As title, the car starts and idles perfectly from cold then as it warms up the revs start hunting and occasionally when rolling to a stop the revs will drop completely and cut out, also I have a slight hesitation between 2-3k revs and in 2nd and 3rd gear, please help It is driving me mad, I am running my new motor in and am worried this will not be doing it any good, Thanks! Kurt

 

Probably should have said the car is a V4 type R running mafless

 

I would have said it's the maf, but then you posted that you don't have one, so now we're into idle control valve and 02 sensor territory.

Who did the build? remove and re-fit?
did you go for a running in map?
any other parts changed?

 

MAT sensor giving you grief maybe - could it be coated in gunk and needing a clean?

 

Changed the front o2 sensor and cleaned the idle control valve etc. I have replaced the standard inlet hose onto the idle control valve with a full silicone one but Duncan(racedynamix) said this would be fine

It was doing the same thing before the build, I'm not on a running in map no. cheers

 

is it because the engine heats up or because the engine bay heats up. Check MAT sensor incase it's not reading properly.

 

Do you mean the MAP sensor? If so I have cleaned that out and wasn't gunked up either

 

nope - MAT sensor, manifold air temp - you should have one somewhere for speed density as air temp changes the oxygen amount if it's loose/leaky/heatsoaking/broken/not actually connected to the manifold then you will have an issue as it's temperature changes. Suddenly the ECU thinks there is X amount of air when really there is Y amount of air.

 

What about the IAT sensor? Mine is just hanging loose at the front of the car, could this be the problem?

 

IAT could be used instead of MAT - depends who set the car up for speed density.

 

I would have thought MAT and IAT are one and the same.

If your IAT sensor is hanging down the front of the engine then of course you'll have issues, why is it out?

V4 car, are you using ESL?

 

Similar yes, but not the same. Manifold Air is going to be post intercooler, Intake Air is pre intercooler fair bit of difference when you look at higher boost pressure and outside air variance.

Are you sure the sensor hanging at the front isn't just for the dash temp and not the actual ecu sensor?

 

Makes sense when you think of it that way. I've always seen them referred to as IAT sensors, even in the ESL manual. My IAT sensor is post intercooler and just at the opening for the throttle body, it's an add on for ESL if I want to go MAFless.

 

And a much better place to have it than at the intake if your going mafless/speed density setup full time.

 

I just brazed a new boss to my intercooler pipework and fitted a sensor just in case, not really convinced I need it but it's there if I do. Might go MAFless when I fit the TD05 and injectors.

Anyway, back to the post. If the OP has in fact got the IAT sensor dangling around then surely this is the issue. Do the V4 cars have dash temp displays?