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Matt, Mechanical Engineer
Category: UK Car
Satisfied Customers: 21618
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a 2007 mk4 mondeo 2.0 tdci. It starts and runs

Customer Question

I have a 2007 mk4 mondeo 2.0 tdci.
It starts and runs perfect for about 15 seconds then idle becomes lumpy and the engine misfires until it warms up.
I have replace the injectors, egr valve, maf sensor, map sensor and inlet manifold temperature sensor.
Any suggestions as to what is causing the problem.
Submitted: 1 year ago.
Category: UK Car
Expert:  Matt replied 1 year ago.


If the misfire goes away once its warm

This could be a wiring issue as things tend to expand when hot and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;

Airflow meter

Crank position sensor

Cam position sensor

O2 sensor

Throttle pedal position sensor

unplug each in turn and use some switch / contact cleaner spray on the pins to ensure its all grease / dirt free

Also worth checking the connections to the fuel pump for the same reason - unplug each in turn and give them a good squirt of switch / contact cleaner - Not WD40

and also unplug and inspect the main power relays and fuses for signs of overheating or corroded terminals - so the ones for the ECU and the fuel pump

And also unplug the wiring loom connections in the engine bay one at time and inspect for corroded or recessed pins.

Customer: replied 1 year ago.
I have just got a cam position sensor and when I find its location I'll change that.
Expert:  Matt replied 1 year ago.


the sensor plugs into the middle of he head see here

Customer: replied 1 year ago.
Thanks for the reply but the image you sent is for the mk3 which I've already seen and the mk4 is different.Regards,
Expert:  Matt replied 1 year ago.

Hello Ron

Ok on the later engine it should be the more conventional tpye wher its located on the cam cover and the sensor looks like this

Customer: replied 1 year ago.
I already have a new sensor which is different on the mk4 than the image your link is too which is for the mk3.It seems you can't help me with this problem as I'm already aware of everything you have mentioned.Regards,Regards
Expert:  Matt replied 1 year ago.

fair enough

I'll opt out and open this back up to other experts