Hunting idle RPM - Page 4

Paul Newell · Mar 25th, 2013, 12:05

Thanks classicswede

A mate of mine is a rather cleaver car man and his first diagnosis is the same as yours: needs a longer run so that the ECU can reset itself. That will happen this evening.

He also suggests squirting some carb cleaner down the air intake to: 1) clean the mass airflow and 2) clean the jets. As the car has 138,000 on the clock and has not had this done since I bought it, 50,000 miles ago, I don't think it would do any harm.

The car is only petrol by the way. I've never thought about converting to LPG as my cars are alway bought with relatively high milage and I tend to drive them into the ground (they all rust out, never with and engine problem) so have never thought the investment worth while.

I'll post again when I've done the above suggestions and report what happened.

Paul Newell · Mar 25th, 2013, 18:22

Hi again

Sprayed the carb cleaner and the hunting more or less stopped.

Just done an extended run and it's much worse than I thought.

Apart from oil being forced out of the oil filler cap the engine smokes horribly when accelerating after deceleration.

It looks like either valve seals or broken rings. Whichever one it is it's going to cost a fortune. Something I don't have at the moment.

Anyone with any suggestions?

capt jack · Mar 25th, 2013, 20:41

Oil being forced out of the filler cap could be a blocked PCV.There's a little filter where the PCV system goes back into the throttle body, and this can/should be removed altogether.

You can quite easily confirm piston ring or valve damage with a compression test.

The spark plugs may be new, but what about the leads, distributor cap and rotor? If the crankcase pressure is too high then oil could be forced past the camshaft seal and into the distributor, and that would cause rough running.

There are all sorts of possibilities with this.

I'd recommend getting down to the basics before assuming the worst. Start by removing, cleaning and re-gapping the plugs (the state of these will give a clue as the condition of the engine too), clean and inspect all the plug leads. Remove and clean up the dissy cap and rotor. Have a look at the air filter and see if it's reasonably clean and clear. Remove and clean the throttle body. All this things cost nothing to do, only time.

These engines are well built, tough and long-lived. 138,000 is not a high mileage. It could be that there's a big problem of course, but on the balance of probabilities it's more likely to be something ignition-related and simple to fix.

Cheers

Jack

PS: I think that your car is more likely to have a MAP (manifold absolute pressure) and inlet temp sensor data from which is used to calculate optimum fuel mix, and not a MAF (mass airflow) sensor.

classicswede · Mar 25th, 2013, 22:17

And if it is the Map sensor engine high a blocked breather pipe would help explain the scewed running.

Paul Newell · Mar 26th, 2013, 11:53

Hi again
Thanks for the advice about blocked tubes. I'll have a look.

My tame car expert says that there is a slight oil film over the bottom of the air filter indicating that there is some unwanted pressure in the system. He thinks this might have been happening for a while.

The pressure build-up under the oil filler cap is quite rapid even at tick-over.

The sump oil is still quite clean having done over 4,000 miles since the last change (it's never dirty even at 10,000 when I normal change it) so I think I might be able to rule out a problem with the pistons but I'll still run a compression test just to make sure.

The engine uses about 2lts of oil between changes. I'm not sure if that is usual or not.

I'm not getting any smoke out of the filler cap nor am I getting any water into the cooling system which would appear to rule out a head gasket problem.

I agree with the thoughts about the engine being tough. Mine is at the bottom of the horse power range at 170bhp with no turbo. I've always felt that, even at high speed, the engine was never struggling to get there or to stay there.

If anyone has any more advice then I'm all ears and thank you for the advice so far. I appreciate the time you have spent with your replies.

