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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.