Part throttle hesitation and cold start stall
- Thread starter jcorallo
- Start date
Just out of interest, have you checked for air leaks, for example, at the air-oil-separator bellows?
I'm also told that early cars had trouble with bad seals on the engine oil filler cap, and also the fuel filler cap - both of which would allow air into the evap control system.
I'm going to check mine now - will report back.
Jules
I'm also told that early cars had trouble with bad seals on the engine oil filler cap, and also the fuel filler cap - both of which would allow air into the evap control system.
I'm going to check mine now - will report back.
Jules
Both caps appear fine and although i have not replaced manifold gaskets to ensure there is no air leak i have no other reason apart from this very cold start problem to suspect anything is amiss.
I have not checked the bellows (AOS) but i have no symptoms of a failed AOS -smoke / rough running etc.
After 30 seconds of starting my car is fine and it does only do this when very cold, normal overnight cold is no problem.
I can relate to the kangaroo syndrome, if very cold and i pull away the nose will dip as the revs drop then the pick up jerks the car again - very embarrasing so i just let it run for half a minute so i leave with some dignity.
Anyway, battery has been disconected and reconnected, run it for an hour or so for the ECU to relearn parametrics, so now i want a very cold day to test it.
Couldnt do the deal on the S today as the seller is sick so looks like i will continue with this thread, surely there must be more members who can offer some advice - what about Porsche mechanics - come on guys give us a hand.
This very definately a fault and not a characteristic, Im with Jules on this and we will crack it, i will replace whatever to sort this out even though my car is about to be traded in.
Glyn
I have not checked the bellows (AOS) but i have no symptoms of a failed AOS -smoke / rough running etc.
After 30 seconds of starting my car is fine and it does only do this when very cold, normal overnight cold is no problem.
I can relate to the kangaroo syndrome, if very cold and i pull away the nose will dip as the revs drop then the pick up jerks the car again - very embarrasing so i just let it run for half a minute so i leave with some dignity.
Anyway, battery has been disconected and reconnected, run it for an hour or so for the ECU to relearn parametrics, so now i want a very cold day to test it.
Couldnt do the deal on the S today as the seller is sick so looks like i will continue with this thread, surely there must be more members who can offer some advice - what about Porsche mechanics - come on guys give us a hand.
This very definately a fault and not a characteristic, Im with Jules on this and we will crack it, i will replace whatever to sort this out even though my car is about to be traded in.
Glyn
No mate, had a really cold night, started up, just opened the throttle to 1400RPM and hey, the drop came in again, i held the throttle as it was and the revs went up and down like a yoyo for about 20 seconds, then everything went fine.
I have changed so many things to sort this one little niggly problem, but no joy.
Anyway, saw another S for sale and today travelled 140 miles to go and see it.
One owner, Basalt Black completly unmarked - it looks brand new, its a 2002, with Hard Top, 18" GT3s, Litronics, park assist, coloured centre crests, PCM & Sat-Nav, phone, Black leather, cruise, Traction, PSM, Bose Hi-Fi with 6 CD changer, sports seats, Trip computer, Tracker, Approved Porsche Warranty, all three keys, service history, just had the 48000 mile service (£1500), Climate, and went like stink, i thought my 2.5 was pretty quick but this was mind blowing.
I cant believe my luck, Its better than sex (well it would be if i could remember what that was like)
£21000 but only gave me £9000 for mine as trade in, pick it up in two weeks,
Glyn
I have changed so many things to sort this one little niggly problem, but no joy.
Anyway, saw another S for sale and today travelled 140 miles to go and see it.
One owner, Basalt Black completly unmarked - it looks brand new, its a 2002, with Hard Top, 18" GT3s, Litronics, park assist, coloured centre crests, PCM & Sat-Nav, phone, Black leather, cruise, Traction, PSM, Bose Hi-Fi with 6 CD changer, sports seats, Trip computer, Tracker, Approved Porsche Warranty, all three keys, service history, just had the 48000 mile service (£1500), Climate, and went like stink, i thought my 2.5 was pretty quick but this was mind blowing.
I cant believe my luck, Its better than sex (well it would be if i could remember what that was like)
£21000 but only gave me £9000 for mine as trade in, pick it up in two weeks,
Glyn
Glyn,
Nice one - hope the S is all you want it to be! Maybe I should do the same.......
]
Meanwhile, still not sorted mine. I might try the hall sensor next. I had problems on my old Golf VR6 with this, and they are normally quite easy/cheap to replace.
Will keep the forum posted.
Cheers,
Jules
Nice one - hope the S is all you want it to be! Maybe I should do the same.......![
]Meanwhile, still not sorted mine. I might try the hall sensor next. I had problems on my old Golf VR6 with this, and they are normally quite easy/cheap to replace.
