1990 316i (M40B16) idle vibration

[omera60]

Hello,

I have a 01/1990 316i Automatic Saloon Non-KAT (leaded fuel equipment) VIN: AB78104. I have some issues that I would like to ask you guys/gals. When I first start it in the morning, the first throttle press I do results in a jerk/hesitation, unless I let it idle for some time (5mins+). When the engine is cold if I come to a halt there is a vibration throughout the car. The rpm's are stable no jumping etc. Once the engine is up to its operating temperature the vibration lessens but again if I come to a halt it can be felt through the spine or holding the steering wheel, but this time it comes and goes, like a wave effect, even if I put the trans to park It can be felt, not as bad as in gear but nevertheless. There is no problem the vehicle is in motion, it is babyface smooth, this only happens in idle. If there is any electrical load on the engine (external lights etc) the vibration will get worse. The things that I did are as follows, bear in mind all these parts came directly from BMW Classic so all of them are OEM except the exhaust.

-Timing belt change
-Engine-Tranny mount change
-Brand new AFM
-New High Power spark plugs
-New fuel filter
-All new fuel lines
-All new oil return lines
-Cleaned injectors
-Changed both blue and brown coolant temperature sensors
-Brand new radiator
-Ran smoke test, no leaks from it
-Brand new coil
-Brand new battery
-Brand new ICV
-Checked TPS
-Brand new fuel pump
-Brand new distributor cap and parts
-A brand new crank position sensor
-Refurbished alternator
-Checked DME fault memory, nothing stored
-Checked idle speed via diagnostic, steady 800 rpm when not in gear
-Brand new DME and Fuel Pump Relays
-New Exhaust

These are the things that I remember doing. What maybe the cause of this issue? Do I have to live like this as it is normal or is there something I am missing? You guys are my only hope...

Best,
Omer

[roguetoaster]

So, that sounds more like a torque converter being balky, maybe another transmission component. Also worth it to check engine/trans mounts, flex disc, center bearing, diff bushing.

[omera60]

So, that sounds more like a torque converter being balky, maybe another transmission component. Also worth it to check engine/trans mounts, flex disc, center bearing, diff bushing.

I will check all of these. I got the engine and tranny mounts about 2 years ago. What is your opinion on the exhaust though? Could it be the culprit? The issue is apparent when idling in gear so I don't think it can be caused by anything beyond the transmission as nothing else moves beyond that when idling?

[roguetoaster]

Can't think of how the exhaust would cause an issue when cold, and then again at warm idle, but not while running otherwise.

On rereading I see that I missed electrical load worsening the issue, maybe you should also check the resistance on the spark plug leads, and just to be safe, check alternator output at different RPM ranges/verify that the alt is mounted solidly/recheck belt tension.

[omera60]

Can't think of how the exhaust would cause an issue when cold, and then again at warm idle, but not while running otherwise.

On rereading I see that I missed electrical load worsening the issue, maybe you should also check the resistance on the spark plug leads, and just to be safe, check alternator output at different RPM ranges/verify that the alt is mounted solidly/recheck belt tension.

Exhaust didn’t sound plausible to me as well, it was suggested that it might cause problems because it’s not OEM but it is in stock form not cut, open or etc, someone suggested it but I don’t see the relation either. Just this morning I found and bought a OEM NOS spark plug wire set from eBay, in the meantime I’ll check the resistance on those that I have. Do you happen to have the correct values for the resistance?

[omera60]

So got an update, the other day I made a small day journey to a another city near Istanbul. On the highway I noticed the following; around 120-140kph indicated and engine around 3-4K rpm if I lift off my feet from the throttle (not fully) I get a vibration noise. I had a friend on the front passenger side and he told me it is concentrated around the rear seat behind the driver. If I press or fully lift from the throttle the noise/vibration goes. It sounds like it is coming from the exhaust but what causes it is a mystery.

[roguetoaster]

Could be an exhaust shield.

[omera60]

Could be an exhaust shield.

I inspected the heat shield, it seems intact. Raised the car with my mechanic. Juggled the exhaust, no noise. Ran the car in gear still no noise. I think it needs to be done on the road. Also he told me that there is a sound coming from the exhaust but it’s due to mixture in the engine. He said I should get my 4 gasses measured to see. I got them checked, they indicated it was running lean, thus giving a low rpm. I also bought 4 new injector and replaced them to give ease to my mind as the ones I had on was the original ones (30 years old, didn’t throw them away, cleaned and packed them for future). He suspects there is a vacuum leak somewhere. I have done multiple smoke tests before with all negative outcomes. If I open the oil filling cap when running, the engine surges, if I pull the dipstick there is not change the way it runs. Do you have any idea for where the leak might be?

[omera60]

Just to bump this up again. What may be the reason for steady but low idle rpm ( maybe between 600-700 whereas it should be 800 +/-40)?

[omera60]

I wanted to help anyone who might have the same problem now or might down the road. Both the throttle’s stop screw and CO poti on AFM was in need of adjustment. BMW recommends (for my vehicle, it changes with sub versions) %0,5-%1,5 . Currently I set it to %0,7 but will increase it to %1,0 to stabilize the engine. When I measured the CO before the adjustment it was %0,04! Also the sound turned out to be coming from the differential. The pinion bearing was worn out, it has been changed and I will pick the car up today.

[AA_318iA]

Well i'm kinda having the same issues on cold start, i ve 318i A. When i start the engine rpm sits on 700rpm but if i put gear on drive it just go down to 200 then turn up to 500 n stalls. I have to wait for temperature to go up to blue so then i can drive... So did you fix the issue on your car? Thnx