172 starting problems please help!!

[syski]

hi everyone

i have a 172 on 42K which has just developed starting problems, the engine feels very lumpy when idling. it is idling at around 650rpm and is misfiring a bit, also there is a flat spot until the engine in warm. i have changed the usual suspects air filter element, spark plugs, new stainless steel exhausts system (cat back) as the baffles had gone. i have had 2 dianostic tests from renault specialists but no faults were found!

the funny thing is it runs and performs well the only time it doesnt start is if its left over night however if you turn the ignition on so that the dash lights come on, then turn it off then on again it starts instantly!!

can anyone help me please!!

the only suggestion one garage gave me was it could be a problem with the vvt campulley
timing out ? what do you think?

 

[edde]

I don't think cam timing are to blame you'd have way more trouble (not sure the engine would ever work the valves would mangle up on startup).

Could be the coolent temperature senor there quite comon to fail but usually the problem at high not low temps.

 

[Karl3158]

Possible imobilliser issue, had something similar, would take anywhere between 2 turns of the key and 30 before it would start. TDC sensor may be going, also had that issue that caused a non-starting engine, may explain lumpy engine, TDC (Top Dead Center) sensor monitors piston or cyclinder placement IIRC.

 

[Nomad]

Do 172 have Lambda Sensors? Reason i ask is that my 106rallye had this problem and it was down to the Lambda Sensor, a device which detects the catalyst fumes but can however get dirty. Can't give anymore info i'm afraid...

 

[edde]

If its the imobiliser then the light on the dashboard wouldn't go out.

 

[Karl3158]

172s have either 1 or 2 Lambda sensors depending on age etc..

 

[Karl3158]

If its the imobiliser then the light on the dashboard wouldn't go out.

It will go solid when you turn the key and continue to flash sure, but all other lights will go out.

 

[ant]

sounds pretty normal to me!

 

[RobertCL]

My 172 does this as well. Doesn't always start in the mornings. But is fine at night when coming home from work.

 

[Chris_H]

if it starts fine after you turn it on then off then its a fuel issue, the system won't be holding pressure which is a common thing on these crap in the tank regulator set ups. Further backed up by the fact it only happens when the cars been stodd for a while i.e. overnight.

Turning the ignition on and letting the pump kick in then out then cranking it should net the same result as turning it on then off again.

For future reference.

Immobiliser fault means it won't start at all never mind idle dodgy.

CTS etc again won't stop it running rough then being fine.

TDC sensor if faulty will give a no start situation if it then starts after a no go then if it is the tdc its a dicky connection, chances are the barrel receiver is playing up.

Another thing when cranking an efi car will not just roar into life instantly, first the starter has to crank the engine over at a predetermind threshold speed (normally around 400rpm), it will then activate the injectors and ignition.

 

[syski]

what speed should the 172 idle at? is it normal for this sort of car to run a bit lumpy?
i got the car in winter it seemed to run and start better then.

 

[wrx-172]

Where is the TDC sensor? Anyone got pics?