Cold start issues - Lumpy idle bucking, trying to stall

[shantybeater]

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 problem has increased or is at at least prolonged

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

 

[Mac996t]

Have you been able to compare your car starting, with another, to rule out a case of they "all do that sir!" ,my car has a busy idle when first started, it's note changes constantly and it takes a minute or so to settle to a smooth idle.Mine doesn't do the rev dipping thing you mention though and drives smoothly.

I have a Durametric and I know you can select a missfire counter for each cylinder. It might be worth checking them out to see if they are picking anything up.

I would also want to check the engine coolant temp is reading correctly as shown on the Durametric (not the temp gauge) to make sure the ECU is seeing the correct temp.

Something else worth checking is the reading from the MAF both when first started and with a warm tickover.

Another posibility is the throttle body may benefit from a clean, its the throttle body that adjusts the air flow to maintain the desired idle speed, but I would have thought a problem here would result in jerky running when warm aswell.

And finally it could be a leak on one of the many pipes.

Also if you want to compare your readings with my car I'm happy to oblige

let me know

Mac

 

[Mac996t]

Just thought, something else to check out are the small bore vac pipes on top of the engine, the reason is you know somebody has been messing around with your secondary air system, well the valves for this system are actuated by the engine vac so its possible this could have been messed with possibly leaving an open end or something.

Also do you have any history showing the maf being changed, if not it maybe a good idea to just replace it now, to rule it out and future proof it. I consider the maf to be a service item . PS do you have an aftermarket air filter that may could have contaminated the maf?

PS i take it you know the plugs are good and you've not been getting any missfires at other times?

Mac

 

[infrasilver]

I have a Durametric and I know you can select a missfire counter for each cylinder. It might be worth checking them out to see if they are picking anything up.Mac

Along with everything else Mac said I would also check for misfires through your Durametric live logging, you can check up to 8 things at a time so you'd be able to look at all 6 cylinders running.

 

[DeathStar]

Have you been able to compare your car starting, with another, to rule out a case of they "all do that sir!" ,my car has a busy idle when first started, it's note changes constantly and it takes a minute or so to settle to a smooth idle.Mine doesn't do the rev dipping thing you mention though and drives smoothly.

I have a Durametric and I know you can select a missfire counter for each cylinder. It might be worth checking them out to see if they are picking anything up.

I would also want to check the engine coolant temp is reading correctly as shown on the Durametric (not the temp gauge) to make sure the ECU is seeing the correct temp.

Something else worth checking is the reading from the MAF both when first started and with a warm tickover.

Another posibility is the throttle body may benefit from a clean, its the throttle body that adjusts the air flow to maintain the desired idle speed, but I would have thought a problem here would result in jerky running when warm aswell.

And finally it could be a leak on one of the many pipes.

Also if you want to compare your readings with my car I'm happy to oblige

let me know

Mac

+1 :thumb:

 

[shantybeater]

Thanks for the replies, especially Mac for making such a detailed reply.

I have no other car to compare to, started her at lunch today (8 degrees) and it idled ok but still missed a few times, will get Durametric connected and do the logs you suggested, will post back with values etc.. I assume if one or two cylinders keep missing it most likely points to crack coils?

I did also consider a TB clean and MAF disconnect, this will be my next step. I had a nosey around and couldn't see any loose VAC pipes, the SAI definitely appears to be working ok and no error codes have reappeared since the relay install.

As for history of MAF, I couldn't find any so it very well might be on the original. I assume design911 is the best bet for a replacement? (along with 997 coils). I have no aftermarket filter, this was also replaced in December on a major service, plugs were done near enough the same time and made no difference to the rough running.

 

[rottenbend]

Sounds very much like a vacuum leak to me.

 

[shantybeater]

Rottenbend - appreciate your input, I will cover leaks once I've ruled out MAF/TB/Coils. 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. (misread your reply MAC so will try coolant temp next)

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?

Also 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

 

[shantybeater]

Quick update - Cleaned MAF, removed Y pipe and Cleaned N75 with electrical cleaner. Also went at the throttle body although there was minimal dirt to be seen. I did see traces of oil in the Y pipe towards the F pipe, is this normal?

Unfortunately there was no change to the cold start, still lumpy and missing. I managed to see 0.8 bar on an empty carriageway this afternoon so ignore my previous comment.

Next up is coilpacks..

 

[shantybeater]

In an effort to keep the thread up to date I took the car out for a quick drive after work. Again a minute or so after start up as the warm idle tried to settle in the car began misfiring. I took a closer look at MAF readings which fluctuated constantly between 1.5 & 2.0v. This settled into a fairly constant 1.5v once warm at idle

Misfires showing:

I saw another 2 misfires in cylinder 6 over a period of 10 mins when fully up to temp, none on boost

Making up a shopping list of goodies to do along with the coilpacks (sparks, exhaust heatshields etc.)

Would anyone suggest replacing o2 Sensors whilst i'm in there or would that be overkill?

 

[infrasilver]

Just do the plugs/coils and see where you're at. No point wasting money on the O2 sensor if that's not the problem.

 

[Mac996t]

I've just tried the same tests as you and got pretty much the same result.

When first started there were no miss fires recorded and the maf voltage was mainly 1.9-2.0 but occasionally dropped to 1.8, then after about a minute and coinciding with the tick over dropping mine also started to sound lumpy and started to register miss fires on cylinder 4, the counter got to about 12 and there was also one ot two on a couple of other cylinders. The tick over didn't fluctuate though it just sounded lumpy for a bit.

After about 10 mins the temp gauge reached about 80'c and the maf voltage settled at about 1.4, changing between 1.35 and 1.45 which was about 23kg/hr

I wonder if the behaviour after a minute of running is when it starts using the lambda sensors because I know they have to be hot to give an accurate reading and most cars ignore them to start with?

My car has also had new 997 coil packs and standard plugs within the last 2k and the maf was new 7k ago.

I might watch another start and see what the lambda readings are up during the lumpy bit, I did check them after about 5 mins and they were both reading 1.00 so were controlling by then.

I also ran the car in my garage with the door closed and when I got out after 10 mins I could smell virtually nothing. If I run my bike with the door shut it stinks of fumes straight away, just shows how good the emmission control is on a Porsche LOL

Mac

 

[shantybeater]

Thanks Mac that is very helpful. Tomorrow I will run logs again and check to see if cylinder misfires coincide or not, will check lambda readings to match as well.

I have to say mine does smell quite strongly of fuel on initial startup which I figured is expected on choke. Wouldn't fancy my chances in the garage for 10mins!

We could do with a third person as reference, as you say it could just be before the o2's reach optimal temp?!