Can someone point me in the right direction. I have a 2wd Cosworth which starts on the button, no noises, rattling etc. runs fine when giving it a bit of throttle (when stationary, cars off the road at the minute), but as soon as you let of the throttle it stalls. Starts back up fine again. Just stalls once taken foot of throttle.

Is it likely to be the idle valve or tps??

 

First check idle rpm with disconnected Idle valve. Should be minimum 700 rpm.
Adjust with the big copper screw under the throttle body.
Then maybe clean Idle valve.

 

Neither of the above, defo a problem with the base idle which is controlled mechanically with the means of a screw which is located on throttle body, it is secured by a lock nut which needs to be loosened first and if not tightened properly will fall out and so you have no base idle which may be what has happened.

The ISCV job is to raise idle speed ABOVE base idle when desired, nothing else.

Idle should be around 950RPM when hot with ISCV disconnected. If the screw is there try adjusting clockwise to increase idle speed.

Martin

 

As said check base idle first, with all electrics off(apart from engine!!) and iscv disconnected I run at around 900rpm, if no joy and it is a instant cut out when off throttle try turning the tps on the shaft so it "sees" more throttle, when the tps wears it causes the carbon track to have a dead spot, the ecu may interpret this as no fuel needed, hence a dead engine, turning the tps will soon see if it is this problem.
tabetha

 

Ok, I have taxed the car today to give it a run. As stated originally, the car stalls with no throttle. When driving it, seems to hunt between 1000-2000 revs. Ie it will cruise happily at 2000 rpm but then it feels like it gonna stall so you have to give it a little more throttle. When I got back home, the car idled but was dropping to nearly cutting out then reving to 1100rpm then dropping and so on until it eventually cut out.

I tried adjusting the base idle screw when cold, but winding it in made no difference (idle valve disconnected). That fact that it feels like its hesitating when driving too, makes me think TPS. Seems fine when under accleration, and stops hesitating between 1000-2000 when depressing throttle pedal past half way.

gonna try adjusting that over the weekend. Is there anyway of testing it with it disconnected??

 

You never mentioned before about the hunting, now that I know this I would say the TPS is at fault, exactly as said above about the wear spot, this usually shows itself when driving in traffic as well, these are ok when the throttle is above this point as obviously it moves past the worn point.

PF01 TPS is a potentiometer with a switch so with no throttle it is open circuit, it should read around 0.5V at WOT obviously giving a higher valve up until 5V of course the further closed the throttle is. Check between pins 11 and 17.

Easiest way to test is with it still on car, from the ECU connector (You may need an assistant to operate the throttle while you use meter) although is do able by yourself.

Martin

 

Sorry mate, I have just bought the car today and up until today, I have only tested it when cold, standing still. The hunting and light throttle problem, only came to light whilst on the way home. So I check between pins 11 and 17 with the ignition turned on and engine off??

Also, take a look at these pictures... the car doesnt seem to have an amal valve fitted, and the actuator is plumbed straight into the turbo housing. Not sure if this makes a difference to anything ??

 

The actuator plumbing is looking for trouble, there's nothing wrong with the std amal valve.
The addition of hunting tells me it is the CO, it is running very lean by the sounds of it, richen it up to around 2.5 % CO, obviously this needs doing on a gas anylyser, but if it is a car that you don't know the true history of I would suggest that first you replace the coolant temp sensor, this is at the rear of the head on nearside(inlet), a blue sensor with a two pin plug on it, this ensures the fuel mix is correct at the correct temp and is the main corrective factor for fuel mixture.
Just a simple turn of a screw afterwards on the ecu will have it nice and happy!!
tabetha

 

Sounds plausable. It was running a uprated chip, but has had a standard one put back in. Looking at the MOT emissions test, its showing a CO % at idle of 0.13. Im assuming this is very lean??

I have ordered a full sensor kit from MSD so will swap the whole lot next week. I dont have a gas analyser How many turns would see me safe enough to drive it to somewhere to have it setup properly??

thanks

 

As said above ^^ that CO is very low, so it needs adjusting as described above, make sure when you check it on analyzer to make sure the cooling fans are not running as this will give a false reading.

Also as said you need an amal valve as you won't be able to run much boost the way it is at the moment and ECU also has no control over it either!

Looks fairly standard as well which makes a nice change!

Martin

 

Just lay off the boost and it will be fine to drive to the garage, amazing it runs at that!!
Bet it only just scraped through on ppm though, you will be using way more fuel, as it is so lean it won't fully combust, so you will get more power better running and more mpg, can't be bad these days, esp with the price of fuel!!
Let us know how you get on,
tabetha

 

I think the ppm was low too. was around 225 (i think, i will have to double check). I cleaned the idle valve, cleaned the crank sensor which was thick of oil and adjusted the tps slightly too. The result is that it starts fine, ticks over on its own for about 20 seconds then cuts out. Starts again fine, and does the same again. very strange. seems to be doing it on a cycle, ie, if i give it a bit of throttle when its gonna stall, it will tick over fine again for 10 seconds or so then try to stall again....

its getting better, but not quite there

 

Something is not accurate 0.13 and only 225ppm ?
tabetha

 

is it on the correct map sensor?

 

Just checked, got the print out here C0 % 0.13 and HC ppm 252.

Not sure mate, the car was originally setup running around 350 bhp. I have 2 dyno printouts with the car the read about the same. Problem is the car has had some parts removed before i bought it and others left. It has a standard chip in it now, but is still running a T38 with a forge actuator (of unknown spring rate) with no amal or bleed valve. Still has yellow injectors. How can I tell if the map sensor is wrong??

I have got the car running now. I turned the CO screw up a bit and it idles properly now. Started smoking quite heavily at tickover for about 5 mins, smoke all gone now after a 20-30 minute run. I have ordered a sensor kit from yourselves, which im gonna fit this week. Well happy. Seem to have got rid of the oil leaks too.

I will be on the phone soon to have it all setup properly

 

Best thing you can do, take to someone who knows their way around cossies, as it could indeed be a mismatch of bits causing issues as well as other problems.
Mix and match does not work, al needs to be in harmony with each other.
tabetha