Hi, I recently purchased a Doblo 1.2 with 85,000 miles on the clock. After replacing a faulty coil, it runs great at speed but has a very rough idle. The code is PO300, multiple random misfire. However when I clear the code the car idles ok for about 20 miles of driving then the check engine light comes on again and the rough idle returns. Anybody got any ideas?

It could be a lot of things, as you've just replaced the coil though that is suspect no1, check all connections are solid. check ht leads.
it could also be the crankshaft position sensor which can go intermittent at this mileage.
what you need is an accurate diagnosis tho.

johnhififan said:

It could be a lot of things, as you've just replaced the coil though that is suspect no1, check all connections are solid. check ht leads.
it could also be the crankshaft position sensor which can go intermittent at this mileage.
what you need is an accurate diagnosis tho.

Click to expand...

Thanks Ill check the crankshaft position sensor. Could it be the ECU or computer? Seems a bit strange that clearing the error code fixes it for about 20 miles tho. I notice that the fault always occurs around 1850 revs

Hi,

Any chance that it might be a vacuum leak? The vacuum leak would have a greater effect at lower rpm, and as you increase rpm the leak would reduce its effect on the engine.

John.

sorted it! As it was always happening under load I figured it must be ignition, a bad ECU was on my list but I changed the other coil and all is well now. I guess that if you are replacing one thats obviously bad, it pays to change the other one as well even though there are no obvious shorts etc.