740 brakes affecting idle?

['88740GL]

hello all,

I've noticed that when my car is cold it will idle up and down at 500 rpm and 'chug' once warmed up it will run perfect...however i've noticed if i pump the brake pedal quickly on idle that same chugging returns and i assume when brake vacuum rebuilds again, the idle smooths out once again.....should there be a non return valve on the vacuum pipe between the manifold and the master cylinder?

[OldBlueVolvo]

Originally Posted by '88740GL

hello all,

I've noticed that when my car is cold it will idle up and down at 500 rpm and 'chug' once warmed up it will run perfect...however i've noticed if i pump the brake pedal quickly on idle that same chugging returns and i assume when brake vacuum rebuilds again, the idle smooths out once again.....should there be a non return valve on the vacuum pipe between the manifold and the master cylinder?

Yes, there is a check valve at the end of the brake booster hose.

[grass hopper]

Originally Posted by OldBlueVolvo

Yes, there is a check valve at the end of the brake booster hose.

to check the one way valve for the servo, - run the engine then switch of,then after 10 seconds apply the footbrake and it should feel normal for approx 3 applications then the brake pedal will go hard until the engine is started,if the valve is faulty the pedal will be hard straight away.never had one valve fail in many years,standard issue the engine hunting if the brake pedal is pressed hard and released quickly.

there is a cold start problem with the car,dependant on engine variant.

['88740GL]

Thank you guys, i checked and the vacuum is still there after the engine is turned off, even when left sitting over night so we know its not the check valve in this case...

the engine is the 'B200E' (2.0 , continuous injection, with no catalytic converter, it runs on lead replacement petrol, but would be nice if i could get hold of real leaded fuel.

I've noticed theres no 'engine light' does that mean theres no onboard diagnostics or fuel injection computer, or is this a purely mechanical system?

Sorry for so many questions, this is my first volvo :-)

[NI_Volvo_Nut]

Fairly normal for slightly rough idle when cold on these engines, any hot start issues?
No electronics for the injection on these engines, other than the cold start injector.

[timofthomas]

hi fella - my B200e runs very happily on unleaded with no problems - Volvos were designed for Unleaded very early on so highly likely you can use premium unleaded - though of course they do prefer to run on the higher octane stuff and mine runs a lot happier on v-power - no issues other than that. Might save you a pretty penny and be easier to get hold of....

[grass hopper]

first thing I would do is change the injector seals as these tend to leak and draw air causing poor idle,then the co will need adjusting after.

['88740GL]

Originally Posted by NI_Volvo_Nut

Fairly normal for slightly rough idle when cold on these engines, any hot start issues?
No electronics for the injection on these engines, other than the cold start injector.

No hot start issues whatsoever....its a bit of a strange one..... i'm now suspecting the idle air control valve...(auxillary air valve)

['88740GL]

Originally Posted by grass hopper

first thing I would do is change the injector seals as these tend to leak and draw air causing poor idle,then the co will need adjusting after.

Are these easy to do? i mean i'm generally a little knowledgeable of cars, i change oil, filters and plugs, glow plugs, bulbs etc, most easily manageable tasks. Where can i get injector seal kits from?

['88740GL]

Originally Posted by timofthomas

hi fella - my B200e runs very happily on unleaded with no problems - Volvos were designed for Unleaded very early on so highly likely you can use premium unleaded - though of course they do prefer to run on the higher octane stuff and mine runs a lot happier on v-power - no issues other than that. Might save you a pretty penny and be easier to get hold of....

Ah, right, i just been using castrols valvemaster lead replacement as it says in the handbook that 4 star 98 RON fuel is needed and in the haynes manual that unleaded should not be used, my car has no catalytic converter, so thats why i've been using lead replacement in it, just scared of pinging and valveseat recession.