BMW M5 Forum and M6 Forums banner

1 - 19 of 19 Posts

·
Registered
Joined
·
209 Posts
Discussion Starter #1
2001 model 90,000KM's on it.

Car is quite jerky in the throttle during the first 2-3 minutes of driving. While hold your foot steady cruising down a side road the car shudders as it goes down the road, like the throttle is being moved around very slightly. Once warmed up it is smooth and there is no issue in this regard.

MAF's are brand new Bosch units (less than 10,000 km on them, installed last fall).

No CEL, I have a peake but last time I scanned there were no codes.

Any suggestions on where to start with this?
 

·
Registered
Joined
·
991 Posts
2001 model 90,000KM's on it.

Car is quite jerky in the throttle during the first 2-3 minutes of driving. While hold your foot steady cruising down a side road the car shudders as it goes down the road, like the throttle is being moved around very slightly. Once warmed up it is smooth and there is no issue in this regard.

MAF's are brand new Bosch units (less than 10,000 km on them, installed last fall).

No CEL, I have a peake but last time I scanned there were no codes.

Any suggestions on where to start with this?
Mine does the same. Im thinking the SAS is the culprit, as it is running during initial start up. I think it messes with the O2 sensors or maybe the MAFs and makes the car all lurchy. Give it 60-90 seconds before driving, or listen for the pump to cut out, and you should be good. Just how these cars are...
 

·
Registered
Joined
·
2,586 Posts
Some things that come to mind: plugs...coils...fuel pump...vacuum leak.
 

·
Registered
Joined
·
355 Posts
I find my throttle is less punchy in sport mode during first minute or so of warmup in the mornings.
There are lots of threads about punchy throttle when cold; I don't even notice anymore. Being extra ginger on the throttle in the mornings is just part of learning how to drive the beast, IMHO.
 

·
Registered
Joined
·
36 Posts
The reason it's jerky is that you might be in too low rpm (upper gear) and you have to release the clutch differently when cold or it will have jumping effect. Let the car warm up for a minute too.
 

·
Registered
Joined
·
4,488 Posts
Mine has this issue too. It smooths out as soon as the SAP turns off. I've logged a lot of things to see what might cause this, like fuel trims, O2 sensor readings, MAF reading, ignition timing, VANOS angles, injection times, and the only thing that changes significantly when the SAP turns off is the O2 sensor readings, which are both stuck lean at 0.000V while the SAP is running and jump to steady rich at about 0.85V when the SAP turns off. But that's to be expected since that SAP is pumping all kinds of oxygen into the exhaust when it's running, and the AFR goes rich after SAP shutdown because the DME is still in warm-up enrichment mode. The DME is ignoring the O2 sensor readings anyway when the engine is cold.

These cars couldn't have been like this when new so something has degraded with age to cause this, but I've no idea what. I just live with it.

I have a Jailbreak tune now but it was like this with the stock tune. I should ask Jailbreak if they can fix this.
 

·
Registered
Joined
·
71 Posts
I also have this issue, mostly just after the time the SAP goes off so perhaps is related to where it goes into closed loop mode (or just happens at that part of the warming cycle). I notice it more if the previous journey was long on fast roads which makes me think the adaptions start to settle to run well when hot on the fast roads and then aren't quite right for a cold start. It was very obvious after I last reset the adaptions and improved steadily as one would expect but has never quite got it right under all conditions which does suggest something is getting out of spec. I also wonder if it is related to vanos adaptions or response times rather than fuel trims. I have run vanos tests every 6 months and they always pass with decent margin but those tests have to be done with the engine (and oil) hot. I suppose cold oil could slow the response of the vanos system and put it out of spec for the adaptions it has settled on. I'm not sure what adaption parameters the dme takes into account for the vanos system but if leakage and reaction times vary significantly from hot to cold running then the adaptions may not "keep up" with it.

I don't worry about it too much. I remember how my old V8 Landrover drove when warming up :eek:. Big engines with more torque seem to make small running issues a lot more obvious.
 

