Hi All,

You may have seen my thread recently on the SAI error code. Bit of background - since buying the car (4 months or so) cold start has always seemed a bit erratic/lumpy. As the weather got colder the symptoms got worse. After fixing the SAI the idling issues have most definitely increased further.

On start-up the car idles high, sounding a bit lumpy. Then when it tries to settle the car rocks and struggles to hold smooth, it sounds like its missing, infact it sounds like it will stall out (but never does). This continues for a good few minutes. If I drive the car it dips in revs and bucks on occasion, acceleration remains unsmooth for a minute or so of driving but as the coolant temp starts to rise the car settles and drives fine, smooth idle etc...

Once warm all symptoms dissipate and the car runs fine.

I have no CEL, no error codes logged. Does anyone have any suggestions on what could be causing this? MAF? coil packs? I have a Durametric, any ideas on what values I should try logging?

Thanks for any help
James

 

sounds fuel related though when my pump went. it just *went*.. and then plugs/coils/maf is the next thing i'd be looking for.. my car will "buck" ( but not as dramatically(?) when the maf is failing but yours sounds more like a fuel issue(?) clogged injectors failing pump!? GL w it.

 

thanks for the reply, I did wonder about a leaky injector. Will attempt a MAF/coil replacement and TB clean and go from there.

 

i noticed you said you had a durametric.. but no codes? i would be careful with the idea of throwing parts at it.. unless you can/do DIY? ( since plugs/coils are *relatively* easy and cheap for someone who does diy ) but absent that, i would get a proper diagnosis before i bought anything. unless the foregoing applies. again.. GL.

..and yeah.. fuel or spark related.. i would guess(?). i don't think the tb acting up would cause the bucking.. more like fluctuations in idle or decel..not responsive enough etc., rather than a "starvation" kind of thing. that's what makes me suspect "fuel" related. hopefully someone that knows wtf they are truly talking about will chime in also.

 

I disagree with it being a fuel issue. It is possible something is loose that is allowing in air after the MAF. As metals heat up they expand and seal the opening much better. You may not necessarily get a code for this. Also consider a faulty coolant temperature sensor. Some cars have two, one for the gauge and one for the ECU. I don't know what this car has. I'm guessing the Durametric will give you the value of the sensor and you can check it against nominal. I have to get one of those Durametrics at some point.

 

bad mafs can certainly cause hesitations.. but also usually throw cels. but are you suggesting a faulty temp sensor gauge might/could cause bucking and hesitations? never heard that one before

 

Not the sensor for the gauge, the one for the ECU... assuming this car has two sensors. I don't have the service manual on this computer to see what this car has. I've had similar symptoms on other cars.

 

i did see for the first time that after the car warms up, he says it runs ok. i agree, it probably isn't fuel related. although a failing fuel pump has been known to mimic some of those symptoms. hesitation/bucking/stall/fail... and it CAN run fine..then badly..just before it dies.. just sayin'.


op.. pls post back what you find. ( ok, fellas.. side bets are on )

 

if you had checked all above.....test your fuel holding pressure at stand still....maybe you lose that pressure over night

 

This generally won't cause any issues for longer than a few seconds.

 

Thanks for all the input, Not had a chance to do much yet, I did plug the car into Durametric and run the individual cylinder misfire along with intake temp and actual temp.

When the car was started I saw a few sporadic misfires whilst it was on choke for a minute or so. As it tried to settle into a warm idle (where it sounds like it will stall) I counted 10+ in cylinders 1 & 4 and 1 in cylinder 5, this was all in the space of 10-15secs. Once the car was up to temp no further misfires were detected.

As for intake temp this sat about 5 degrees above external temp (which seems acceptable?), I did at one point see it register -48c but this was momentary and may have been due to the old software version I was using.

I'm hoping this points to cracked coils warming/drying out in the problematic cylinders? time to upgrade to the 997 variety?

I did notice the car will only display 0.7 bar max boost, is this normal for an x50? I'm sure when I bought the car I saw 0.8 most of the time and even 0.9 on occasion

a reply to a few questions:

02996ttx50 - I am a bit of a DIYer so hope to carry out fixes where I can. I may have been a bit over the top when I said 'bucking', its more like trailing throttle is not smooth, the car tends to buck a bit as if I'm altering pedal movement.

sinking - Someone else on the UK forum mentioned coolant temp, I will try logging this and post results

 

then i would go straight to coils and the 997's are right...
and yes, depending upon ambient outdoor temps you should see occasional spikes of .9's on an unflashed x50 car but .8 and sustained regularly. but .7 may just have meant you didn't make proper boost then, that particular time..? coils.. plugs.. i think you're getting to it.. one of the proper tuner pros will hopefully add to the guessing ( but it's not for you, of course ) *game*.

coolant temp again huh.. sure wish i knew wth that meant..

 

What was your MAF voltage on your Durametric readings?

 

It may or may not be the case for this vehicle but at least in others coolant temperature is one of many parameters used to determine timing and fuel. If the sensor for coolant temperature is feeding the ecu bogus data then the timing and fuel won't be right. Garbage in/garbage out. CTS is basically a thermistor. (again, could be different on this car. I was just throwing out things to look into that should be easy to rule out with a Durametric.) It should change resistance with temperature. If for some reason it doesn't change resistance then it will feed reasonable data when the engine is in one temperature range and bad data when in another.

Make sense?

BTW, I see you're in LA. I was just traveling south to LAX this morning and saw several small convoys of 911's traveling North away from LA. Was something going on or is that normal?

 

it does, thx for the clarification.. you had me at thermistor

..and yeah.. cadre of 911's in la is normal everyday..lol but heading north? maybe the first mass evacuation of smart guys getting out while they can? kidding aside, sounds like normal sunday la stuff. you have to drive north to be able to really *drive*. eg,.. i myself had a 997.1t for early breakfast today

apology to the op...and pls post your findings.