Temporary rough idle

F

flybobbie

Lifer
 Stourbridge
Something my car has been doing for some time is the rpm fluctuates on start up.
Goes to fast idle 1200rpm, then drops back to 600 then back up to 1200 a few times, totally random, then settles.
Having fitted a voltmeter i see the voltage showing 12.2, 11.5 after start then takes about 4-5 seconds for alternator to kick in, to hit 14.5-14.7 volts.
Then idle stabilizes when volts are 14 plus.
Drives fine after that. Just wobbly until alternator kicks in.

No other weird things happening.

Any ideas?

Got to admit my car is still on call back for power connector problem, perhaps i should get it done.
 
flybobbie said:
Got to admit my car is still on call back for power connector problem, perhaps i should get it done.
Click to expand...

That would be my first port of call and maybe tell them about the issue you are having at the same time .
 
The only think i associate with the idle problem time wise, have been using my heated seat mod a lot wired to the cigar socket wires.
I wonder if the battery is not being fully charged, starts ok. I might drop it on a battery charger and see what happens and run the car with all ancillaries off for a while..
 
Have you tried starting it from cold with the maf disconnected? I think the dwell time before the battery voltage rises is a normal thing, mine does the same - i put it down to power hungry things like heated lambda sensors, air pump etc being fired up from cold. I do have a stable idle though.
Rob
 
Could try that.
Tomorrow might just pull battery and give it a good charge. Don' have means to charge directly via bonnet terminals.
Problem these days journey to work only 15 miles return, so 2 20 minute journeys.
I use to do a 30 mile return journey weekly that probably gave a better charge.

Last time battery was removed i lost all the names of music in memory.
So i think it would be ok to drop a 12volt battery on the terminals under bonnet to keep the memory whilst boot battery is out..
 
Check your eccentric shaft sensor for leaks. Pull the connector and look for an oil leak.
 
Well put my Foxwell reader on today, check the battery status, it shows historical capacity data.
Today 61% last few days it dropped to 57%, averaging 60%.
It also shows how many hours the battery has been at different %.
Most hours at 80%, but lots of much lower readings.

So why not 90 or even 100%.
60% seems low.

I put my charger on the removed battery.
Although charger says not agm.
Tried anyway, initial volts was 12.1 now says fully charged 14 volts on multimeter..

I can't believe 40 minutes as charged up the missing 40%.

Well would seem i can use a std. charger, just have to monitor the voltage, not let it go beyond 14.8.
Seems i can let it sit for 4 hours, but watch the voltage.
 
Well had to go back and check when i first fixed the broken wires in the boot draw motors.
Can't believe that was back in 2016.
I replaced the battery thinking it was a battery problem as it was the original 2009 battery.
So the battery is nearly 6 years old.

Looks like i might be needing a new battery if it's only holding 60% capacity.

Seen some videos reviving old batteries using welding sets :evil: .
 
flybobbie said:
Something my car has been doing for some time is the rpm fluctuates on start up.
Goes to fast idle 1200rpm, then drops back to 600 then back up to 1200 a few times, totally random, then settles.
Having fitted a voltmeter i see the voltage showing 12.2, 11.5 after start then takes about 4-5 seconds for alternator to kick in, to hit 14.5-14.7 volts.
Then idle stabilizes when volts are 14 plus.
Drives fine after that. Just wobbly until alternator kicks in.

No other weird things happening.

Any ideas?

Got to admit my car is still on call back for power connector problem, perhaps i should get it done.
Click to expand...
WHich Zed do you have??
 
23i.
Seems to run ok now the battery has been charged.
I will give it a week and do the capacity check again.
I can see why now the battery needs registering when replaced.
I assume it zeros the capacity and hour usage in the memory.

So roughly last 6 years since replacement is 6yrs x 365days x 24 hours = 52,500 hours of use.

I noticed one readout said battery was 70 to 80% capacity for 11,000 hours.
As well as various break down of percent was shown either side of that, but can't recall what.

If i re-register this old battery i guess all this information would be zeroed.
 
So battery all charged up (now showing 90%), still slight wobbly idle.

But now noticed i need to push down on the brake pedal a lot more to get good brake effect, as i found out as i rounded a bend to find a post office van pulling out. Brakes were all soft, needed a good push. Not like that before.
First thought was replace fluid and bleed.

I wonder if i have a vacuum leak.

I assume the 23i takes it's vacuum from the manifold. Not a pump like turbos. Am i right?
If i push down on the brake pedal it very slowly goes all the way to the stop. Even if pumped a few times.
I'm sure it should go rock hard after a few pushes.

Could this be the old BMW plastics giving out somewhere?
 
flybobbie said:
So battery all charged up (now showing 90%), still slight wobbly idle.

But now noticed i need to push down on the brake pedal a lot more to get good brake effect, as i found out as i rounded a bend to find a post office van pulling out. Brakes were all soft, needed a good push. Not like that before.
First thought was replace fluid and bleed.

I wonder if i have a vacuum leak.

I assume the 23i takes it's vacuum from the manifold. Not a pump like turbos. Am i right?
If i push down on the brake pedal it very slowly goes all the way to the stop. Even if pumped a few times.
I'm sure it should go rock hard after a few pushes.

Could this be the old BMW plastics giving out somewhere?
Click to expand...

It could be the master cylinder seals wearing out? But an air leak would fit in better with your lumpy running :?
Rob
 
flybobbie said:
That is what i am thinking.
Looks like a a smoke machine or cigar testing job.
Click to expand...

If you’ve got the right diagnostic kit you could check the fuel trims to see if the car’s been adding extra fuel to compensate for an air leak.
Rob
 
Looks like it is fitted with a vacuum pump.
https://www.realoem.com/bmw/enUS/showparts?id=LM32-EUR-05-2009-E89-BMW-Z4_23i&diagId=11_3758
 
Again, have you checked the plug to the eccentric sensor? Is it leaking?
 

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