Will keep the forum posted.
Cheers,
Jules
Never thought of that, you know it just could be as the drop in revs is just like turning the ignition off and then back on before the engine dies.
The hall effect sensor is a magnetic switch (proximity) but why would the cold make a difference to a magnetic sensor, not sure if magnetism is affected by temperature.
Well i changed everything else i could think of without sucess and the check by the OPC on the computer failed to find anything but they never kept it overnight and had a cold start - they told me to just ignore it.
You know what Jules you could have nailed this.
Although i will not be doing any more work on my 2.5 let me know how you get on - if you are right i will kick myself for not thinking of it, i hate being beaten by an engine
Glyn
The hall effect sensor is a magnetic switch (proximity) but why would the cold make a difference to a magnetic sensor, not sure if magnetism is affected by temperature.
Well i changed everything else i could think of without sucess and the check by the OPC on the computer failed to find anything but they never kept it overnight and had a cold start - they told me to just ignore it.
You know what Jules you could have nailed this.
Although i will not be doing any more work on my 2.5 let me know how you get on - if you are right i will kick myself for not thinking of it, i hate being beaten by an engine
Glyn
Well, I thought it would be a straight forward task.
Seems the AOS (Ar$e 'ole 5hitbag) is in the way of the camshaft position sensor (CPS):
http://img.photobucket.com/albums/v727/jcorallo/porsche/AOS/dfd0547b.jpg
You can just see the CPS hiding behind the bellows at the bottom of the AOS.
Talking of the AOS, I cant see any splits in the bellows from this pic - but I noticed they were very soft to the touch and seem very flimsy. I've already bought replacement bellows and they feel much thicker/tougher so they'll be going on as part of this.
I wont be able to do this till next weekend now - but will update the post when I've done the job.
Jules
Seems the AOS (Ar$e 'ole 5hitbag) is in the way of the camshaft position sensor (CPS):
http://img.photobucket.com/albums/v727/jcorallo/porsche/AOS/dfd0547b.jpg
You can just see the CPS hiding behind the bellows at the bottom of the AOS.
Talking of the AOS, I cant see any splits in the bellows from this pic - but I noticed they were very soft to the touch and seem very flimsy. I've already bought replacement bellows and they feel much thicker/tougher so they'll be going on as part of this.
I wont be able to do this till next weekend now - but will update the post when I've done the job.
Jules
Glyn,
I dont suppose you'd let me know your VIN would you? Maybe email it to me if you dont want the world to know it?
I'm interested to know if your car was near mine on the production line...
If you dont want to give me the VIN, just the last 5 or 6 digits would be great. Mine is 601428 so that means number 1428 off the production line. So quite an early one with all the inbuilt faults.
Jules
I dont suppose you'd let me know your VIN would you? Maybe email it to me if you dont want the world to know it?
I'm interested to know if your car was near mine on the production line...
If you dont want to give me the VIN, just the last 5 or 6 digits would be great. Mine is 601428 so that means number 1428 off the production line. So quite an early one with all the inbuilt faults.
Jules
Hi Glyn,
Thanks for that. Yes ours are quite close on the line, but not as close as I would have hoped to be honest...
I actually against my better judgement, put a brand new MAF in this weekend and the problem still exists. However the engine is much more lively and pulls much much harder so I'll be keeping that.
I guess I'm just going to have to go through checking/changing everything as I go.
Camshaft Position Sensor and AOS system next and leak checking. However, it really really could be anything, including faulty ECU programming from new. OH to have access to a PST2.
Does anyone know anything about the vario-cam programs in these engines? What RPM's are things meant to happen with these?
How about knock control?
Anyone got any more straws for me to grab at?!?
Jules
Thanks for that. Yes ours are quite close on the line, but not as close as I would have hoped to be honest...
I actually against my better judgement, put a brand new MAF in this weekend and the problem still exists. However the engine is much more lively and pulls much much harder so I'll be keeping that.
I guess I'm just going to have to go through checking/changing everything as I go.
Camshaft Position Sensor and AOS system next and leak checking. However, it really really could be anything, including faulty ECU programming from new. OH to have access to a PST2.
Does anyone know anything about the vario-cam programs in these engines? What RPM's are things meant to happen with these?
How about knock control?
Anyone got any more straws for me to grab at?!?
Jules
Guest
New member
Jules,
Sorry to hear the MAF sensor didnt work, my boxster is exhibiting the exact same problem. Im going to my local specialist this weekend (Hartech in Bolton) to see if they can sort it out. I recently had mine serviced (a big one). All coil packs replaced, plugs, filters blah, blah a 6 page diagnostic telling me no errors and no problems. They did say that the idle wasnt quite as smooth as it ought to be and suspected the MAF or O2 sensor to be on its way out. So thats what they're going to change.
