HELP!!! 1yo issue still can't fix
 

Hello,
I have 2013 US Spec MCS R56 Manual with 90K miles. N18

The car used to run perfectly, almost one year ago in the morning, it suddenly started running rough and revs started to fluctuate at every Cold Start since than. after it gets little warmer(after 2-3 min of idle) the engine runs perfectly.

Did a Lot of Investigation but found NOTHING.

NO CEL. (noticed that once per 3-4 month P0136 comes randomly but doesn't come back any soon after I delete it.)

Replaced MAF, thermostat, Upper O2 sensor, Spark Plugs, Coils, HPFP all of this parts for ZERO result.

checked for compression on cold and on warm engine - 13-14 Bar among all 4 cylinders.

checked for boost/vac Leak - nothing.

removed and cleaned Vanos solenoids.


I also Noticed that car runs worse when its getting colder outside.

Still Cant find anything.

p.s. Once its warm it Car runs Great. Made 180 WHP baseline on 91 with just Wagner IC, NM intake piping and NM intake, no tune.


PLEASE Give me ANY advice, I'm getting frustrated.
I Really love that car and its very painful for me watching it idle like a crap every morning.

will add youtube link of a coldstart soon.

Have you watched fuel pressure on cold start? Should be between 700-800psi (48-55bar) at idle.

hey there,
thank you for replying.

Checked Fuel pressure this morning, it was around 1000-1050 PSI - 68-72BAR - do you think im getting TOO MUCH fuel pressure ?

I will recheck fuel pressure later today.

(p.s. I have replaced HPFP before but got ZERO changes. btw I have later model, revised HPFP which is not prone to failing )

Still Got Nothing.
Please Help :(

*dead Inside*
help

The short term fuel trim is pinned at -25% which means it’s pulling a lot of fuel out. Is the car ever hard to start? Like cranks and cranks then finally turns over? Could be leaky injector that only effects the car when cold starting it.

Hello.

No it starts right away.

I have already done Injector testing about a week ago. they are perfect.

After all this investigation, I Still got no Clue.

i have a similar issue without any fix on sight. -19% long term fuel trim, hiccups only at cold start and low throttle input and low rpm situations. other than that idle is rock smooth even on cold start. fuel trim eases to about -16% if i drive slowly.

if you fix your problem, please let me know.

add me to the list, once temperatures are in 50's, I have jerky, laggy throttle first 1-2 minutes of driving. Once engine warms up - no issues, everything is awesome.

Was shooting parts cannon at the car: got new MAF, OEM coils and spark plugs, new injectors, high and low pressure fuel pumps, fuel filter, cleaned carbon build up, new thermostat, water pump, pulleys, belt, valve cover and timing chain guides. 2011 early build N18 with 138k miles.

can you also check your fuel trims?

Small update for those who interested: i picked a cheap noisemaker delete rubber hose from aliexpress and bolted it in. Fuel trims are still the same but there is noticeably less jerkyness now.

Cold start throttle lag is still there but it’s more subtle.