Z4 Rough Idle for 10 seconds when starting

We've owned a 2007 Z4 3.0i for a little over a month now. I've consistently noticed a rough idle for about 10-15 seconds when starting after the car has been sitting (either over night or after several hours of cool down). Sometimes I hear a vibration, but no knocking as described for some N52's. I do hear the fuel injector solonoids tapping, but that's normal. We run 92/93 octane always. 35,000 miles on the clock.

Maybe time for new plugs ... You're almost there mileage wise.

You may also want to pick up a couple of 10oz bottles of Techron Concentrate and run two tanks back to back.

Thanks for the replies. So it doesn't sound like this is something major, just a little maintenance issue. I'll start here.

I had the same weird cold start issue. I brought the car in to get a cup holder replaced and told the service manager about it. He said they would reset the cpu of the car so it could relearn. well he called me after I dropped the car off and said that they are going to replace all the lifters - I didn't have aloud knock or anything like that.

My warranty ends this September, and he said he's seen this type of problem before and it lead to loud lifters etc.

i would take it in!

So I called the dealership and talked to a service guy. He said it sounds like the issue is related to the VANOS adjusting upon startup and that it's completely normal. He did not seem to eager to bring the car in. He asked if I had any lights.

I had something somewhat similar happen the other day. I started my car and it seemed to have a somewhat weaker start and after it fired idled rough and didnt want to rev. After about 30 secs went away and drove fine. First time iv e had tht and hasnt happened since.

Run some Techron or better yet a can of BG 44K through it. May clean it up.

Bob

Thanks Bob. I can't find that techron stuff locally. My indy mechanic carries the BG44k.

Originally Posted by netster

Thanks Bob. I can't find that techron stuff locally. My indy mechanic carries the BG44k.

BG 44K is pretty expensive, but it is great stuff and it will clean things up pretty good. Be careful and don't get it on the paint! Techron is made by Chevron and is a great fuel system cleaner and available at many autoparts stores. Walmart may or may not have it.

I seriously doubt that spark plugs are the issue judging by your mileage.

Just my 2 cents. Good luck with it.

Bob

It has to do with loss in fuel pressure when the car sits for a long time. It takes several seconds for the lines to pressurize and the car run right. There is a valve in the lines that is suppose to hold pressure when the car is off.

I just experienced this for first time today, starting up the Z4 after a couple of months on the battery tender in my garage. It was really rough idling, and the "check engine" light came on and stayed on. After about 30 seconds I shut it off and re-started it. No more rough idle and the check engine light did not stay on. Drove it around town today and it seemed normal.

Not sure if this is the same, but on occsasion mine will surge up and down a bit prior to smothing out. I'm going to give the techron a shot. Aside from that, it runs fine.

I bought my 07 Z4 3.0si in February. The car runs great and looks great. The only annoyance for me has been the idle when I first start the car. Cold start or warm restart- it doesn't matter. The engine starts fine, it is just that the idle speed hunts around for the first 5-10 seconds and then settles down. After that 10 second period, it idles and runs perfect. I ran a couple of bottles of Techron through the gas tank and it seemed to help the cold start idle a bit, but didn't do much for the warm restart. I was perusing the threads on all BMWs with the N52 engine and came across a DIY for cleaning the VANOS solenoids. It doesn't take long to do, but the engine needs to be cool. I'm too impatient and as soon as I found this thread I pulled the intake VANOS solenoid out and blew it out with shop air. Since I had just parked the car about 1.5 hours before, the engine was still hot. Okay, I have a couple of light burns on my hands now, but I hate to wait. The solenoid is on the front of the engine and is fairly accessible in our Zs. I had to use one of my wife's old compact make-up mirrors to align the solenoid and get the bolt started when I put it back in. The intake solenoid is at the top of the head and has no direct line of sight because of the radiator shroud.
Results: Good. The first start after cleaning the solenoid was normal. The idle speed fluttered just a tiny bit. (Keep in mind that my expectations are that the engine speed will surge as soon as the engine starts and settle immediately at the correct idle speed and remain there stable and strong.) I drove the car around and it ran very well. I waited 45 minutes and did a restart. Perfect. I know from my few months of driving the car now that this is the situation where the idle would do the most hunting upon restart. Where the speed would be fluctuating the most during this first 10 seconds after starting before settling down. Being impatient like I am, I plan to try a cold start first thing in the morning before I have even had my coffee. My car has very low miles, so maybe the solenoid had a little sludge build up from so much sitting.