Incidentally, everyone here seems to know where to look at this sort of thing, I have no idea where the MAF is or worse still how to look at the bleedin' engine! They're charging £250 + Vat to change this MAF does that sound reasonable to everyone?
One symptom that you didnt mention that mine does is that at speed say 50 -60 in fifth, if Im at the "magic" rev range and just cruising the ride is very jerky like its misfiring. Does yours do that?
Cheers
Rod
Sorry to hear the MAF sensor didnt work, my boxster is exhibiting the exact same problem. Im going to my local specialist this weekend (Hartech in Bolton) to see if they can sort it out. I recently had mine serviced (a big one). All coil packs replaced, plugs, filters blah, blah a 6 page diagnostic telling me no errors and no problems. They did say that the idle wasnt quite as smooth as it ought to be and suspected the MAF or O2 sensor to be on its way out. So thats what they're going to change.
Incidentally, everyone here seems to know where to look at this sort of thing, I have no idea where the MAF is or worse still how to look at the bleedin' engine! They're charging £250 + Vat to change this MAF does that sound reasonable to everyone?
One symptom that you didnt mention that mine does is that at speed say 50 -60 in fifth, if Im at the "magic" rev range and just cruising the ride is very jerky like its misfiring. Does yours do that?
Cheers
Rod
Hi Rod,
Can you post up what model and year your Boxster is? Also, can you let me know the last 6 digits of your VIN as well?
The O2 sensors on mine are new as is the MAF. I originally had a fault on the O2 sensors when I purchased the car start of this year - one had stopped working almost completely.
If the weather holds this weekend I'll be doing some leak checking. Apart from the AOS system, I'm also going to be looking at the oil filler pipe area because this was known to crack and leak on early models. There is also the EVAP system to check. Oh joy. But I'm sure I'll find it soon. I will look at the CPS soon as well as thats another candidate but its hidden away behind the AOS so not a 2 min job.
Regarding your magic rev range, I generally get "part throttle hesitation" which happens at rpm's anywhere from idle upwards - this is of course more pronounced lower down the rev-range and when in lower gears, and less pronounced and fading away completely as the revs increase, maybe past 3000/3500rpm range (<-- I'm guessing this figure), and/or in higher gears.
Let us know how you get on with Hartech!
Cheers,
Jules
Can you post up what model and year your Boxster is? Also, can you let me know the last 6 digits of your VIN as well?
The O2 sensors on mine are new as is the MAF. I originally had a fault on the O2 sensors when I purchased the car start of this year - one had stopped working almost completely.
If the weather holds this weekend I'll be doing some leak checking. Apart from the AOS system, I'm also going to be looking at the oil filler pipe area because this was known to crack and leak on early models. There is also the EVAP system to check. Oh joy. But I'm sure I'll find it soon. I will look at the CPS soon as well as thats another candidate but its hidden away behind the AOS so not a 2 min job.
Regarding your magic rev range, I generally get "part throttle hesitation" which happens at rpm's anywhere from idle upwards - this is of course more pronounced lower down the rev-range and when in lower gears, and less pronounced and fading away completely as the revs increase, maybe past 3000/3500rpm range (<-- I'm guessing this figure), and/or in higher gears.
Let us know how you get on with Hartech!
Cheers,
Jules
Guest
New member
Took the car to Hartech today, the guy there, Grant, took it out and he said it was running bad. He said there were lots of faults recorded, some of which were pointing at the O2 sensor (oh crap). He changed the MAF sensor and the car drastically improved. I can feel the car pulling much much harder and smoother.
Also one thing that used to annoy me has improved a lot. In slow traffic it used to be a nightmare to try and get a slow cruise, it was as if the spring on the accelerator was very strong and the pedal was also sticking, so I was having to press hard to overcome the sticking and then it would jerk away. Very annoying. Anyway that seems to be much better.
The idling is much steadier too. I'll put another post on later to let you know what its like starting from cold, because the car was warm when I picked it up.
In summary the car is much much improved, Im not 100% convinced it is 100% yet, but changing the MAF Sensor certainly improved the car.
Too be continued....
Rod
Also one thing that used to annoy me has improved a lot. In slow traffic it used to be a nightmare to try and get a slow cruise, it was as if the spring on the accelerator was very strong and the pedal was also sticking, so I was having to press hard to overcome the sticking and then it would jerk away. Very annoying. Anyway that seems to be much better.
The idling is much steadier too. I'll put another post on later to let you know what its like starting from cold, because the car was warm when I picked it up.
In summary the car is much much improved, Im not 100% convinced it is 100% yet, but changing the MAF Sensor certainly improved the car.
