Idle Problems

[Chesp123]

Audi A4 B5 1.9tdi, 2000 (W) with 180,000 miles.

I have the above car which has been experiencing idle problems while stopped in traffic.
The revs jump from 800 to 1,100 constantly, but as soon as the gear is initiated and driving normally the car runs without problems other than a slight misfire around 2000 revs...

I've already had the EGR and Intake Manifold off and cleaned, but hasn't solved the problem.

My next thought is there could be an air leak somewhere but have no idea how this can be diagnosed, someone suggested a smoke test, but didn't know where to blow the smoke into...

If anyone has any ideas then it would be most appreciated!

Thanks,

Ches

[Chesp123]

Anyone any ideas at all?

Few things to add, the car doesn't start first time, but usually second or third after turning ignition for a few seconds.
Not sure what could be causing this other than the glow plugs.

Had fault codes read with VCDS before xmas and only the following appeared:
Auto HVAC - 00792 0 A/C Pressure Switch (F129) 31-00 - Open or Short to Ground

This could have something to do with it as when i turn the Air Con on, the engine shudders slightly and is more prone to erratic idling when the engine is warm, as apposed to the idle pin just moving up and down rythmically while stopped in traffic and Air Con turned off...

[yaman]

Two things spring to mind here,

Coolant temp sensor

Injector wiring loom (PD engine)

Regards
Jim

[Chesp123]

Hmm, how could the coolant temp sensor affect the engine idle?

Have read lots about the Injector Wiring Loom, lots of people suggesting a new one would solve the problem, but most saying that it will not make a difference and is a common answer on forums ultimately costing money needlessly.

Audi don't seem to know how to solve it either without hooking it up to VCDS and even then if no codes come up they are stumped and want you to book the car in so they can replace the majority of the parts at huge cost, so wouldn't like to be in that position, i may as well drop my trousers in advance of the rogering i would inevitably be about to recieve...

[delambo]

someone suggested a smoke test, but didn't know where to blow the smoke into...

LOL - I dont think they meant blowing smoke in - more measuring the smoke from the exhaust - but I think they are confusing it with a petrol. When a petrol vehicle has an air leak it will show up with an emissions test - but not with a diesel. Also I would suggest an air leak would not give these symptoms on a diesel - let alone a tdi. First place to start would be a fault code read, it might be something simple - Audi are not the only ones who can read fault codes; find a decent friendly local garage, or maybe a local forum member with vag-com who might read you codes for a couple of beer tokens.

[Chesp123]

Think it was more to find if there was a cracked pipe or tube going in our out of the engine, but the guy who gave me the advice works for Jaguar and is more of a plug the computer in technician than an old school mechanic...

I've had the codes read using VCDS before xmas and only the following came up:
Auto HVAC - 00792 0 A/C Pressure Switch (F129) 31-00 - Open or Short to Ground

The car passed it's emissions test in October when it came through the MOT, so unless the test isn't as conclusive as i think it is?

[chrismaher2007]

Mine turned out to be dirty throttle body last time this happened. Cleaned and recalibrated sorted it.

Exactly same symptoms.

[acmo]

Hmm, how could the coolant temp sensor affect the engine idle?

You will be surprised!

[Chesp123]

Mine turned out to be dirty throttle body last time this happened. Cleaned and recalibrated sorted it.

Exactly same symptoms.

As far as i know diesel engines don't have a throttle body, I've already had the EGR and inlet manifold off and cleaned both with carbon spray, neither had any notable build up in them and since i put them back on there has been no difference in symptoms. do you think i need a new EGR valve?

[Chesp123]

You will be surprised!

Care to elaborate? :-)

[hibbsy21]

Care to elaborate? :-)

Well simply put, when an engine is cold (or being told it is cold by the temp sensor) then it runs on fast idle to warm it up. Almost all cars will do this, its just a way to warm things up quicker if you sit for a while before setting off.

Sent from my HTC Desire HD using Tapatalk

[acmo]

Care to elaborate? :-)

From past experience the Coolant Temp Sensor can play havoc with running conditions as the ECU relies of it for fuelling. For the sake of a small expense its worth giving it a go. Don't get a cheap one, waste of time.

[Chesp123]

Sounds promising as it could also explain the cold starting issues i've been having, takes 3 to 4 goes before it starts up sometimes.

Can you advise how i go about replacing it once i've sourced the part?

[acmo]

Dead easy, unplug connector slide out plastic retaining clip, check they are the same if so throw the old one for the dog!
Remember to do it when engine is cold!
Autodata suggests its towards the back of the block near an injector, it should be in a plastic housing and blue or green in colour

[chrismaher2007]

Engine coolant temperature sensor might not be the same colour as the original. I think that they swapped from black to green sometime but maybe someone with experience can confirm. Ive seen them in blue aswell.

