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[amba]

Have noticed last few mornings engine is quite lumpy on tickover from cold start ,until the temperature starts to move on the gauge and gets to above 90 then all is nice and smooth.
Any pointers what is causing this and how to cure...plugs and leads are new in last 6 months..breathers are spotless,hbv is also new,and timing is correct.

[cem_devecioglu]

initial estimation : air leak ..

[amba]

Why would it only have an air leak until it has warmed up..well atleast when the temp gauge has gone above 90 ?..I have checked all pipes/hoses and all is as should be..I was thinking that it might be the temp sender to the ECU,as thought I had read somewhere that the temp sender deals with that.I have checked the wires at back (by feal and mirror)and they are all connected.

[cem_devecioglu]

Why would it only have an air leak until it has warmed up..well atleast when the temp gauge has gone above 90 ?..I have checked all pipes/hoses and all is as should be..I was thinking that it might be the temp sender to the ECU,as thought I had read somewhere that the temp sender deals with that.I have checked the wires at back (by feal and mirror)and they are all connected.

old gaskets fail when the metal is in cold state..but when they expand it closes..and there can be other reasons too..

even if after some job they are not torqued properly it can happen..

[cem_devecioglu]

and another estimation is leaky exhaust valves..but thats more complicated to solve..

I had similiar problems in the past and changed  serious number of parts before I solve..

[Andy B]

Why would it only have an air leak until it has warmed up..well atleast when the temp gauge has gone above 90 ?..I have checked all pipes/hoses and all is as should be..I was thinking that it might be the temp sender to the ECU,as thought I had read somewhere that the temp sender deals with that.I have checked the wires at back (by feal and mirror)and they are all connected.

That would be my first thought, as when warm, your car runs off the lambda readings. I've had it the other way round with my Senator when the lambda failed, ran great cold, then ran 'strange' when warm/hot.

[cem_devecioglu]

I think something is disturbing the correct ratio..

[amba]

I am convinced it is temperature related as car runs fine even when cold-(warming up from cold start)-it is just when idling on driveway in morning it is not smooth and revs do fluctuate and this does not stop until temp has reached 90 + which gets me thinking that when lamba readings are being taken when warm all is fine.
Just wondered if anybody else had had or got similar issues...was it cured by replacing temp sender unit and how much of a pain is it to get at and do.

[cem_devecioglu]

your car is 98 model..worth changing anyway..but not sure will solve alone :-/

[matt-sboro]

I am convinced it is temperature related as car runs fine even when cold-(warming up from cold start)-it is just when idling on driveway in morning it is not smooth and revs do fluctuate and this does not stop until temp has reached 90 + which gets me thinking that when lamba readings are being taken when warm all is fine.
Just wondered if anybody else had had or got similar issues...was it cured by replacing temp sender unit and how much of a pain is it to get at and do.

you may be convinced its temperature related but when the TEMP is cold the gaskets will have contracted thus causing an air leak - when the TEMP is warm the gaskets expand and seal the air leak.

its a possibility to look at before you start spending loads of money replacing parts

[ngrainqey]

sounds a bit like what happened on my 2.0, could possibly be egr related or exhaust manifold with an air leak on it

[amba]

So what is the best way to check if exhaust manifold gaskets are leaking..I had them done on a previous omega as i could hear it like a clock ticking until warm..but this car has no such noises.EGR is tight to manifold and metal gasket in place.

[cem_devecioglu]

ok..

here is my idea..

spray carb cleaner around connections and the intake manifold while the engine is running. If you get an rpm change when you spray, it means the vapors are getting in somehow.

Second test

try a compression test when the engine is completely cold..This can be

done with  a pressure gauge with the sparks out and cranking the

engine a few times..

[Techno]

Hold on aren't we going yet a little too deep here?

I had the same problem I did the following: -

1. Clean the Air flow meter, intake air temp sensor and idle speed adjuster valve.
2. Replace/clean air filter.

Worked for me  .

[amba]

It is only a minor issue,which I am reluctant to start doing major stripping down on,especially this time of year.I was unaware that you can clean the MAF ,as thought you would cause more problems than you solve and I can only describe the problem as ther until the gauge goes over 90,hence my logic on the temperature sender unit asonce warmed up all is fine.

[Techno]

To do what I list takes no more than an hour less if you know what you are doing.  All parts are very easliy removed and accessible with nothing more that simple tools required.  

