Engine still coughing and spluttering under load

J

jscpch

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I gave the following info in Jan and recieved some very helpful replies - particularly from 'Television' (Malcolm). Just to recap again - I have a 1994 S280. Last year it began to rapidly increase and decrease revs when in normal tickover. Eventually, after a lot of investigations, the local Merc dealer (not a main agent) changed the plugs, air flow controller and the main engine wiring harness - quite a bill!!
It seemed to cure the problems but then I noticed that when at stop with my foot on the brake (eg traffic lights) the engine began to surge slightly and so I often now slip it out of gear and re-engage when the lights change. I can live with that.
However, I live in an area of France which is as flat as a pancake where the car seems to run very well but, at the moment, I am on holiday in a very mountainous area of Spain and I am finding that the engine is really struggling to go up steep slopes.
It pops, coughs and badly misfire going up steep hills but then runs without problem on the flat or on normal slopes. The steeper the hill the worse the misfire appears to get. Also, if I decelerate then accelerate it also will cough a couple of times then smooth out and run well. There doesn't appear to be any problem if I simply accelerate very hard under normal conditions. It really struggles to get up eg a 1 in 4 (25%) hill
I was advised that the problem was probably due a leak in the vacuum system.
Now, having spent more than 8 hours at three different garages, including a Merc Main Dealer, none have found a leak and I have another new set of plugs and a new exhaust emissions sensor plus bills for about £450 - but I still have the same problem!!
However, a computer check at the Merc agent also indicated a faulty air flow controller even though this was replaced new last year but they wouldn't exchange it under warranty as it was not purchased from a main agent.
But, do the experts out there think that will be the cause of my problems??
I have tried running the car with the connection to the air flow controller disconnected and there appears to be no difference. Help please!
 

television

Always remembered RIP
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Your Mercedes
2002 SL500, 216 CL500, all fully loaded
What make is the MAF fitted to the car
 
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J

jscpch

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Hi Malcolm - it's a Bosch.
One other clue - the car seems to run perfectly when the engine is cold. I took it up some pretty fiercely steep streets a couple of days ago when it was cold but then just did a circuit and it popped and coughed second time round.
Regards,
John
 

television

Always remembered RIP
Joined
Mar 14, 2005
Messages
164,073
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Age
86
Location
Daventry
Your Mercedes
2002 SL500, 216 CL500, all fully loaded
Through some reason your car is running to lean on the mixture, the MAF does set up the mixture, and so does the O2 sensor.

The mapping on the engine would appear to be set wrong, and it needs someone in this line to give an answer
 
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J

jscpch

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Thanks once again. Looks like yet more expense but will wait to see what it is like after the MAF is replaced when I get back to France next week
John
 


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