Inspect the crankcase breather pipe aswell. Thats suspect number one for a split pipe. Its at the back of the engine. It can crack and drop oil onto a sensor underneath it. Not sure what sensor it is but it may well be the Engine temp sensor and you might also find out thats why your sensors gone dodgy.

[Chesp123]

Thanks will phone Audi tomorrow as my local europarts don't stock the coolant temp sensor, will also make sure i get a new o ring and the other connector thing. Will report back with the result. cheers

[delambo]

the guy who gave me the advice works for Jaguar

and is therefore not used to working with diesels. Like I said the advise about the smoke test applies to the exhaust emmissions and will help diagnose a vaccuum leak but since yours is a turbo diesel this test does not apply.


I've had the codes read using VCDS before xmas and only the following came up:
Auto HVAC - 00792 0 A/C Pressure Switch (F129) 31-00 - Open or Short to Ground

That code only applies to the air conditioning, whilstplugged in to vag-com (or similar) though it is important to take some live readings to compare with normal values.


The car passed it's emissions test in October when it came through the MOT, so unless the test isn't as conclusive as i think it is?

As I said the test only applies to petrol engines.

[Chesp123]

Going to attempt to fit the new coolant temp sensor i bought from Audi, tomorrow, got the rubber gasket also.
Some people have mentioned a retaining clip, is this something that can be re-used once i've taken it off the old one or should i have bought a new clip?
I've also bought some G12 coolant to top up the reservoir afterwards.

[chrismaher2007]

Its the o ring that 100% needs replacing. Thats for sure.

I just reused retaining clip as it doesnt malform or shrink like the oring. Its the same clip used in several locations on car like the crankcase breather pipe which is above the sensor.

When you unplug sensor expect coolant to shoot out. If it does dont panic it will stop and you can refill. Work on a cold engine and twist off coolant tank lid to minimise it.
I did it with warm engine first it happened then with cold engine and it sill happened so im not sure the full solution.

All your doing is popping out clip with flat screwdriver and pulling out sensor. replace with new one and put back in. simple enough.

Also i hope you got the correct sensor. Short is 98-99 and longer one is late 99-00 i think.

If you have the wrong one, take out the old oring and then realise youve the wrong one youll end up in a bad situation. ive heard people use that white plumber stuff for pipes if they need a temporary fix.

You wouldnt believe the difference it made to my car when replaced. Car starts perfect everytime , Revs lock onto 1000 and throttle is a lot more responsive. Feels like a new car again.

old one http://www.micksgarage.ie/img/td/244/s/82037-0.jpg new one http://www.micksgarage.ie/img/td/244/s/82105-0.jpg

[Chesp123]

Its the o ring that 100% needs replacing. Thats for sure.

I just reused retaining clip as it doesnt malform or shrink like the oring. Its the same clip used in several locations on car like the crankcase breather pipe which is above the sensor.

When you unplug sensor expect coolant to shoot out. If it does dont panic it will stop and you can refill. Work on a cold engine and twist off coolant tank lid to minimise it.
I did it with warm engine first it happened then with cold engine and it sill happened so im not sure the full solution.

All your doing is popping out clip with flat screwdriver and pulling out sensor. replace with new one and put back in. simple enough.

Also i hope you got the correct sensor. Short is 98-99 and longer one is late 99-00 i think.

If you have the wrong one, take out the old oring and then realise youve the wrong one youll end up in a bad situation. ive heard people use that white plumber stuff for pipes if they need a temporary fix.

You wouldnt believe the difference it made to my car when replaced. Car starts perfect everytime , Revs lock onto 1000 and throttle is a lot more responsive. Feels like a new car again.

old one http://www.micksgarage.ie/img/td/244/s/82037-0.jpg new one http://www.micksgarage.ie/img/td/244/s/82105-0.jpg

Thanks, I've read that if you unscrew the cap on the coolant reservoir to release the pressure then screw it back on tight the coolant loss when rereplacing the sensor is significantly reduced as it creates a vacuum to keep the coolant in the reservoir, will give that a try and post back the result. i bought the new style sensor and have checked it with the existing one and it matches.

[Chesp123]

OK so i fitted the new coolant temp sensor, took it for a drive to warm the engine and the rough idle problem is still there, but only when the engine gets to around 80 degrees.
Car also doesn't start first time, most of the time it fires up second time but only after cranking it for around 6 or 7 seconds with the clutch pressed in.

Now i'm thinking that there must be a split pipe somewhere as i've already cleaned both EGR and Intake Manifold and while there wasn't much gunk in either i cleaned both anyway.

Anyone got any other ideas or can advise anyway that i can check the pipes to find the source of the air leak if there is one?

[chrismaher2007]

Is the VAGCOM Cable bringing up any errors? maybe clear them and go for another drive and see what comes up.