Mar 25th, 2013, 22:17	#34
classicswede Trader Volvo in my veins Last Online: Yesterday 21:48 Join Date: Dec 2004 Location: Anglesey	And if it is the Map sensor engine high a blocked breather pipe would help explain the scewed running. __________________ http://www.classicswede.org www.classicswede.co.uk

Mar 26th, 2013, 11:53	#35
Paul Newell New Member Last Online: Dec 17th, 2017 01:40 Join Date: Mar 2013 Location: Bembridge	Hi again Thanks for the advice about blocked tubes. I'll have a look. My tame car expert says that there is a slight oil film over the bottom of the air filter indicating that there is some unwanted pressure in the system. He thinks this might have been happening for a while. The pressure build-up under the oil filler cap is quite rapid even at tick-over. The sump oil is still quite clean having done over 4,000 miles since the last change (it's never dirty even at 10,000 when I normal change it) so I think I might be able to rule out a problem with the pistons but I'll still run a compression test just to make sure. The engine uses about 2lts of oil between changes. I'm not sure if that is usual or not. I'm not getting any smoke out of the filler cap nor am I getting any water into the cooling system which would appear to rule out a head gasket problem. I agree with the thoughts about the engine being tough. Mine is at the bottom of the horse power range at 170bhp with no turbo. I've always felt that, even at high speed, the engine was never struggling to get there or to stay there. If anyone has any more advice then I'm all ears and thank you for the advice so far. I appreciate the time you have spent with your replies. Last edited by Paul Newell; Mar 26th, 2013 at 11:55. Reason: spelling mistakes.

Mar 25th, 2013, 12:05	#31
Paul Newell New Member Last Online: Dec 17th, 2017 01:40 Join Date: Mar 2013 Location: Bembridge	Thanks classicswede A mate of mine is a rather cleaver car man and his first diagnosis is the same as yours: needs a longer run so that the ECU can reset itself. That will happen this evening. He also suggests squirting some carb cleaner down the air intake to: 1) clean the mass airflow and 2) clean the jets. As the car has 138,000 on the clock and has not had this done since I bought it, 50,000 miles ago, I don't think it would do any harm. The car is only petrol by the way. I've never thought about converting to LPG as my cars are alway bought with relatively high milage and I tend to drive them into the ground (they all rust out, never with and engine problem) so have never thought the investment worth while. I'll post again when I've done the above suggestions and report what happened.

Mar 25th, 2013, 18:22	#32
Paul Newell New Member Last Online: Dec 17th, 2017 01:40 Join Date: Mar 2013 Location: Bembridge	Hi again Sprayed the carb cleaner and the hunting more or less stopped. Just done an extended run and it's much worse than I thought. Apart from oil being forced out of the oil filler cap the engine smokes horribly when accelerating after deceleration. It looks like either valve seals or broken rings. Whichever one it is it's going to cost a fortune. Something I don't have at the moment. Anyone with any suggestions?

Mar 25th, 2013, 20:41	#33
capt jack VOC Member Last Online: Yesterday 21:22 Join Date: Jun 2006 Location: Selby, North Yorkshire	Oil being forced out of the filler cap could be a blocked PCV.There's a little filter where the PCV system goes back into the throttle body, and this can/should be removed altogether. You can quite easily confirm piston ring or valve damage with a compression test. The spark plugs may be new, but what about the leads, distributor cap and rotor? If the crankcase pressure is too high then oil could be forced past the camshaft seal and into the distributor, and that would cause rough running. There are all sorts of possibilities with this. I'd recommend getting down to the basics before assuming the worst. Start by removing, cleaning and re-gapping the plugs (the state of these will give a clue as the condition of the engine too), clean and inspect all the plug leads. Remove and clean up the dissy cap and rotor. Have a look at the air filter and see if it's reasonably clean and clear. Remove and clean the throttle body. All this things cost nothing to do, only time. These engines are well built, tough and long-lived. 138,000 is not a high mileage. It could be that there's a big problem of course, but on the balance of probabilities it's more likely to be something ignition-related and simple to fix. Cheers Jack PS: I think that your car is more likely to have a MAP (manifold absolute pressure) and inlet temp sensor data from which is used to calculate optimum fuel mix, and not a MAF (mass airflow) sensor.

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