Car hesitating -Lambda?

[bh883]

I have an intermittent problem with my 240 estate which I am hoping someone may be able to shed some light on. My car is a 2ltr K reg fuel injected model. It has done 104,000 miles.

Basically, the car hesitates (sometimes quite violently as though it is going to cut out, other times quite gently). I have had the plugs, leads, caps and dizzy changed but this has not solved the problem. We had an auto electrician have a look at it and his diagnostic machine established that the Lambda sensor was at fault. We have subsequntly replaced this but the hesitation is still there. (Although, it did run perfectly for one and a half days.)

I have noticed that it is more likely to happen after starting (or restarting) the car. This can can be when the engine is cold or it can happen when the car has been running for several miles quite happily but after stopping and restarting the hesitation/misfire is back.

(Having said this, it can start for no apparent reason half way through a journey.)

Sometimes the hesitation clears quickly but other times it will drive you mad for the whole journey.

Any ideas what might be at fault?

Many thanks,

Barrie

[radiomark]

start by looking on the dashboard to see if the Lambda light is on (green and orange triangle warning light).this will tell you if the ECU has logged any fault codes for the lambda sensor or other sensors.
check this and report back.
your car has onboard diagnostics so you can check fault codes yourself without the need for a mechanic.

[bh883]

The Lambda light is on. It came on before we changed the Lambda sensor. I was going to disconnect the battery to turn it off but haven't got round to it.

[radiomark]

disconnect for 5-10 mins then run the car to see if the light comes on.that will tell you you have a fault.
check the 700/900 FAQ in the 700/900 technical section for advice on fault reading and code numbers.

there is a small black box on the nearside wing up by the wiper motor.this is the diagnostic box into which you put the pin,press and hold the button for a few seconds ,then release and the light will flash.count the flashes eg 121. 1 flash, 2 flashes ,1 flash
and check the FAQ for a reference

[bh883]

Thanks for the advice. I have disconnected the battery and given it a very short run and the light has stayed off but, with it being an intermittent fault, I suppose it may take a while for the problem to make itself known.

[Clifford Pope]

Replace the ignition amplifier module - flat plate bolted on the inner wing just in front of the battery. They fail in my experience at about 100,000 miles, usually suddenly but sometimes giving warning in the form of hesitation as you describe.

Other culprits of course are the fuses 4 and 6 for the fuel pumps, and the fuel pump relay.

[bh883]

Thanks. I'll try replacing the the ignition amplifier module. I've checked the fuses and they are fine. This week I have done about 600 miles in the car and it has run perfectly but today it is running like a pig again - very frustrating. The tickover is quite low and very erratic. It rythmically climbs to about 1500rpm and then drops to virtually nothing and keeps repeating the process but it never stalls.

[grass hopper]

this sounds like a MAF sensor problem,need to diagnose the fault codes though.

[bh883]

Unfortunately the Lambda light hasn't come on so I presume the diagnostics thing wouldn't tell us anything at the moment.

[Peter D]

Not all fualts set the EML or record a code. I suspect you have a fualty AMM Air Mass Meter. Disconnect it when it is in hesitation mode. If this stops it then it would point to the AMM. I had a faulty one that reported no error codes but was completely fooling the engine. I was testing the the idel control valve then I dropped a screw driver and it rallted the AMM and hey presto the engine ran fine. I obtained a remanufactured one form a local Bosch specialist and all hes been well since. Regards Peter