Id say it might be worth just giving it an hour in an Audi garage and get a diagnosis

[Chesp123]

Is the VAGCOM Cable bringing up any errors? maybe clear them and go for another drive and see what comes up.

Id say it might be worth just giving it an hour in an Audi garage and get a diagnosis

No access to VAGCOM unfortunately, will see if i can get a cheap quote for VCDS diagnostic check and see what it throws up... Do you think disconnecting the battery for a few minutes to reset the computer will help it to recongnise that it now has a new coolant temp sensor installed? Seems strange that the car should recongnise a new part straight away without a restart as you would with fitting a new part in a PC for instance...

[chrismaher2007]

I disconnected the battery while i was replacing the sensor anyway so its worth a shot.

[Chesp123]

resetting the ECU didn't make any difference, however i've had the codes read and it's throwing up, the below...

17965/P1557/005463 - Charge Pressure Control: Positive Deviation


Possible Symptoms

Reduced power output
Limp mode

Possible Causes

Boost Pressure too High
Hoses/Pipes incorrect connected, disconnected, blocked or leaking
Charger Pressure Control defective
VNT (variable nozzle turbo): nozzles stuck
Solenoid Valve for Boost Pressure Control (N75) defective

Possible Solutions

Check Hoses/Pipes to/between Components
Check Solenoid Valve for Boost Pressure Control (N75)
Check / Clean / Replace Charge Pressure Control
Check / Clean mechanism for variable nozzles
Category: Fault Codes


The car has recently been going into temporary limp mode, most of the time when I restart the car limp mode will go away for the remainder of the journey.

Have read that buying innotec audi turbo cleaner will help this, as the vanes inside the turbo get gunked up and stop them from opening/closing, thus creating overboost.

Trouble is i have no idea how to get access to the turbo, can it be done from the top (through bonnet) or do i need to jack it up or get it on a jig and approach from the bottom?

Hopefully someone else who has attempted this can shed some light... Thanks in advance.

[mumutley]

Hello chesp123

Check this thread out http://www.vwaudiforum.co.uk/forum/showthread.php?128851-Turbo-Problem

Its incredible how a split vacum pipe or turbo pipe or intercooler, can affect the running of a TDI
I would be tempted, to remove battery terminals and spend a few hours checking all vacum pipes and turbo pipes for splits, holes ETC (perhaps before you do this, start car and get someone to rev the engine for you whilst looking over turbo pipes ETC are there any collapsing under load?)
Ensure you reconnect all pipe correctly
Just take you time and go through them all.
Good luck

[Chesp123]

Hello chesp123

Check this thread out http://www.vwaudiforum.co.uk/forum/showthread.php?128851-Turbo-Problem

Its incredible how a split vacum pipe or turbo pipe or intercooler, can affect the running of a TDI
I would be tempted, to remove battery terminals and spend a few hours checking all vacum pipes and turbo pipes for splits, holes ETC (perhaps before you do this, start car and get someone to rev the engine for you whilst looking over turbo pipes ETC are there any collapsing under load?)
Ensure you reconnect all pipe correctly
Just take you time and go through them all.
Good luck

Thanks, i have noticed that the exhaust is spewing out white smoke while the engine is ticking over, which would back up the theory of a split pipe somewhere (unless white smoke means something else?), can the pipes be checked for cracks without removing them from the car?

I've ordered innotec turbo cleaner so will use that at some point once i've figured out the best way of going about it...

Do you think the rough idle is also a symptom of pipe/turbo failure?

[mumutley]

"White smoke"

Does it use any water?

[Chesp123]

"White smoke"

Does it use any water?

Water from where? How can i check?
If you're thinking its steam im not so sure as it smells strange and i wouldn't recommend breathing too much of it in!!

[Chesp123]

Had the codes read today, and it's showing the following from the Engine block:

17965 - Charge Pressure Control: Positive Deviation
17564 - Manifold Absolute Pressure Sensor (G71): Open or short to ground
17569 - Manifold Temp Sensor (G72): Open or short to ground

I have read that all of these codes can be fixed if i replace the MAP sensor, so will be trying that first.

Was wondering if anyone else has had this combination of fault codes all at the same time.

The surging while idling is still there, and it occasionally goes into limp mode (which is rectified the next time i start the engine) and it can also stall when coming to a stop.
If the engine has been running for a while it will blow white smoke out the exhaust, which i think is being caused by the failty MAP giving the engine too much fuel as fuel economy is terrible.

Any help is much appreciated :-)

[MONIES_WORTH_83]

white smoke out the exhaust can mean you're burning water in the engine, it might be getting into the combustion via a failed cylinder head gasket for example. if your engine coolant level is dropping, and there is no noticable leaks from pipes (check the floor when running) then it is being used in combustion- not the intention of an ic engine.

i sounds like you have a multitude of faults, not wanting to worry you but it is fairly high mileage.
the ac pump fault can cause a slight erratic idle, i think, on your car it has a clutch to enage the ac compressor (when you turn the ac on). if this is dicky its turning on and off alot maybe.