·
Registered
Joined
·
4,488 Posts
It occurs to me that one thing does happen when the SAP shuts off. Immediately after a cold start, the exhaust cam timing is retarded by 30 deg and it stays retarded during warm-up, which means the exhaust valves stay open well after TDC and some HC-rich exhaust gas gets sucked back into the cylinders. According to a google search, this is to "reburn" the exhaust-stream HC to reduce emissions.

While the SAP is running, the exhaust in the ports is being "aerated", so O2 is getting sucked back into the cylinders with the HC, leaning the mixture. When the SAP shuts down, the O2 feed into the ports stops.

Since the fuel mapping for smooth running in the SAP-ON mode would have been developed for unplugged SA nozzles in the exhaust ports, maybe the gradual plugging over the years degrades the SAP-ON mixture control. But then I would have expected complaints about poor cold running from owners of engines with completely plugged SA ports, and I don't recall that being the case.
 

·
Registered
Joined
·
1,024 Posts
Guys - here's another data point - as my car 'did' the same thing and now does not:

After a $340 tow from Truro Mass to Braintree Mass (Import Auto Werks) this past Monday due to a failed fuel pump (this is my 3rd pump at 260,000 miles), and after it's installation, the morning jerkiness is gone. As I recall over 12 years of ownership, the fuel filter also contributes to this phenomenon. (Alvin - thank you again !)

As with the last fuel pump installation, the increased power is AMAZING. It's clear that pumps, like anything else on this car degrades over time.

If you've not changed your fuel filter in the prior 25K, just do it - now, as the increase in power/ responsiveness is also immediately evident. The added benefit is less strain on your fuel pump...
If you've not changed your fuel pump and you're over 100K, just do it (and avoid the tow charge as they fail catastrophically).

Hope this helps

BTW; for those playing along, original clutch still remains :)
 

·
Registered
Joined
·
77 Posts
I had this problem and it was bad. I mean really bad. I did some preventative maintenance changing all O2's and all cam position sensors. After this the car did not exhibit this problem. I just installed the Evolve Alpha N tune and the problem is completely gone and the car runs amazing. I have 65k on the odometer.
 

·
Registered
Joined
·
300 Posts
Guys - here's another data point - as my car 'did' the same thing and now does not:

After a $340 tow from Truro Mass to Braintree Mass (Import Auto Werks) this past Monday due to a failed fuel pump (this is my 3rd pump at 260,000 miles), and after it's installation, the morning jerkiness is gone. As I recall over 12 years of ownership, the fuel filter also contributes to this phenomenon. (Alvin - thank you again !)

As with the last fuel pump installation, the increased power is AMAZING. It's clear that pumps, like anything else on this car degrades over time.

If you've not changed your fuel filter in the prior 25K, just do it - now, as the increase in power/ responsiveness is also immediately evident. The added benefit is less strain on your fuel pump...
If you've not changed your fuel pump and you're over 100K, just do it (and avoid the tow charge as they fail catastrophically).

Hope this helps

BTW; for those playing along, original clutch still remains :)
Vics,

How did you like Import Auto.... I've heard great things about them and esp Alvin... I've heard he's an E39 specialist among other things.

- MIke
 

·
Registered
Joined
·
10,114 Posts
What he said.
Age will get the parts in the Vanos more than miles. Solder joints, rubber orings, and a filter that breaks down from the oil. All those things are age. Less miles would mean you are more likely to have the solenoids with crap from the filter stuck in them. More miles is more oil pumped through with a likely result of some cleaning.
 

·
Registered
Joined
·
1,024 Posts
M
Vics,

How did you like Import Auto.... I've heard great things about them and esp Alvin... I've heard he's an E39 specialist among other things.

- MIke
Hey Mike - Alvin's awesome - BMW certified - M knowledge's fantastic and who has an 11 year old M5 specific fuel pump in stock? I was w/o car for less than 24 hours - PM me if you require additional input - cheers
 

·
Registered
Joined
·
427 Posts
I have the same jerkyness on start up. But after a few minutes it's all good.
I think my car could use some basic maintenance though.
 
1 - 19 of 19 Posts
Top