2002 V40 Engine rough until very warm

[acevan]

My 2002 V40 with the 1.9T idles and drives rough for the first 20 minutes or so after starting cold. It doesn't rev freely and vibrations carry though the steering wheel. After it's heated up though, it runs perfectly smoothly. The engine mounts are all brand new, the oil is clean, it had new plugs installed about 8 months ago, and the fuel filter was replaced. I've heard from a couple people that it's likely the coil(s) and/or plugs and/or the spark plug wires. One other people said it might be the crankshaft position sensor. Does anyone have any ideas of where I should start looking?

[t4orce]

I'd be interested to hear from others to see what could fix this. I have a 2000 T4 which I've had since new and for the last 2 years I've had cold start issues like acevan. It even bucks on the engine mounts when it's running rough. Basically it starts fine but the idle is rough and more throttle causes it to want to stall (sometimes it does stall). I normally have to start the car up. Let it idle and sort itself out for 3-5 mins and then drive. If not, it will flatspot and drive horribly.

Here's what my independent Volvo mechanic and I have been through the last week when I've spat the dummy over cold start issues (the car spent an entire week in the workshop to try to fault find).

New spark plugs, coils and leads;
Replaced coolant temp sensor;
Diagnostic readings to check tolerances on injectors, rest fuel pressure, start up fuel pressure, O2 sensors;
Replaced MAF;
Removed air filter;
Trick the computer to think it's cold to dump more fuel

I've spent thousands and have no solution. I've reached a point where I am thinking of selling my car. I've had this baby since new and really don't want to but I'm over it.

[regent]

Each case may be different; the general approach is to look at the fuel trims' behaviour from cold start (the moment System goes into closed loop) till it reaches normal operating temp; also scan for codes - preferably with VIDA

acevan, your case looks like running too lean while cold - could be just a bad ECT sensor, have you ruled that one out?

[t4orce]

I'm starting to wonder if the O2 sensor in my car is the culprit. My mechanics who hooked up the Volvo diagnostic tool said that it is reading but perhaps it is not sending the right signal to the ECU to adjust properly. Might replace that since I've replaced everything else and see what happens.

[regent]

If yours has served for longer than 100k, I say change it as preventive maintenance; the HO2Sensors deteriorate with mileage and gradually become inaccurate.

If you should change it, also make sure to reset the Long-Term Fuel Trims so the sytem will 'learn' sooner. (Just disconnecting the battery and 'pumping' the brake a few times before doing the sensor would clear the LTFT and some minor settings stored in the volatile RAM such as steering angle sensor, window and sunroof, seats, climate control, radio presets, etc. that you may or may not have to redo afterwards.)

[acevan]

I replaced the coolant temperature sensor and thermostat and everything seems to be running fine. Thank you everyone for your help.