Idle speed goes lower and second problem

[Guest]

Hi.. I have read a lot of about idle speed motors etc but I have different problem. (Car is EC5A 1997 and ~120 000km driven)

When engine is warm (i have driven at least 10km) and I stop the idle speed lowers from 750-->500rpm. Ecu lift up the idle right away, but it may drop again.
Right after that if I press VERY slowly gas pedal, the car "cuts" (sound from exhaust: "pröt pröt") until I reach like 2000rpm the engine speed jumps right away to 3000rpm (unthought I do not press more pedal)

If I press gas pedal hard it doesn't stall at all.. no "pröt pröt" sound....It takes very fast revs and works totally ok.

I have changed new plugs but no effect.( old plugsphotos: http://harrinkuvat.1g.fi/kuvat/vr4/tulpat/ )
... 3 of plug holes were half away full of oil. I know the oil seals leaks and we opened rocker covers and put some sealing kit to the seals and tightened more covers ( not more that 100km driven after that) And i have ordered new seals too...

Also i changed thermostat because it was leaking inside (seal was broken because it was old) Now engine is 82 degree celsius as it should be.

But those 2 repairs had no effect to that idle and not good engine running while it's warm. Cold engine and the driving is good. No problems then, only at idle at warm engine and after that small "cutting / missfire or stalling".

Is it oxygen sensor failure and idle stepper?
Or ignition coil problem?
Vacuum leak?

Car has 3" cat back exhaust and Forge by-pass valve. Tiptronic car.

 

[bradc]

Is the BOV a vent to air one? If so that may be the problem, or you could have an air leak.

 

[Guest]

Is the BOV a vent to air one? If so that may be the problem, or you could have an air leak.

No, it's recirculate. Not dump valve to air.

Maybe air leak.. but where...hard to find.
Has someone had air leaks and where is it common place to be if it is?

 

[VR4CE]

I had a similar problem back with my 3rd gen magna, under light accel the car would struggle up until 3 or 4000 rpm and make a popping noise, if i floored it the car would be fine

I found the problem to be the o2 sensor, but there was also a problem with AFM, what was happening was because of the faulty o2 sensor the car would backfire through the throttle body under light accel (o2 sensor comes in to play under light accel but is bypassed under full throttle) this was the popping noise, this in turn killed the AFM, the AFM wil only take so many hits, also when this initialy started the onboard diagnostic showed only AFM as faulty not the o2 sensor

 

[Guest]

VR4CE: Did your problem came with idle and after that? Not in drive?
And in warm engine.. cold engine works totally fine.

I have spare used lambda in my garage and i'm going to change it as soon as I have time...

 

[Guest]

Just wondering, does Oxygen Sensor give any fault codes to ecu?

Last days had been worse...no and then car is ok but more and more its like chokes when i press gently gas penal. If I press fast gas penal--> no problems at all...

Had not been time to change oxygen sensor yet....

 

[bradc]

Perhaps O2 sensor then.

 

[Guest]

Perhaps O2 sensor then.

Changed O2 sensor and car works fine now!
Evoscanned also it and no fault codes at all. Works fine and fuel consumption become better.