Today my cosworth started to idol rough and when you are driving with a little throttle the car seems to run rough but move the throttle a little more and its fine and also on boost is fine too could this be a idol control valve fault or plugs i have checked all hoses and plugs but i i am away from my tools and cant check any further i thought i would ask if any one has had a similar fault cheers

 

I would check the TPS, wear around this point is very common as used the most.
tabetha

 

any one got the details on how to test i.e resistance or voltage checks cheers

 

As said check TPS, you need to check pin 17 (O/P) and pin 11 which is the earth. PF01 (2WD) is open circuit with throttle shut when open slightly it should be 5V this should decrease the more the throttle is opened showing around 0.5V at WOT.

Reverse the about voltages if 4x4 or PF09.

ISCV only operates when cold for air COMPENSATION as richer hence more air needed or heavy electrical load, so certainly won't be this.

Martin

 

At idle speed voltage is 5.0-4.5 volts and at full throttle the voltage drops to 0.5v hope that helps some

 

http://www.cannell.co.uk/Manuals.htm there are full cozi manual on here in pdf you can view or download them. cheers

 

thanks guys i was just on the cosworth manual site there so i have found what i was looking for i will check all sensors tomorrow and let you know if i find the problem thanks again

 

Hi again i have checked all the sensors for resistance and voltage and all seem to be as described in the online diagnostic manual.
The symptoms are when idoling the engine hunts from about 1000rpm to about 500 rpm and back again when pressing the throttle slightly the engine runs rough but when the rpm getts to about 1500 it runs great and on boost is fine aswell. the tps seems to change resistance and voltage smothly the only sensor i found that was near the top of the resistance scale was the map sensor but again the voltage changed smothly when revving the engine all vac hoses seem ok as well all changed about 6 months ago when rebuilt any more ideas would be great

 

hi all i have removed and cleaned up the throttle housing and the iscv and the idle got better but its still a little lumpy when you load the engine i.e. heated front and rear screen on and all lights the volt gage was showing about 12 volts dead with the load does this sound about right or should i expect more i have heard about the alt wiring to battery failing i will check this tomorrow any ideas just let me know thanks

 

is your base idle speed correct, ie warm the car up, unplug the iscv and set the base idle via the screw under the throttle body to 900 rpm.

 

thanks James i was hopping to have done that last night but ran out of time i take it these cars the base idle speed can change quickly as most other threads talk about it this cosworth has been the best runner i have had untill now and funny enugh its running your msd chip, launch,antilang, closed loop and your wasted spark set up i will let you know how the base idle set up helps cheers