M104 engine hunting

[MD5]

94 E320 M104 engine, 55k miles.

Returned on a hot day from a longish trip, all motorway, but with traffic jams here and there. Temp crept up in the jams, but didn't overheat (new water pump last year), and returned to normal at speed. Engine started hunting when I put the car into the garage on tickover, so I have started to wonder if this could be the first signs of the loom needing attention, or if it could be something temperature related?

 

[coupe deville]

If it's on the original loom it will deffo need replacing, but it's a rock and a hard place if you delve into it to examine it you will make it worse. Its an expensive fix but could finish up even more so if it shorts and damages the ecu.
The temp on mine never creeps up to nearly overheating, is the fan working as it should ?.

 

[jaymanek]

If its not had the loom, it needs it..

 

[WDB124066]

Could hunting also be related to the MAF, or even the charcoal filter........??

 

[Vlad]

Having had the same problem on 104's I would start off by cleaning the butterfly flap in the throttle body as they get gummed up which then causes the flap to seal incorrectly, thus causing an air leak....this then causes the engine to overfuel and then underfuel and so on...hence the surging feeling that you get.

Very easy to do this yourself. Just make sure that you clean the edges of the butterfly flap by pushing down on it slightly and using a rag around the end of a screwdriver to clean the edges.

If this does not cure it, there is also a large'ish sensor on the nearside wing which has a hose going into it...the sensor has MOT stamped on the top of it. These can get bunged up....which again will cause the engine to overfuel/underfuel. Dead easy to replace.

Hope this helps.

 

[WDB124066]

Got a picture of the sensor by any chance Vlad, be good to know for future reference..........

 

[MD5]

Thanks for the replies. I've owned the car since 40k miles and 6 years, and in that time haven't had the spark plugs changed for fear of disturbing the loom, but have always had a visual check at services, where visual checks are possible, and I know what can lurk underneath. I was actually thinking of replacing the loom next year, and a spark plug change will be due at some point, which will no doubt disturb everything anyway.

On the other hand, my thoughts are that the more heat the loom is subjected to, the quicker the degradation, so mileage may then become relevant, or is that just wrong? I know it's a time bomb, and the car is a keeper/garage queen, so it will get what it needs, beforehand if that is prudent, but I'm trying to understand the symptoms better.

The car normally cruises at just above the 80* marker, but rose to next marker up when stationery in traffic. I haven't used the car since, and will see what happens when I do.

Edit: Thanks Vlad, just read your post, so will have a look.

 

[jaymanek]

you havent changed the plugs in more than 40K miles??? Thats making me cringe...

I would recommend a good soak in wd40 before anyone tried to remove those.

 

[mattc]

JAy
I think he means hes had it since 40K; its now done 55K (i.e 15K difference). still overdue a change (as OP is aware) but not as bad as you thought!

 

[MD5]

you havent changed the plugs in more than 40K miles??? Thats making me cringe...

I would recommend a good soak in wd40 before anyone tried to remove those.

Sorry, Jay, that's senility and too many cars creeping in! I actually had them changed at 48,613 miles, 9th July 09, checking back. I remember the anxiety about disturbing the loom at the time, though, but it was deemed to be good (given the limitations), as it has been the last few services since. There is always a question mark as to what to do on an annual service with the mileage being so low. Ollie has done the last few services, and I'm proud to say he took his lad out in it to demonstrate how a 124 should drive and feel.

 

[Vlad]

Re the loom....if you look at the wires going into the coolant temp sensor near the top hose this will give you a quick indication as to the condition of your loom....if they are cracked at this point then the rest of the loom will be much worse!

Re the sensor on the nearside inner wing.....I dont have a photo, but the sensor is easy to locate as it has MOT stamped on the top.