Surging when cold - not AFM or plugs

[Andy_Mac]

Always had a fairly prominant surge when there\'s some load on the engine when cold. Always figured it was just a shot afm but got a replacement which hasn\'t seemed to fix it, car definately feels different but probably just down to resetting the ecu.

Is there any chance its down to the primary turbo? It always seems worst as its getting closer to 0 on the boost gauge. The turbo is pretty whiny so could that being buggered cause a similar effect?

[Rosssub]

When it\'s surging, are the revs rising with the surges? (As though the throttles moving).

Or does just the Boost gauge rise/drop with the surges? (Boost coming on and off).

[D-Style]

Temp Sensor

[Andy_Mac]

Na they\'re not, well not enough to notice.

Na boost gauge stays fairly stagnant. Always around 5-10 inhg. Thought it could be something boost related but as long as the gauge is reading right its below the point that iit\'d be the turbo spooling up enough to make any boost.

Can you assume temp sensor is sweet if the dash gauge starts from cold and goes up to the first line, halfish way up?

Also talking to marky the other day and he mentioned a second temp sensor used for cold starts i think it was. Anyone had problems with that before

[Rosssub]

My original BH5B only has one temp sensor. But I have a version 5 STI pipe here with 2 sensors, the big one for ECU and the smaller one is for the gauge:

My temp sits right on half way, if your on the lower line then yours could be reading low.

If your coolant temp sensor is fluctuating from 70\'-80\', instead of a constant 80\' voltage during normal running. The ECU and O2 sensor will be altering fuelling (cold run/warm run), causing the off boost power surge effect.

[Rosssub]

Looking at the 2 different coolant sensor set ups, the BE/BH single grey coolant sensor has 3 pins. Feed/ECU/Gauge.

The red STI coolant sensor has 2 pins, Feed/ECU. Then the smaller single pin sensor for the gauge. So chances are you need the grey BH 3 pin sensor.

[hijacka]

Try removing the idle control valve and clean it carefully with brake clean also clean the inside chamber where the idle control valve seats. could it be 02 sensor? if its rev a i have a secondhand sensor barely used since new as i switch to link and wideband you could try that?

[Rosssub]

 hijacka said:

Try removing the idle control valve and clean it carefully with brake clean also clean the inside chamber where the idle control valve seats. could it be 02 sensor? if its rev a i have a secondhand sensor barely used since new as i switch to link and wideband you could try that?

Could be O2 sensor (cruising speeds/constant throttle). I would guess the O2 if it was surging when warm? Only doing it when cold or warming up would point to the temp sensor fluctuating below normal temps, so the ECU is constantly switching AFM-Cold run, then AFM/O2 warm run.

[Andy_Mac]

i\'ve cleaned the iacv before, was pretty gunky, didn\'t do the chamber though so should maybe give that a go.

na mines a rev c.

i think o2 is ok seems to be fluctuating as it should.

car was already warmed up when i did this so will have to probably wait until tomorrow to do one from cold.

o2 seems ok to me.

looking at the lean/rich on/off line, would you expect it to be doing nothing when cold and then cycling whilst warm, or would the value still be registered but ignored, would help with rossubs idea if so

https://www.youtube.com/watch?v=9cT3UGipeSo

[Andy_Mac]

and it\'s not normally that warm, had been sitting there running for quite a while

[scottharvey]

This might be my problem my BG does the same thing

[Ben]

My V5 does the same thing. If I start it up, drive down my gravel road at low speed (20-30km/h) I can feel it surging. One minute later completely gone. Hasn\'t worried me enough to do anything about it.

[Guest]

Both mine did it on the stock ecu. Big thread about p2 cars doing it on here and a few others.

[ben-jamminn]

 Ben said:

My V5 does the same thing. If I start it up, drive down my gravel road at low speed (20-30km/h) I can feel it surging. One minute later completely gone. Hasn\'t worried me enough to do anything about it.

My V5 sti is the same, interested to see the outcome of the OP\'s issue.

I\'ve only recently bought the car, so new plugs, upper engine and IACV clean and a new AFM are jobs I all have on the to do list so that may help