Occasional stutter when warm?

[me77]

I have a '99 Z3 2.3 5MT that recently developed a little issue: After the car has been driven for 20-30min., it will often (but not always) stutter a little bit when accelerating normally from a stop. When accelerating very cautiously, it is barely noticeable. The stutter only appears in the lower RPM regions and it happens with AC on or off. There are no issues at speed or when the car is cold or not fully warmed up. The Check Engine light is off and there are no saved or pending codes in the engine computer.

It has 89k miles, I have no service history for the car except that I replaced the thermostat two months ago. Car runs fine as far as I can tell (except for the mentioned stutter) and gets decent MPG.

Any ideas? I thought about replacing the spark plugs, but I have the feeling that some electric component gets heatsoaked and cuts out once in a while. Ignition coils?

[Vintage42]

... '99 Z3 2.3 5MT... will often... stutter a little bit when accelerating... only appears in the lower RPM regions... has 89k miles, I have no service history for the car...

Some of the symptoms are similar to worn VANOS seals, but that should cause a code.
http://www.beisansystems.com

[me77]

I thought VANOS issues almost only appear when cold? At least that‘s what I‘ve read often. It idles good, cold and fully warm. I have none of the issues listed on the Beisan website.

[LannVouivre]

Check spark plugs for wear. They're nice and easy on these cars, hardest part is getting the decorative cover's bolt covers off.

[s8ilver]

I thought VANOS issues almost only appear when cold? At least that‘s what I‘ve read often. It idles good, cold and fully warm. I have none of the issues listed on the Beisan website.

I 2nd this. I have a stutter from about 1/4-1/2 on temp gauge...vanishes when fully warmed up. If I unplug the VANOS the stutter vanishes. I bought the seals and I'll get to them someday.

I would start with plugs and go from there. Perhaps toss in a new fuel filter for peace of mind, and maybe inspect injectors. I wouldn't suspect them at 89k, but who knows. I bought a rebuilt set that I'll throw in next time I do plugs.

[gmushial]

Also with a '99 2.5L 5sp (220k mi) ... when cold there would be a rough idle; but the low rpm stumble, and general gutlessness was at any/all temps... replacing the seals was one of the best "mods" I did [a 5hr $40 job[] - the before and after were like two different cars. :-) ... you can check all the other likely suspects, but if it's the VANOS seals, it will only get worse, to the point of trying to start up smoothly from a stop sign becomes a challenge; trying to do such on an uphill: almost impossible.

[s8ilver]

My seals aren't that bad yet, but I know I need to do them. 5 hours seems reasonable. I'm at 148k miles and no history on the seals. My stutter only developed in the last 1.5k miles or so.

I have a fresh tune to try but told myself I can't install it until I do the VANOS seals.

[gmushial]

My seals aren't that bad yet, but I know I need to do them. 5 hours seems reasonable. I'm at 148k miles and no history on the seals. My stutter only developed in the last 1.5k miles or so.

I have a fresh tune to try but told myself I can't install it until I do the VANOS seals.

If I remember, I did my seals around the 140-145k mark... and like you, the gutlessness appeared over a relatively short time: went from didn't notice anything, to: if this continue to get worse at this rate, this is going to be undriveable in no time... and at that time I wasn't sure what was wrong - was afraid that I was losing the engine: values, or rings, or ???... so was very grateful when it proved to be the seals...

W/re the new tune: don't even bother until you do the seals.

[Tim95M3]

Definitely aged/worn spark plugs. I have the same issue with my roadster.

[gmushial]

Definitely aged/worn spark plugs. I have the same issue with my roadster.

I don't know about definitely, but it would sweet it that's what it was... ;-)

[rboehl]

I had this with my Roadie and ir ended up being a coil going bad. It completely failed one day a couple of miles from home and I limped in and read the codes. Replaced all of the clips and plugs and 7 k later all is still ok.

[LannVouivre]

Pull a plug and look. It'll take like 5 min and then you get to rub it in our faces when we're all wrong! Fun!!!

[me77]

I‘ll replace the spark plugs soon, will report back if that cured it.

[LannVouivre]

I want pictures. I just did mine today, they were little smooth nubs. Of course, I'm lying in bed so I'll have to settle for being a hypocrite until tomorrow.

[me77]

So I put new spark plugs in it (NGK 7092, BKR6EGP) and so far I would say that this fixed the issue. It starts a little quicker, it feels more responsive in the lower RPM range and I couldn't get it to stutter anymore. The plugs that I took out were most likely the original ones it left the factory with (ceramic insulator has "NGK BMW" on it), here is a picture of one of them. They all looked identical and had around 90100 miles on them.

IMG_0567edit.png

Sorry for responding so late, I kind of forgot about it.

[LannVouivre]

I also forgot. I was going to pop in and suggest a speech therapist.

Also, those plugs are SO worn. You'd be hard pressed to replace those and not have a huge improvement.