Porsche 911UK Forum

Welcome to the @Porsche911UK website. Register a free account today to become a member! Sign up is quick and easy, then you can view, participate in topics and posts across the site that covers all things Porsche.

Already registered and looking to recovery your account, select 'login in' and then the 'forget your password' option.

Ticking over like a bag o' spanners - Fixed

At the moment its gone from intermittent fault to intermittent running well.

Think I'll strip the plenum down, clean it out again and see if it runs well. If it's still lumpy, then get a couple on knock sensors. Good chance if it is a knock sensor, it's only one, but may as well do both whilst I'm in there.


Checked my spark plugs the other day and they all look perfect and identical on both banks. Next time I hear someone on here bitch about changing plugs or coil packs I'm gonna show them my hands and arms after taking those knock sensors off (with the engine hot!!!!!!) :grin:

Now they are a swine of a job - especially when you drop a 12mm socket on top of one bank!!
 
You have my sympathys .. hot engine plus that kind of job .. its not pleasent .

Take a few pictures as you go please , vacumn pipes , amount of oil in throttle .. that sort of thing .. anything helps me atm to be honest :)
 
I feel for you Alex good luck with it hope you can get to the bottom of it soon :thumb:
 
Re step 14 in your sequence, I'm not familiar with the specific set up but in my experience, differences left to right indicate a fault on one side or the other, not with a common component (such as the maf, plenum or throttle body). More likely a vacuum / manifold leak or o2 sensor on one side imo.

Good luck.
 
Demort said:
Some info on knock sensors ..

http://vems.hu/vt/help/v3/v3_knock_control.html

I think its unlikely the knock sensors are faulty .. possible but very unusual and with out a fault code ? hmm ...

Only way to prove is to scope them im afraid.

I take it you tightened them up to 20nm , they are pressure sensitive so over tightening them will break them , and you can see from the link what they do and how they work so ill not repeat that.

i didnt read all the posts so can you confirm for me this is an idle problem ?

Can you post the adaption figures you have .. which must be a few days driveing since you cleared any fault codes as this will reset the adaption figures.

Atm it sounds like 1 bank is rich and the other is weak .. thats into the lambda sensor / maf sensor fault area or exhaust fault .. blocked cat etc , air leak near lambda sensor .. that sort of thing.

If we are talking idle then can you see the throttle pedal values and throttle position values ?

If so post them and also watch them as you depress the throttle slowly .. tell me at what figure the revs increase and also with the air con on if you can maintain 1500 rpm .. im hopeing you can as if you have basically 1k or 2k with a/c on and cant maintain inbetween with engine hot then its similar to a fault i had recently .. that was a DME .. but that did show random throttle valve fault codes.

Ill look at the data and check my fuel sheets at work ( different ones for different models and i havent memorised them :) ) i can also chat with the guys and see if we can think of anything ..

Please bear in mind .. its a hell of a lot easier to fault find when i can work on the car than here but ill do my best.

Post here or PM .. either is good.

Demort, I have read a few posts you have written now on this forum and would like to say what an asset you are for everyone here. Thank you for the support, the likes of which you have shown here :worship:
Alex, the last comment by Grifter above concurs with my thoughts. I wish you the best of luck with finally getting to the bottom of this issue :thumb:
 
Hi Alex
been following this with interest

I am intrigued by the difference in fuel trims between banks - i think you need to understand why there is a difference

It could be the O2 sensors (need to swap them round maybe or scope them)
or it could be some sort of leak (vacuum or fuel depending on rich or lean)

If you can show that the O2 sensors are working ok then you can systematically search for leaks with quick start / propane gas)

I recently spent some hours watching youtube videos from a guy called schrodingers box - quite interesting
 
digby said:
Hi Alex
been following this with interest

I am intrigued by the difference in fuel trims between banks - i think you need to understand why there is a difference

It could be the O2 sensors (need to swap them round maybe or scope them)
or it could be some sort of leak (vacuum or fuel depending on rich or lean)

If you can show that the O2 sensors are working ok then you can systematically search for leaks with quick start / propane gas)

I recently spent some hours watching youtube videos from a guy called schrodingers box - quite interesting

If the fault was intermittent, then there most of the time, then disappears when I swap the knock sensors, remove the plenum , cleanout and refit, then return the day after, how can you explain any of the above?

Previously checked for leaks with easy start about 4 pages back.

:?
 
Hi Alex

intermittent symptoms are (i guess) generally caused by intermittent problems like a bad electrical connection or a leak that only happens under certain circumstances.

these are of course the worst problems to track down .....

you have clues though - the difference between banks 1 and 2 should help a lot

if you make the fuel trim problem change banks by swapping something then you are in business

watch the videos this guy has made and if your diagnostics can do short and long term fuel trims and actual graph the O2 sensor outputs then you are in business

good luck

p.s. when my 996.1 had a bad idle it needed (had) a new camshaft solenoid thing
 
[/quote]

Demort, I have read a few posts you have written now on this forum and would like to say what an asset you are for everyone here. Thank you for the support, the likes of which you have shown here :worship:
[/quote]

Very decent of you to say so sir .. just trying to help though :)

Maf sensor i mentioned .. it was for a reason .. rich / lean on opposite banks .. say we have an air leak on bank 1 .. not good but the car will adapt by injecting more fuel and so run fine .. but a faulty maf can over and under fuel .. the maf is not obvious as the adaptions point to something else but trust me it is possible ..