[amba]

Quite accept that they are simple jobs to do and time is no problem..just was unsure how you clean a MAF meter.?

[Techno]

It's easy they get covered in road crud and alike, all I did was use a little brake cleaner and a small bursh  

[amba]

Thought the oil coating on the inside would get messed up.

[Techno]

Hang on are we taking about the same part/s here

Air flow meter, intake air temp sensor are located in the induction system just after the air filter box there should be no oil on them to start with.

Idle speed adjuster valve is located front left hand side of the plenum chamber this is just a rotary valve in a chamber the slave block gets covered in carbon/oil deposits and blocks/sticks thus causing poor idling or stalling.  

By flushing with carb/brake cleaner these deposits are removed it doesn't need oil to operate as it's powered by an electric motor.            

[amba]

Think we are getting a bit at cross purposes..the airflow meter(or MAF)is located on the large pipe running from the air filter.It has a oil coated blade arrangement inside which I thought should not be cleaned as the surface is oil coated and is regulated by warm air flowing across it before it goes through the throttle bodies into the plenum..is this the bit you cleaned with a brush and brake cleaner?

[Techno]

Yes but I don't think it's oil coated as more like some kind of polyurethane material it's certainly wont/it's affected by spaying with carb cleaner and a gentle brushing to remove stubborn road grime. As with all induction systems there is always some level of fuel vapour present so anything placed within the system will be solvent resistant.

[Cliffo B]

Hello,Is it possible your problem could be a breaking down D.I.S unit ?Regards,Cliff. :-/

[amba]

Not dis as fitted new about 2 months ago along with new leads/plugs and hbv,so nothing in that area .Am sure all leads and cables went back correctly as is running perfect,its just this niggle before it warms up.

[Chopsdad]

MDTM maintains the MAF should only be cleaned with keyboard foam cleaner, carb cleaner etc can damage the element.

[cem_devecioglu]

Hold on aren't we going yet a little too deep here?

I had the same problem I did the following: -

1. Clean the Air flow meter, intake air temp sensor and idle speed adjuster valve.
2. Replace/clean air filter.

Worked for me  .

if mentioned parts are dirty why it will work normal when the engine reaches 90 C..

Technically there can be many reasons..and one of the reasons can be an expensive fix..before spending unnecessary money it will be very practical to see the engines condition by compression check..

if cylinder rings are worn or there is a leak from valves whatever you

change wont help.. :-/

[Techno]

The issue is lumpy idle until warm, a loss of compression due to rings or valves will not go away when the engine warms up and there will be a loss of power and drivability.  If the rings are worn you will also get oil loss and smoke due to burning, crankcase overpressure leading to areas of flooding in the emission control system.  If the valves where leaking again a loss of power would be very evident and before long they will burn out with a drastic loss power, other common symptoms will be difficulty in starting and an ever increasing drop in fuel economy.

My understanding of why cleaning the parts I mentioned works (providing there are NO other symptoms other than just lumpy idle) is: -

1. The Air flow meter does just that measure air flow if it's dirty it cant so it thinks it's flowing faster/slower than it is, thus the ECU increases/decreases the mixture slightly giving you either too rich (over choked) or to lean (weak) both will give you a lumpy idle.

2. Intake air temp sensor if this to is dirty it will under/over read the real temperature giving the same result.

3. Idle speed adjuster valve if this is dirty/gummed up it will not respond correctly to ECU signals again giving you a lumpy idle

I'm not an expert and I my be way off with my thinking but in my humble opinion I believe that providing there are no other issues then these are the first port of call.

[cem_devecioglu]

The issue is lumpy idle until warm, a loss of compression due to rings or valves will not go away when the engine warms up and there will be a loss of power and drivability.  If the rings are worn you will also get oil loss and smoke due to burning, crankcase overpressure leading to areas of flooding in the emission control system.  If the valves where leaking again a loss of power would be very evident and before long they will burn out with a drastic loss power, other common symptoms will be difficulty in starting and an ever increasing drop in fuel economy.

My understanding of why cleaning the parts I mentioned works (providing there are NO other symptoms other than just lumpy idle) is: -

1. The Air flow meter does just that measure air flow if it's dirty it cant so it thinks it's flowing faster/slower than it is, thus the ECU increases/decreases the mixture slightly giving you either too rich (over choked) or to lean (weak) both will give you a lumpy idle.

