4AGE 20V hesitating when cold

[onnaj]

Hello,

Since a few weeks my 4AGE 20V Blacktop hestitates when cold. The first, let's say about 5 minutes, it struggle to climb in rpm like all torque is gone. After that it runs fine. Any ideas about a possible cuase?

This is what i've done thus far:
1) New rotor, distributor cap, plugs and cables (only 9000 km old)
2) Checked the timing with a timing light and it's about 8-9 BTDC
3) Measured the resistance of the primary and secondary coil and it's perfect
4) measured the o2 sensor and that's also perfect
5) measured the distributor and it's good also (didn't measure the gap between the rotor and the contacts yet)
6) Installed a new battery while i had the idea the old one was a bit bad
7) Changed from my Ramair filter to a NEW genuine Apexi filter, seems to make it a bit worse
8) Balanced the itb's past year
9) Engine was completey rebuild about 10k km ago with new pistons, bearings, valve grinding, valve adjustment, new oil pump, water pump all new gaskets etc etc

I'm out of clues. Only thing i could think about is either (one of) the injectors, fuelp pump or fuel pressure regulator. Any idea how to test those?

This is how the spark plugs look (after 10k). I took them out after a short ride. I don't think they look too bad, maybe a bit too much carbon, which might be a sign of running a bit lean. On the dyno (about 7.000 km ago my A/F was just perfect (between 0.85 and 0.9) at full throttle.

[BLK_20v]

Faulty sensor on the water temp to the ecu...

[jondee86]

Possible Causes of Engine Hesitation or Stumble:

* Dirty fuel injectors
* Bad MAP (manifold absolute pressure) sensor
* Bad TPS (throttle position) sensor
* Bad or dirty MAF (mass airflow) sensor
* Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
* Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
* Bad gasoline (fuel contaminated with water or too much alcohol)

These are some causes of "lean stumble" plucked from a random site.Basically it is too much air or not enough fuel causing the mixture to be leaner than design when the engine is cold. The fact that you feel the stumble became worse when you installed a freer flowing filter, tends to confirm this hypothesis

Cheers... jondee86

[DX20VT]

do you run a catch can? or is it standard?

[onnaj]

do you run a catch can? or is it standard?

Nope i have the stock setup with only an Apexi open air as a mod.

[DX20VT]

Try removing the breathers from the tappet cover to the intake, you will need to block the one with the PCV valve in it to the manifold end,
and see if it makes a difference.

Does your car use oil?
(Sorry, it's a 20V they all do)

[onnaj]

Try removing the breathers from the tappet cover to the intake, you will need to block the one with the PCV valve in it to the manifold end,
and see if it makes a difference.

Does your car use oil?
(Sorry, it's a 20V they all do)

Okay i'll try that.

The car uses not much oil, i guess about 0,5 litre on 5000 km with Shell Ultra Helix 5W40. Most oil is leaking through the distributor housing, so i'm going to try to rebuild that soon. Before i had 5W30 and it was using a tad more on that, but the engine was rebuild only 10k km ago so in the beginning they oil use extra oil in the break in.

[BLK_20v]

Don't do that unless u want blow by

[DX20VT]

Don't do that unless u want blow by

Don't do it permanently,

but do it for a day or two to see if it fixes the problem.

If it does than you need to look at a catch can option or something..

[BLK_20v]

Shake the pcv valve and make sure the little ball rattles... When cold hesitation i've always found to be either the start signal not connected to the ecu (only on conversions)

or a faulty ecu temp sender.. 2 wire plug on the side of the block near the heater hoses.