Mis-fires on this engine are in the main caused by a faulty ignition module which when replaced more often than not cures the problem.
However I have today 09/09/2016 received this e-mail from Stefan in Bulgaria, I will copy the complete e-mail which mail help owners with persistent mis-fire problems:-
Hi. I have a small garage and a friend of mine came with 1998 A160 working on 3 cylinders. Diagnostics said that Cyl 4 misfires.
Strange thing was that engine works very well after start.
No matter hot or cold. No misfires at all, smooth idle.
If you press gas pedal and rev the engine past 2000 rpm misfire code appears and ECU shuts down cyl 4.
I struggled with that problem all day. Finally removed valve cover and saw a broken spring of the intake valve (picture included). Managed to replace it without removing the head...
I searched WWW for help and found your site. It is great and will be a lot of help to many people. So if You decide share this info: these engines are getting older and it will eventually happen to other cars
Cheers and keep going
Greetings from Bulgaria
Stefan
Many thanks Stefan, I have already passed your e-mail on to John in Australia who is suffering a similar problem, who knows it may also point him in the right direction .
Lofty
This is the unique shaped engine that is fitted into the W168 model 'A' Class, although it has advantages from the safety point of view, its layout has disadvantages when maintenance on the engine has to be carried out, even replacement of such things as a starter motor are very expensive when compared to other modern cars as the engine has to be at the very least dropped, If starter ring gear is damaged ,then the engine would need to be totally removed. It would be nice to think that having bought a 'Mercedes-Benz' the maintenance levels on such items as starters would be more remote , sadly that is not the case and running costs when taking into account that the car's ASSYST maintenance program calls for a service every twelve months at an average cost of £350 can make it an expensive car to run.
Both the engine and gearbox are mounted on the front sub frame. In the event of their necessary removal, for such items as clutch replacement, gearbox defects they have to be removed completely from the raised vehicle. For such items as starter motors, oil level sensors, and poly 'V' belt tensioner the engine /gearbox unit can be lowered, albeit space is still tight for working.
In both instances this is done by lowering the combined engine /gearbox unit on the front sub frame from the raised car. A Indicates the front of the frame.
This cut-away needs no introduction although I
find it quite frightening to see the sophistication and layout of this power pack.
This shot of the off-side of the engine gives a splendid view of the pulley's and the 'V' Belt which is partially removed. This was obviously done when the Air Conditioning compressor was removed from the engine at point A If the compressor is removed for any reason with the system charged with refrigerant gas, then take extreme precautions to ensure that undue stress is not placed on the flexible or rigid tubing leading to and from the compressor, a photo of which is inset.
Well thanks to Luko in Brazil we now have a complete engine which is still mounted on the sub frame complete with suspension units and hubs, along with the power steering reservoir and motor below. I doubt luko will recognize it, he had the misfortune of getting water into his automatic gearbox which meant stripping out the whole engine and then stripping and re-building the gear box, due to corrosion of a valve. Luko's advise to all owners of 'A' Class with automatic gearboxes is to ensure they are using a coolant with a anti-corrosion inhibitor in it. Stick with the MB recommended coolant and change it at the prescribed intervals and you are less likely to face the bill that followed Luko's repair. Cost of Luko's repair £2500 approx and you could add at least another £1000.00 in to that the UK If you could find an MB garage who were competent to do the job, you might find a fitter who would fit a new gearbox. I leave you to make enquiries re the cost, I don't want to endanger your health!
Engine Problems
Generally speaking this engine does not give problems .
The ECU combined air mass sensor can be a problem but if you read the information on my page 38 even this is not such a problem as it can be unless you insist on using the services Mercedes Benz when you will find this repair to be very costly indeed.
Timing chain defects and breakage have been reported on the A140 but few problems to my knowledge arise on the A160.
However one fault has just arisen,12/5/10 for the first time to my knowledge where an A140 W reg 51,000 miles suffered severe problems with the tappets.
According to the owner this problem arose almost overnight with a severe tapping. I asked the question did the noise come on gradually? the answer was as follows:- Almost over night, the engine did make some noise but not at a level where
you would notice it. When the tapping started, everyone commented on the
noise which was like two ball bearings hitting together is synchronisation with the
engine speed.
