1994 320 SL hunting on tickover

[Dyno Des]

Has anyone come across this problem ? My sl auto runs fine apart from when ticking over in gear. The engine begins to hunt., gradually getting worse untill you can hardly hold it on the brakes and it's even worse in reverse.
The brakes are rubbish which I believe is related to the hunting problem.

I initialy diagnosed a vacume leak but NONE are present. I then checked to see if there was an internal leak in the brake servo diaphram. I disconnected the servo vacume pipe and blanked it off, result, still hunting.

I then disconected the mass airflow meter, result, still hunting.
I then had it code read, no current faults shown. 1 stored fault, lambda scensor at rich stop, weak mixture. pulled the lambda scensor, blew off the soot with the air line, refitted it, result, still hunting.

Took the car for an emmisions test, lambda reading perfect, CO perfect, HC perfect, result, still hunting

I need to get this sorted, as the wife won't drive it and she needs to go to Tesco on Friday ! Any help would be much appreciated,

thanks, Des

 

[television]

Welcome to the forum Des.

Hunting is an air leak normally. Are the headlamp raising OK, if the brakes are bad, in what way, excessive pressure on the pedal or what ?

All vacuum tubes on the inlet must be a good fit, could be inlet manifold gasket.

 

[MercStraight6]

The Lambda may still be faulty; I had the same code and replaced the Lambda and it improved things greatly.

 

[Number_Cruncher]

Check the voltage output of the lambda sensor - it shouls sweep between 0.2 and 0.8 volts about once per second at tick over, getting faster if you rev up a bit.

 

[kth286]

Des

Have you got a small electrical regeneration valve on the NS inner wing ???

It has two pipes going to it and is marked with MOT on the top of it.

When the engine is up to full operating temperature and has been running for at least two minutes, does it pulse ??

You should be able to both feel it and hear it pulsing.

If it is not pulsing then it may have stuck in open position and allowing petrol vapours into engine at inappropriate times.

 

[Dyno Des]

Thanks Guys,
I will check out your suggestions and let you know the results,
cheers, Des

 

[Dyno Des]

Hunting problem cured, thanks to everyone who posted.
The winning answer was kth 286. Underneath a large plastic shield on the ns inner wing a valve with m.o.t. on with one vacume pipe atached and one vacume pipe hanging out !
Result happiness. Thanks, David

Brakes still a bit rubbish, like poor servo efficiency, also got a wirring noise somewhere inside the car, wife says it's like a helicopter hovering, any ideas,

cheers, Des

 

[rpe2]

Does it change frequency with the fan heater?

 

[Dyno Des]

No change with heater fan but does become more noticeable when braking,

Des