Too be continued....
Rod
Shame about that Rod - these sort of things can be really expensive especially if you ask a garage to try and fix them.... []
I should get round to the camshaft position sensor soon - however, I'm finding it hard to resist removing the whole intake manifold first this weekend, to be able to check everything over... and to be able to get to see the various air pipes up close... there are so many things it could be, but a few tests have suggested it could be an air leak. However, if it is an air leak, I'm prone to thinking its coming from more than just one part - like lots of little leaks - a bit here and a bit there - my car is 10 years old after all so maybe everything has relaxed a little...!
There are so many things it could be!!! [][]
Jules
]I should get round to the camshaft position sensor soon - however, I'm finding it hard to resist removing the whole intake manifold first this weekend, to be able to check everything over... and to be able to get to see the various air pipes up close... there are so many things it could be, but a few tests have suggested it could be an air leak. However, if it is an air leak, I'm prone to thinking its coming from more than just one part - like lots of little leaks - a bit here and a bit there - my car is 10 years old after all so maybe everything has relaxed a little...!
There are so many things it could be!!! [
][]Jules
OK guys the problem is now solved!
Yesterday I decided to strip off all the intake piping and throttle body and check for leaks.
I found two significant problems and one minor problem:
1) One of the large hose clamps that secures the rubber sleeve to the intake distributor seemed to come undone a bit too easily. I never did check these for tightness... The suspect one was on the left side of the engine serving cyls 3,4 and 5.
2) The idle air control valve, although looked very clean and dry and not gummed with oil, was "crunchy" when I pushed the swing door back with a small screwdriver. There was a layer of carbon causing it to bind slightly. Once cleaned off, the door moved very freely.
3) There was a slight "plug" of thick oil in the signal line to the Fuel Pressure Regulator which I blew out. I also cleaned the throttle body out completely and removed a very thin layer of oil from the inside.
I also hoovered out the air filter sponge and cleaned and de-greased all parts before reassembly.
Once back together, I reset the DME and the difference was superb.
Rock solid idle, no cut out at 1400rpm and part throttle is as smooth as anything. No more surging or hesitation. Transition from idle to any rpm and back is now as you would expect - flawless.
Regarding point 1) above. When I'd put the intake back together and started the engine up, viewing the running engine from the drivers seat (I had both access panels removed) I noticed how much the plastic intake manifolds (intake distributors) moved relative to each other at different levels of throttle due to the vacuum inside. I actually measured it! At idle, the two intake manifolds are a good 2mm closer together. Open the throttle and let air in quickly, and they "relax" outwards. You can also see the flat top section (that says Porsche on) collapses in a couple of millimeters at idle, and springs out when you open the throttle.
Given that these manifolds move about so much, you can see a loose clamp would cause havoc - item 11 in the pic below (the one that was loose on mine was the 2nd one in, going left to right)...
Cheers,
Jules
Yesterday I decided to strip off all the intake piping and throttle body and check for leaks.
I found two significant problems and one minor problem:
1) One of the large hose clamps that secures the rubber sleeve to the intake distributor seemed to come undone a bit too easily. I never did check these for tightness... The suspect one was on the left side of the engine serving cyls 3,4 and 5.
2) The idle air control valve, although looked very clean and dry and not gummed with oil, was "crunchy" when I pushed the swing door back with a small screwdriver. There was a layer of carbon causing it to bind slightly. Once cleaned off, the door moved very freely.
3) There was a slight "plug" of thick oil in the signal line to the Fuel Pressure Regulator which I blew out. I also cleaned the throttle body out completely and removed a very thin layer of oil from the inside.
I also hoovered out the air filter sponge and cleaned and de-greased all parts before reassembly.
Once back together, I reset the DME and the difference was superb.
Rock solid idle, no cut out at 1400rpm and part throttle is as smooth as anything. No more surging or hesitation. Transition from idle to any rpm and back is now as you would expect - flawless.
Regarding point 1) above. When I'd put the intake back together and started the engine up, viewing the running engine from the drivers seat (I had both access panels removed) I noticed how much the plastic intake manifolds (intake distributors) moved relative to each other at different levels of throttle due to the vacuum inside. I actually measured it! At idle, the two intake manifolds are a good 2mm closer together. Open the throttle and let air in quickly, and they "relax" outwards. You can also see the flat top section (that says Porsche on) collapses in a couple of millimeters at idle, and springs out when you open the throttle.
Given that these manifolds move about so much, you can see a loose clamp would cause havoc - item 11 in the pic below (the one that was loose on mine was the 2nd one in, going left to right)...
Cheers,
Jules
Posts made and opinions expressed are those of the individual forum members
Use of the Forum is subject to the Terms and Conditions
