missfire on ticker

[jaguartvr]

Have a recurring misfire, it only when the car is sitting at tick over. Starts and drives fine but when you stop and the car is ticking over it starts to misfire and the engine light comes on. Pop the scammer on and it comes up with various codes, P300, P302>P306 which mean misfire on various cylinders, different each time. Scan and clear the codes and it is fine until it sits at tick over again. Doesn't happen every time but it's annoying.
Does anyone have any idea what it could be?
Battery did have a fault and kept losing its charge but I have just replaced it and no difference.
I can use the scanner on the port under the steering wheel but can't read anything from the plug under the bonnet, it's a 2000 2.8.

 

[colb]

Check condition of spark plugs clean and gap or put some new ones in. If misfire persists check condition of HT leads if they are originals it might be time to put a new set on. Would expect the coils to be ok as you have multiple misfires on different cylinders.

The OBD2 socket in the car is a slave of the 20 pin round underbonnet socket I would check for bad wiring or dirty contacts on the 20 pin socket if you cant get it to read codes, check out the 20pin to 16pin adapter for bad wiring connections in case thats gone faulty.

 

[jaguartvr]

Can't see a problem with the plugs being reset by the code reader or the plugs causing a problem at tick over only.
Not being able to read from the socket under the bonnet seems to be a problem for early facelift cars. Even a pucker BMW scanner couldn't connect. All pins clean.

 

[colb]

Really sounds like an ignition problem, don't rule out the plugs or the HT leads good move to put some new plugs in then you start with known good working plugs. If that fails to resove the issue move on to the HT leads, replace if they are old and suspect.

My facelift reads codes from both sockets 16pin and 20 pin, the 16 pin will only read the engine module, the 20 pin will read all modules.

 

[andyglym]

Can't see a problem with the plugs being reset by the code reader or the plugs causing a problem at tick over only.
Not being able to read from the socket under the bonnet seems to be a problem for early facelift cars. Even a pucker BMW scanner couldn't connect. All pins clean.

On my C110 scanner it highlights this issue of sometimes not being able to read codes. Can't remember which way round it is but if you turn on the engine and plug in and it doesn't read then plug in when the engine is off and read, of vice versa.

 

[Tfp]

If electrical checks are all good it could be a sticky valve.

 

[t-tony]

I would try an engine flush and oil and filter change.

Tony.

 

[colb]

What model and year is the car and what mileage has it done? If the electrics prove good then I would agree with the others who suggest an engine flush and oil and filter change. Valves can get a build up of varnish on them resulting in sticky operation usually more noticable on start up from cold but quite possibe to manifest itself at tick over if its particulaly bad. Use one of the well known brands of engine flush and follow the instructions that comes with it. Most advise adding it to the engine and running it at full temp for 10 -15 mins then drain and replace oil and filter. Some advise it can be run in the car for no more than 100 miles before draining and replacing oil and filter.

 

[Eddie Zedder]

Had a similar issue with mine once that threw up these codes (plus others). It was caused by the inlet vanos solenoid valve sticking. Simple fix.

 

[jaguartvr]

Had a similar issue with mine once that threw up these codes (plus others). It was caused by the inlet vanos solenoid valve sticking. Simple fix.

Did this happen only on tick over?


Changing oil or plugs is not going to solve the problem as they are not items that can be reset with the code reader.

I was thinking maybe the alternator not putting out enough output on tick over could cause the problem.

 

[colb]

Don't rule out bad plugs or HT Leads they won't set codes but what they cause will set codes such as misfires. Codes set are all well and good to point you in the right direction of a fault such as you have but rarely point you to the issue direct. Always an idea to look upstream of the fault you are seeing as a fault code. Check the induction system for air leaks from airfilter to throttle body and all other rubber pipes on the engine, look for cracks or splits.

If you suspect the alternator simply put a volt meter on the battery terminals and see what its putting out, you should see at least 14.5volts at resonable revs. I doubt this is the problem you have.

You will be surprised in how an engine flush with an oil and filter change will affect the engine particualy if you have a build up of varnish on the valves which can cause sticky operation, a good flush and oil change should put an issue like this to bed.

 

[Delk]

I had the simular problem and it turned out to be a split intake rubber before the throttle body. At idle it was drawing a vacuum leak bypassing the air flow meter causing the engine to run bad. At speed it was fine and I can only guess thats because the amount of airflow was more to overcome the leak.

It idled horribly and threw up the same codes. Fixed the airline and reset the codes and its been fine since.

 

[t-tony]

Did this happen only on tick over?


Changing oil or plugs is not going to solve the problem as they are not items that can be reset with the code reader.

I was thinking maybe the alternator not putting out enough output on tick over could cause the problem.

A code reader registers a misfire only, not the reason for the misfire.

Tony.

 

[jaguartvr]

Mine idles perfectly and also runs perfectly. just occasionally it will start to miss fire if left ticking over.
I will check the intake hoses.

 

[colb]

Good move to check for air leaks before you start throwing money on parts, any rubbers with cracks or splits should be replaced, these engines are very fussy about air leaks. A smoke test would be worth doing if you can't see any obvious cracks or splits just to make sure the system is airtight. If it passes the inspection then start looking at the ignition side plugs and HT Leads. An engine flush and oil and filter change as suggested earlier will also be a good move.

 

[t-tony]

An easier way yo check rubber components is to get an aetosol of carbuettor cleaner and spray the hises etc. while the engine is idling and listen for any change in engine note/speed.

Tony.

 

[g8jka]

Mine has been idling funny on idle for a while but only when cold. Checked a lot of things and clearing the adaptations in INPA gets rid of it completely for a few weeks. Took 4 of the spark plugs out over a month ago now and swapped around the coils to see if any changes. We cleaned the spark plugs up and popped them back in and it's been great 95% of the time. Going to get some new spark plugs soon and try them hopefully they were the issue. But it has also had an engine flush plus oil and filter change recently which may also have helped.

 

[Steve Medlock]

My 2.8 deveolped a misfire on tickover when I accidentally fitted the wrong plugs. Put the old plugs back and the problem disappeared.

 

[jaguartvr]

My battery wasn't great and as the car isn't used daily often went flat. Pop a jump pack on it and it would burst into life and work from the battery so long as it got a decent run. Recently the jump pack wouldn't start it and it had to be put on charge for an hour before it would start, would only last a day or 2. I think one of the cells has failed causing intermittent internal shorting. I have robbed a battery from another car and the missing on tick over has stopped. May well be too soon but I'm hopeful this has cured the problem.

 

[colb]

Now put a volt meter on the battery terminals and check what the alternator is putting out at tickover and with some revs applied you should see at least 14.5volts if its good.