

The center metal/rubber square on the mount that the engine arm sits on will protrude about 1/2" from the dome on a new mount. A worn mount will start to sink, sometimes to the point the arm is sitting on the dome. Its best viewed from underneath, but if you have 185k on a 10 year old E46 with the original mounts I can guarantee you that their replacement will be beneficial. I had 130k on my car when I got it and sitting at a light the whole interior would buzz/vibrate. After I replaced them I couldnt tell the engine was running. I'm a bmw tech so I've always just used the original part.
Yeah I just use a thin pick and work around it while I pull/twist on the nipple.

**Hornung418** · 10-12-2010, 11:33 PM

IDK where you got 185k from...but I only have 105k.
When I take care of my Tranny mounts, Flex disk, Center mount and Subframe bushings this Thanksgiving, I'll give the mounts the business as well

Just to clarify, this is only a vibration issue which doesn't affect the driveablity or engine components, correct?

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