2. Intake air temp sensor if this to is dirty it will under/over read the real temperature giving the same result.

3. Idle speed adjuster valve if this is dirty/gummed up it will not respond correctly to ECU signals again giving you a lumpy idle

I'm not an expert and I my be way off with my thinking but in my humble opinion I believe that providing there are no other issues then these are the first port of call.

A slightly worn rings can do that..Thats the point you are missing..
I remember I read some technical papers about that on the net..

Of course cleaning those will help..But dont expect 100% efficiency from an old engine and old sensors.. I can guarantee a 98 model car regardless of brand model unless stayed in garage for a long period will be worn a bit..

[cem_devecioglu]

here is an interesting page..
http://www.popularmechanics.com/how_to_central/automotive/1272271.html?page=2

"An engine with high mileage that's tired and worn out may not pull a healthy vacuum of 18 to 20 in. Hg at idle (closed throttle plate) anymore. That means the MAP sensor will always read the engine as under load (low vacuum) and--just doing its job--inform the powertrain computer to add more fuel. When the oxygen sensor picks up the rich mixture in the exhaust stream, it will call for a leaner mixture. Common strategy is to open the idle air-bypass valve to let some more air in. But an engine that's just on the borderline of wheezing may intermittently "loosen up," leading to a roller coaster idle. It may have trouble breathing when cold, but once warm-with expanded piston rings, gaskets and the like--show a perfectly healthy intake vacuum. "

[amba]

Thanks for all your input and advise,guys.
I will go the least difficult and most cost effective route first and will do the cleaning atc as suggested by Techno.The car is due a full brake check and other bits in the new year and as this can be done indoors and under cover I will suggest to my mechanic that we undertake a compression test just to see what results are from each cylinder as would be usefull info aswell.
The problem is evident every morning when car is started from cold and this was my thought pattern regarding the temp sender as I understand that this sends a signal to ecu for fueling until the car warms up and then the lambas take over.
This morning the car started first turn as always,but temp took about 5mins in slow traffic before gauge started to register and all the time tickover was erratic with needle moving from 500-750+ and engine feeling very uneven.When the gauge started to move upto 90 and beyond this completely went and the engine ticks over very smoothly,with it now registering mid way on temp gauge (95) and silky smooth tickover.There is no oil loss or usage and the performance from the engine is so good that I have no hesitation in keeping a wonderfull 10 year old car,and relying on it daily for my 100 mile a day job.
The problem is not major,merely of mild concern (well atleast at the moment..I hope).

[cem_devecioglu]

Thanks for all your input and advise,guys.
I will go the least difficult and most cost effective route first and will do the cleaning atc as suggested by Techno.The car is due a full brake check and other bits in the new year and as this can be done indoors and under cover I will suggest to my mechanic that we undertake a compression test just to see what results are from each cylinder as would be usefull info aswell.
The problem is evident every morning when car is started from cold and this was my thought pattern regarding the temp sender as I understand that this sends a signal to ecu for fueling until the car warms up and then the lambas take over.
This morning the car started first turn as always,but temp took about 5mins in slow traffic before gauge started to register and all the time tickover was erratic with needle moving from 500-750+ and engine feeling very uneven.When the gauge started to move upto 90 and beyond this completely went and the engine ticks over very smoothly,with it now registering mid way on temp gauge (95) and silky smooth tickover.There is no oil loss or usage and the performance from the engine is so good that I have no hesitation in keeping a wonderfull 10 year old car,and relying on it daily for my 100 mile a day job.
The problem is not major,merely of mild concern (well atleast at the moment..I hope).

Thermostat and Coolant temperature sensor needs checking..

and another test..try disconnecting the secondary air injection pump..

[omegalad]

ive noticed something in my car i have previous post about this though with the bad judder in my acceleration power loss.
she isnt fixed yet

when the car is cold shes lumpy till warm right?
BUT when i put on the fan/heater on full blast when the engine is cold she gets REALLY rough then i switch it off goes lil smoother. but then when the engine warms up its like normal.


what this mean??

wonder if this is the cause somewhere like a leak? engine airflow not running right etc.??

[MarkG]

If you have an air leak, then you should be able to hear it if you stick your head under the bonnet while the engine is running. wiggle anything that moves to see if it changes pitch. Look in particular at the brake servo vac pipe where it rubs against the AC fitting on passenger side (you would also notice lack of braking power it this is holed) and the narrow bore pipes around the back of the engine drivers side.

Consider also ignition leads starting to break down or worn out plugs. When were they last changed?