Following the owner's further investigation the tappets were found to failed and had to be replaced.
The owner was able to replace these himself but you do not need just a good working knowledge of the
combustion engine but a good range of tools as well, and this car does call for 'Torx' sockets which aren't readily available in every toolbox.
Most important is to ensure that all components are marked before removal even to the direction they face, and that all components are replaced precisely as removed.
Ensuring the engine, No 1 pot/piston is at Top Dead Centre (DTC) (normally firing order 1,3,4,2 and no 1 piston is nearest the timing chain.) also ensures that you can confirm things are as removed when the job is completed. Securing the timing chain to the cam shaft pulley wheel with electrical ties is another way of ensuring the return as found.
The Degree of difficulty is dependant upon your knowledge of engines, if you fully understand the concept of top dead centre & basic understanding of workings of an engine, then the rest is just removing bit and putting them back. I find that taking digital photographs as you progress is also helpful if you want a reminder as to how precisely a component was fitted or situated, and remember to double check that you re-connect all wires and hoses on completion or you may cause yourself yet more anxiety trying to find out why something does not work or why a warning light is showing. Chris, the owner of this vehicle had already replaced the timing chain tensioner which is known to be a problem on some early A140s before having to look further due the tensioner not curing the problem, however his time and money was not wasted in this respect, as a timing chain quickly wears if it is not correctly tensioned which in the longer term can result in breakage. This invariably damages the engine to such a degree that it needs replacement at great cost due to bent valves stems and alike.
Although this owner was able to source some parts from 'Europarts' always use you vehicles Vin to ensure correct fit & function.
Costs involved 12.05.2010
Repair cost £168 inc vat, Europarts tappets set of 8 £57.00, Europarts 'Torx'(star) Socket Set £7.00,
Mercedes Timing chain tensioner £74.00, Mercedes Rocker box gasket £12.00, Halfords 'Torx'(Star)socket £4.45
Remember if you are unfortunate enough to suffer this problem, then before removing small components plug all recesses or holes with cloth to prevent accidental loss of nuts screws etc, the last thing you want is to turn a difficult job into an impossible one, remember and ensure everything is removed on completion.
This drawing shows the location of the Alternator and where fitted the compressor for the air conditioning.
This photograph from the rear shows us where the starter motor A and solenoid are located in relation to the engine.
Did you ever see anything like it? An 'A' Class engine! Looks more like something out of a Garden Centre! But worth considerably more. You will appreciate that the engine is incomplete, less Air filter housing and EMS housing, it has been stripped and removed from Luko's car in Brazil from major overhaul of the gearbox. However the throttle body can still be seen attached to the left hand side of the engine
Thank you luko for allowing me to add your photographs to my site. For more pics and details go to baby-benz.com Tec forum. 5/09/05
1.
Air filter housing
2
EMS location
3
Oil Dip stick
.4
Oil filter housing
5
Pulley 'V' Belt
6
Alternator & Air Con pump location.
7
Inlet manifold
8
Flywheel.
I'll leave you the reader to decide what this lot is? Glad it is not my engine!
In fact it is two engines from which the gearboxes have been removed, what we are looking at is the flywheel from which the thrust plate and clutch assembly have been removed.
Mis-fires on this engine are in the main caused by a faulty ignition module which when replaced more often than not cures the problem.
This is the unique shaped engine that is fitted into the W168 model 'A' Class, although it has advantages from the safety point of view, its layout has disadvantages when maintenance on the engine has to be carried out, even replacement of such things as a starter motor are very expensive when compared to other modern cars as the engine has to be at the very least dropped, If starter ring gear is damaged ,then the engine would need to be totally removed. 
Both the engine and gearbox are mounted on the front sub frame. In the event of their necessary removal, for such items as clutch replacement, gearbox defects they have to be removed completely from the raised vehicle. For such items as starter motors, oil level sensors, and poly 'V' belt tensioner the engine /gearbox unit can be lowered, albeit space is still tight for working.
In both instances this is done by lowering the combined engine /gearbox unit on the front sub frame from the raised car. A Indicates the front of the frame.