[MONIES_WORTH_83]

engine coolant (water + antifreeze) can smell sweet, or odd if the coolant has never been changed. if its that your head gasket is prob gone. see notes below. i wouldnt waste money on engine cleaning products, your issues sound fundamental and wont be cured by £10 products.
boost leaks can happen all over the crap tdi pipework that use bayonet fittings which are total junk,

good luck

[MONIES_WORTH_83]

you could always clean the MAF (not MAP?) sensor. i think if you disconnect the electrical connection on the maf and the car runs better, you could just clean it with spray solvent (now in that case the £10 product would be worth it).

are you still burning water? this needs sorting out first, this is more fundamental

[MONIES_WORTH_83]

too much fuel would give black smoke, i think.

[Chesp123]

white smoke out the exhaust can mean you're burning water in the engine, it might be getting into the combustion via a failed cylinder head gasket for example. if your engine coolant level is dropping, and there is no noticable leaks from pipes (check the floor when running) then it is being used in combustion- not the intention of an ic engine.

i sounds like you have a multitude of faults, not wanting to worry you but it is fairly high mileage.
the ac pump fault can cause a slight erratic idle, i think, on your car it has a clutch to enage the ac compressor (when you turn the ac on). if this is dicky its turning on and off alot maybe.


engine coolant (water + antifreeze) can smell sweet, or odd if the coolant has never been changed. if its that your head gasket is prob gone. see notes below. i wouldnt waste money on engine cleaning products, your issues sound fundamental and wont be cured by £10 products.
boost leaks can happen all over the crap tdi pipework that use bayonet fittings which are total junk,

good luck


you could always clean the MAF (not MAP?) sensor. i think if you disconnect the electrical connection on the maf and the car runs better, you could just clean it with spray solvent (now in that case the £10 product would be worth it).

are you still burning water? this needs sorting out first, this is more fundamental


too much fuel would give black smoke, i think.

Thanks for your replies, i'm more concerned about the fault codes in my last message, the white smoke is not much of a regular occurance and is no more than i've seen coming out of the back of other cars in the cold weather we've been having.

I've already changed the MAF sensor a few months back with geniune bosch part so that can't be the issue.

I've ordered the new MAP sensor, again a bosch part so will see how it reacts to that being fitted at the weekend.

Will monitor the smoke issue a bit more but as i'm usually working on the car on my own it's not as easy to rev the engine and see what comes out the other end!

[Chesp123]

Fitted the new MAP (Manifold Absolute Pressure) Sensor, which is also called the Thrust Sensor tonight and it's got rid of the two codes:
17564 - Manifold Absolute Pressure Sensor (G71): Open or short to ground
17569 - Manifold Temp Sensor (G72): Open or short to ground

However, after clearing all codes the following has remained:
17965 - Charge Pressure Control: Positive Deviation

17965/P1557/005463 - Charge Pressure Control: Positive Deviation
Possible Symptoms


Reduced power output
Limp mode
Possible Causes


Boost Pressure too High
Hoses/Pipes incorrect connected, disconnected, blocked or leaking
Charger Pressure Control defective

VNT (variable nozzle turbo): nozzles stuck

Solenoid Valve for Boost Pressure Control (N75) defective
Possible Solutions


Check Hoses/Pipes to/between Components
Check Solenoid Valve for Boost Pressure Control (N75)
Check / Clean / Replace Charge Pressure Control

Check / Clean mechanism for variable nozzle

I've got the innotech turbo cleaning kit designed for my engine, but haven't managed to find the time to do it yet, has anyone else done this and did it solve the problem?

[jonathanfenton]

So what was the outcome? Have you managed to solve all your issues?

[Chesp123]

So what was the outcome? Have you managed to solve all your issues?

No not managed to find the answer other than my turbo needs to be reconditioned to solve the fault code i mentioned above. if you manage to diagnose the rough idle issue then please let me know!! :-)

[Chesp123]

Update: the car won't start, it will try to start but it doesn't fire up. Have tried it with the clutch fully pressed and pumping the accelerator but nothing. On the way home from work last night the car was in safe mode but as this is quite common i just assumed it would start again. guess the time has some to have to spend a load of money on it... anyone got any ideas why its not starting?

[Chesp123]

Finally got the car running spot on today, turned out the cambelt, waterpump and hydraulic tensioner had all gone, and they put new coolant in. 4 hours labour plus parts set me back £480 but the car is running and idling like a dream!

Thanks to everyone who has contributed to this thread, i hope my experiences can help others in the same position :)