Guys, occasionally when I warm start my 2000 XJ, the engine sounds like a tractor, loud, lots of vibration, little higher revs than usual. Then after a few seconds, it returns to a normal idle, as if nothing had happened. Any have a clue what this could be? It was pretty scary the first time it happens, but now I just sit and wait a few seconds, maybe 15 seconds...

thanks in advance

 

Severe piston knock? A little piston knock is totally normal while the engine is cold (Aluminum pistons in an Iron block).

 

It only happens when the engine is warm - and stops suddenly, like an idle valve or something tripped in..

 

Then i'm lost...

 

my 1990 renix would do that, tractor sound .... completly random .. maybe once every 3 months, maybe 6 months

on cold start usually .. I would turn it off asap, as you said, sounds scary & rough

fire it back up & noise was gone, runs fine .. no idea, very curious though

 

injectors heat soak? is it knocking or just rough idle?

 

I had something similar but it was mainly something that sounds like a bad misfire. It was the injector heatsoak and I managed to make it a lot better by getting a couple heat shields over my injectors!

 

What kind of oil filter are you using?

 

Not sure, but I will check - how would the oil filter cause this?

 

Because some filters have a very pour anti-drain back valve (like Fram filters, for example).

This is a great read:
http://minimopar.knizefamily.net/oil...reference.html

 

Thanks for all the replies. I managed to get the hood up whilst it was making the noise, and found it to be the electric fan. Bearings had gone and the fan itself was banging around in its housing. Unbelievable noise for a piece of plastic.