What's this idle problem?

[ScottyWM]

E34 M50:
Couldn't find this problem searching, probably because I couldn't think of a good way to describe it. Just started a couple weeks ago, but last two days it has been much worse. What happens is that as the car slows to a stop, the idle goes up and down like it wants to stall. It never actually has stalled. But the idle swings from about 650 (normal for the car) to about 500 as the car is rolling to a stop and for the first couple seconds that it's stopped. Then it stops swinging. The 'swing' is about 1 second at 650, 1 second at 500, repeated until the car comes to a complete stop.

At first it wasn't doing it every day or all the time, last couple days it seems to do it all the time. I'm getting no faults. Pretty sure I don't have any vacuum leaks as I've checked this recently. I'm wondering about the O2 sensor, even though it was new 40k ago. Any ideas?

I was just bragging about how I haven't had any trouble for a looong time. Guess I jinxed myself.

[winfred]

check the two lines coming off the front left side of the valve cover, they rot off under the intake and cause **** like that

[ScottyWM]

Nope, both of those look okay. Replaced the smaller one just a couple years ago.

I did just notice this, looks like a hose should be here, but this is blanked off. It's just to the right of the throttle housing. Must have been like this since I've had it (9 years). Is this supposed to go somewhere?


So anyway, I just adjusted this screw out a little bit and got the idle back up around 800. So far this works good. But I bet the computer will make an adjustment to compensate once it "learns" what I did. I'm probably causing trouble, right?

[winfred]

i think they put that nipple on the booster check valve so they can sell you a new check valve when you snap that tit off, never seen anything hooked to it. as for the throttle adjustment it's usually not a good thing as it may not let the computer go into idle mode (doesn't know that the throttle is closed so it doesn't trigger the icv circuit on) your mileage may vary

[scott 4991]

I use that nipple to check vacuum - just as a reference. Mine has always been plugged.

sc

[ScottyWM]

Well crap... looks like I'll have to adjust the throttle screw back to where it was. Kicked up both a check engine light and trans program error this morning at a stop light after about a 15 minute drive. Shut the car off and restarted, errors were gone.

[ryan roopnarine]

though this might be obvious to winfred, you either have a gross air leak, or have something wrong with your throttle body, ICV, MAF or TPS if you get the check engine light combined with trans program. i'd suggest starting off by checking the hoses and gaskets with carb cleaner for leaks, making sure that the bore of the throttle body is spotless, and making sure that the spring on the throttle body is REALLY pulling the plate back to close position at idle (mine wasn't). then lubricate the TB linkages.

[ScottyWM]

Okay, Put the throttle screw back and have been driving the car. Still have the original problem, but at least no scary errors. Did the stomp test and got 1216 - TPS. Checked the sensor as per Bentley, got nothin'. Tried again and again, got nothin'. Put the key to "on" (not per Bentley), and got the correct values once, then nothin'. Tried key off, on, off... nothin'. I can't clear the 1216 code either, will it not clear until I replace the TPS?

So looks like you're right... TPS. It was an intermittant problem at first that just kept getting worse, so that makes sense. Wish I had one to swap out before paying $70 for the damn little thing.

Thanks for the help guys.

[billb]

Okay, Put the throttle screw back and have been driving the car. Still have the original problem, but at least no scary errors. Did the stomp test and got 1216 - TPS. Checked the sensor as per Bentley, got nothin'. Tried again and again, got nothin'. Put the key to "on" (not per Bentley), and got the correct values once, then nothin'. Tried key off, on, off... nothin'. I can't clear the 1216 code either, will it not clear until I replace the TPS?

So looks like you're right... TPS. It was an intermittant problem at first that just kept getting worse, so that makes sense. Wish I had one to swap out before paying $70 for the damn little thing.

Thanks for the help guys.

Part number is 13 63 1 721 456. That's not a good number anymore, but I think it'll work on your car fine. I can bring it by tomorrow if you want to check it out. Yours if it works.

[ScottyWM]

Great, I'll take you up on that! BMA show the same BMW p/n for our two cars. Your p/n doesn't match the www.realoem.com p/n, but I'm with you, it should work - worth a try.

You want to come to my work or I can come down to yours? Just email or call me at work.

Scott

Part number is 13 63 1 721 456. That's not a good number anymore, but I think it'll work on your car fine. I can bring it by tomorrow if you want to check it out. Yours if it works.