Cold start this morning was perfect. So cleaning the Intake VANOS solenoid did the trick!

Tony, my 2006 Z4 3.0si with 30k miles has a slightly rough start when cold. I thought it was normal. Can you post a link to the post you mentioned on how you clean the VANOS solenoids? Thanks.

Here are the links that I found. These show pix of the N52 engine but in the 3 series, I think. So the engine and location is the same, just that under the hood can look slightly different from the Z.
ttp://www.e90post.com/forums/showthread.php?t=486201&page=3
http://www.e90post.com/forums/showpo...19&postcount=2
http://www.bimmerfest.com/forums/sho...ght=rough+idle
http://www.e90post.com/forums/showthread.php?t=486201
When all is good, BMW engines are the smoothest engines out there- from start up to redline. My X5, M54 engine, has a perfect start and smooth idle. That's why I was annoyed about the rough idle on start up with my Z. I was going to have the dealer look at it next week when I take it in for an oil change, but I had an epiphany yesterday and thought about looking on the BMW boards where the N52 engine is used on other platforms. The N52 engine is also used on the X5 and 3 series for certain model years. These forums are great. The shared learning experiences saves us all in time and money.

Tony, Thank you! I'll do some research.

Update: Idle immediately after cold start is still good and strong. Warm starts degraded a bit when the outside temp hit the 90s last week. If the outside temp is in the low 80s or cooler the warm start idle is still pretty steady. So I called the dealer and described the symptoms- idle speed surges and drops for the first 5-10 seconds and then smooths out only when the weather is hot now. They told me, "no codes/no lights, don't bother to bring it in."

I have the same issue. My 2008 3si shows rough idling when starting engine cold. it lasts about 10 to 30 seconds and engine warms up and idle settles down to normal range, the rogh idle goes away. i have only 17k miles on my z. Used chevron cleaner but no improvement.
I think i heard that 2008 engine has no vanos? is that true? if so what else can be the cause?

well. i checked out my emgime. I do have venos sensors. I cleaned them up with compressed air and maf cleaner but it did not fix the idle problem. Is this supposed to be like this? This is my first bmw so i dont know.
when I start the engine, rpm starts above 1000 then slowly goes down to 520. but unlike other cars (like my jeep or honda) while rpm settles down it fluctuate little bit, like 1200 - 1000 - 1100 - 900 - 1000 - 900 - 800 .......
my other cars are like, 1200 - 1100 - 1000 - 900 - 800 ........ no fluctuation.
Are bmw engines different from other engines this way?

I had the cold idle issue. It would last for a very short time on cold starts. I put 1/2 of a can of Sea Foam fuel stabilizer in the gas tank and the problem is gone. I'm thinking that it was dirty fuel injectors. For the price of a can of Sea Foam it sure would be worth a try.

Last summer when I took it into the dealer for an oil change, I complained about the initial idle being rough just after starting. It was better after using fuel injector cleaner and cleaning out the VANOS solenoids but still just not quite perfect. They came back to me and said that the ECU needed reprogramming. (I was convinced in my mind that the Mass Airflow Sensor was bad; but they said it was ok because it showed no codes). So I let them do the reprogramming. About a month after the reprogramming the idle just after start was still not quite perfect so I called the dealer and made an appointment to see them the next morning. I unplugged the MAF and started the car and the idle was perfect, so I was going to press hard to get them to change out the MAF. I have an extended warranty. I plugged the MAF back in and went to bed. Well, the next morning I start the car and the idle was perfect. I shut it down and waited a few minutes and restarted. Again, perfect idle. I called the dealer and cancelled the appointment. I figured a visit would be a waste of time if the car is behaving perfectly. That was last August and the idle is still rock solid perfect on every start.

I too experienced this in my 2000 M Roadster at about 30K miles shortly after I purchased it . Put in new Iridium spark plugs and the problem disappeared. Also noticed a slight uptick in throttle response at tip-in of the throttle. Also ran injector cleaner through a couple of tankfuls of gas, but I think the plugs did the trick.