poor hot running

[eddieedmo]

Over the last 4 weeks my S2 has developed an intermittent problem when hot.It always runs fine when cold and warming up.If I stop when it is hot it sometimes idles a little unevenly until I blip the throttle and it will settle down.When driving it sometimes hesitates and at other times feels as though it is surging a little.
On full throttle fine.I have replaced within the last 3mths - coil,dis cap & rotor , HT leads,fuel filter plugs all as a matter of routine not because of a problem.It would seem to be a fuel control problem ? FPR ?
All thoughts and ways to diagnose will be welcomed.

Nick []

 

[Lowtimer]

If it's fine on full noise I would suspect some sort of induction leak, possibly a seal or gasket that softens and lets air in when the engine is hot.

 

[Jonny944CS]

Fitting a fuel pressure gauge to the rail should help you diagnose the FPR.

It may also be worth having a good look at the Air Flow Meter. Worn and pitted tracks can lead to poor signals reaching the DME

More here.

 

[eddieedmo]

if it was the AFM would it not also happen when the engine was cold ?
The hose which runs from the AFM over and back under the inlet manifold is very soft could this cause problems ?

Nick []

 

[robwright]

I would say AFM also. They can play up when hot and hesitation could be a sign of a flat spot on the resistor track in the AFM. There is a guide on how to clean the AFM and move the sweep of the arm a clean part of the resistor track in www.clarks-garage.com Also check the throttle position sensor. If it doesn't click in, which can happen when it is hot then the engine will still be running on map and will not switch over to idle defaults. This can cause it to idle high. Mine used to do it and it would go away when I blipped the throttle.

 

[Jonny944CS]

ORIGINAL: eddieedmo

if it was the AFM would it not also happen when the engine was cold ?
The hose which runs from the AFM over and back under the inlet manifold is very soft could this cause problems ?

Nick []

It was your comment that blipping the throttle cured the idle, plus the hesitation/surging issues during running that made me think AFM.
- I agree, logic suggests you should have some issues when cold also - but the AFM is a sensitive sole (different temp AFR etc.).

If it was an air leak, wouldn't the issue only manifest itself with large amounts of manifold vacuum and not clear with a blip of the throttle?

This quick test should help you eliminate the AFM (16v engine specific):

 

[VanhireBoys]

I am going to agree with the boys about the AFM... but a check of the collant temperature sensor is called for as first step..... If you have no problem starting from cold and the car misbehaves when warm that is telling me that the car is over fuelling. The ECU is seeing the engine as cold all the time. If revving the car clears the bad running then it stands to common sense that the cyclinders are flooding and by revving you are clearing the excess fuel......

Maybe I have got it wrong but its no harm to check it and rule it out first..

 

[eddieedmo]

thanks for the pointers , I will check the AFM , how can I test the coolant and/or DME temp sensor ?.Which sensor could be the problem ? Also noticed the hose from the throttle housing which loops through the inlet manifold and back is very soft, should it be like this ?

Nick []

 

[Jonny944CS]

Nick,

To test the engine temperature sensor, connect an ohmmeter between pins 45 and 24 on the DME plug.

Readings should be within the following specs:
0°C = 4400Ω - 6800Ω
15-30°C = 1400Ω -3600Ω
80°C = 250Ω -390Ω
100°C = 160Ω - 21Ω

If the values don't match, connect directly to the two pins on the sensor and try again.