You can also get a misfire on say 4,5 and 6 which points to a vario cam fault .. again it can be the maf .. been there seen it and got caught out .. hence i mentioned it.

Also im looking for difficult to find faults .. something unusual because im dam sure Alex knows what hes doing so pointing out the obvious is in my way of thinking a bit insulting to him .

Anyways just pointing out why may be disconnecting the maf and driveing is a possible if unlikely fault .. or if its been replaced in the last few years then it can be eliminated.

Im going to read the entire post and see what i can come up with .. back in 20 mins or so i guess .. its a long post !
 
ragpicker said:
My friend (who is my Indy) had this issue on a car he had in a few weeks ago.
He spent literally days trying to figure it out - changing lambdas, crank sensor, throttle sensor, plugs, packs, earth points, engine out looking for air leaks etc. I'm not joking he spent 3 straight days on it (this is the reason my car took so long to get in to have my problem sorted).

He has also got a 3.4 carrera. In the end he took his ECU and loom from his car and put it into the car with the problem. Bingo! Problem of rough idle sorted instantly. Symptoms were exactly the same as you have described.

When he plugged the faulty cars ECU into his car - the problem was there again.

This is the 3rd time he has seen this problem apparently.

Fortunately ECU's with keys can be found on eBay for about £100 but it must be the same engine model number as yours. There was a bit of an ECU changeover at the end of the 3.4 production run apparently.

Give Nelson Porsche a ring (stockton on tees) - say Ragpicker sent you :wink:

I got as far as this then stopped reading .. its also what i was thinking and i posted before reading this which makes it even worse im afraid as 2 of us have come to the same conclusion independantly.

Mine was a bitch of a problem to find as well but i did have thottle body codes , random ones but a pointer at least.

Heres what i tryed to try and prove it , which i want you to try please ..

You know where the dme is .. it gets hot .. very hot , stupid place to put it if you ask me .. remove the carpet , remove the bracket and have the dme face up , so hopefully it stays cooler , then try a drive and see if any difference.

A reprogram is a possible but my one we just replaced it to fix it.

Couple of other things you may want to consider , i made some notes as i was reading from the beginning ..

Tank venting , happens at operating temp , need to find a way of blocking the pipe , vent pipe left open i think would be safest and seeing if that makes any diff .. not sure the best way to do it .. but you know what i mean.

Lambdas .. they work from about 1 min after cold .. fault would be there before operating temp i feel.

Vario cam is a possible , it will affect idle .. but ive always seen rough running or misfires with that fault , it wont stop the car from starting either .. possible but im unsure .

Erm the pict of the AOS .. thats an earth lead there next to it .. might be an idear to clean it or at least check its a good contact as it doesnt look like it lol ... not sure off hand what its for but it will be sensor related .. probably nothing to do with the fault .. but even so :)

The fault itself .. dme monitors crank sensor and so rpm , if it drops below 700 it will increase the throttle to raise the rpm .. this is a constant thing so it will continually alter the throttle to maintain idle.

Your car is not reacting untill it drops almost to stall then bangs open the throttle to catch it .. over reving to a point and then repeating .. crank sensor is main input .. dme is in charge , throttle pedal position and throttle position all have inputs to decide idle .. hence i wondered if you could see any of these values ..

Pedal can cause something like this .. its yet another possible .. but im also back at the DME as well ..

Very hard without spending a fair bit of time on the car to help .. but hopefully something ive posted will be usefull .. please keep posting though of what you do / decide .

As i say to some of the guys with a bitch of a problem .. Good Hunting .


EDIT one other thing i did think of which you may already have tryed is check the fuel pressure at the rail .. low pressure wont give fault codes and can cause varying faults.
 
systemmeister said:
Is it lumpy as a cement mixer?

I had similar symptoms but mine was vario cam solenoid.

Problem now sorted. Was variocam solenoid on Bank 1. :oops:

Shoulda listened to you Jon in the 1st place :bonk:
 
All a bit late in the day and would not have solved your issue Alex... When trying to detect air leaks I use a length of hose one end to my ear the other used to move around the areas of interest...

Showing my age again, I also used that system for balancing carburettor air flow in twin/multiple carb set-ups.. Simple cheap and no need for a fire extinguisher.. :?:
 
Over 2 weeks of perfect running now. I'm convinced now the problem is resolved. Spent 2 weeks waiting to fire it up when hot and the tickover be lumpy.

Alex is a happy man. :)
 

New Threads

Forum statistics

Threads
124,354
Messages
1,439,461
Members
48,713
Latest member
3sp1f8
Back
Top