Idle drops by a few hundred RPM's. Checklist.

[CoconutPete]

This is the 2.8.

When the car sits at idle, the RPM's will drop a few hundred for about 1 - 1.5 seconds. Then bounce back up to normal.

I pulled it apart and found a tear in the lower intake boot which I replaced.
I also thoroughly cleaned the ICV which had a LOT of buildup in it.
I cleaned the CVV just for the hell of it, not sure if it did anything.

Put it all back together last night and things were completely unchanged.

Any suggestions as to what's next on the list of "usual suspects?" Clean the MAF? Air filter is new and the enclosure is clean.

She pulls great and is torquey at speed. Really, the engine purrs - it's just this interesting little fluke at idle.

[s8ilver]

Rebuild your VANOS. One way to confirm is to unplug the connection to the VANOS. If your idle dip goes away, your seals are bad.

http://www.beisansystems.com/procedu..._procedure.htm

I have the same idle dip when cold. I have the seals, just not the time at the moment.

[CoconutPete]

Interesting thought. I hadn't given it any thought due to not experiencing loss of torque or the bogging/surging at 3K. I also felt the power distribution is smooth.

I'll give the "unplug test" a try though.

[cushjbc]

I hadn't given it any thought due to not experiencing loss of torque or the bogging/surging at 3K

I had the same doubt about this; had a barely noticeable step in power at around 3000RPM - I did the Beisan seals and anti rattle kit last weekend and was surprised to find how much torque I was missing below 3000. Delivery was quick, instructions are good, results are impressive.

Honestly, it feels like this engine woke up from hibernation.

[s8ilver]

I think it's due to the gradual degradation. The loss is very incremental I imagine as the seals go south.

I need warmer temps and time to do mine, but excited to get back any power lost. Can't hurt, and what's it cost, maybe $120 if you do it yourself and replace VCG and a few other bits while you're at it?

[ihm96]

I'm in the same boat. I've done smoke tests, changed the MAF, etc but I'm fairly certain its the vanos seals, I just haven't had time ever since I put my E34 over a curb and forced the Z3 into daily duty

Rebuild your VANOS. One way to confirm is to unplug the connection to the VANOS. If your idle dip goes away, your seals are bad.

http://www.beisansystems.com/procedu..._procedure.htm

I have the same idle dip when cold. I have the seals, just not the time at the moment.

[CoconutPete]

All good points. At 18 years old and 145K miles, perhaps it's time not matter what.

PO loved FCP Euro and AutohausAZ......

Valve cover gasket and radiator hoses were un-opened in a box in the trunk when I bought it. I smell a day off when it gets a tad warmer....

[me77]

+1 for the Beisan seal kit. Don't go with the other brands, his is the real deal.

Be sure to also get those little valve cover rubber grommets that are not included in many valve cover gasket kits. If you reuse the old ones, it'll still leak but in different spots (don't ask me how I know).

https://www.fcpeuro.com/products/bmw...er-11121437395

Count on your current VC how many you need, if I remember correctly you need 15.

[Tim95M3]

I had the same problem with my TUB28, rebuilt the VANOS and it solved the problem.

[FINZ]

I had what sounds the same issue with my S52. At idle rpms would drop dramatically then go back up. It ended up being the throttle position sensor. Replacement solved the problem.

[CoconutPete]

I had what sounds the same issue with my S52. At idle rpms would drop dramatically then go back up. It ended up being the throttle position sensor. Replacement solved the problem.

Did your car throw a code for this? Mine is not throwing any codes.

[s8ilver]

Did your car throw a code for this? Mine is not throwing any codes.

VANOS issue throws no codes to my knowledge. Have you unplugged the VANOS solenoid to see if the dip goes away? If it does, it's absolutely your VANOS seals. I started at the ICV just like you did. Mine was frozen solid. I cleaned it with carb cleaner to get the rattle back (the rattle should occur) with zero change in idle.

My issue does go away when the temp needle reaches the middle of the gauge, but I'm sure I'm still down on power.

[FINZ]

Did your car throw a code for this? Mine is not throwing any codes.

Only threw a code at the very end, as I was driving to the shop to do a "just replace the darned sensor, nothing else has worked, and I saw someone on BimmerFest forum solve it this way" That was in 2005 or 6. Before that no codes. The code it threw was - throttle position sensor.

[sjfuqua]

Experiencing similar symptoms with my 2000 Z3 2.8.

Looking to do the troubleshooting suggested to unplug the connection to the vanos and see if the problem goes away.

From the rebuild procedure at the above link, looks like there are several connections to the vanos, and looking at the Z3 nothing is jumping out at me as the connector.

Can someone provide a little help -- where is the connector(s) that should be unplugged for the vanos to verify the symptom?

Thanks.