Ok, here's the story:

I had to rush up to Sydney (from Canberra) on Friday afternoon for some emergency work at a client. Nothing wrong there, beautiful drive -- on cruise almost the entire way and managed to drop my fuel consumption average from 15.5L to 14.3L.

On Saturday (the day of immense heat), the car was sitting outside the client's premises for a good six hours. When I got back in at around 3:30pm and started it, the entire car started shuddering and it was having a lot of problems just idling. I figured it was the heat and drove off, but the car had less power than a scooter so I got really concerned. Pulled into the first servo I could find ('cos my mobile phone's battery was dead and I needed to find a public phone to call Roadside Assistance). Damn servo I chose didn't have a phone, so I went back to the car.

This time, when I started it, everything was fine and it drove like a dream again. The drive back to Canberra then dropped my fuel consumption average to 13.4L.

So... did the heat cause the shuddering and I shouldn't worry? Or should I worry even though the car seems fine now?

I think it was a heat problem.. i had the same problem in regards to performance.. the XR6 Turbo reminded me of my mirage... it was like it lost so much power it wasnt funny..

Yeah, but remember I don't have a Turbo -- just a normal NA XR6. I figured it would be the heat, but it honestly felt like one of the sparks wasn't firing.

So... did the heat cause the shuddering and I shouldn't worry? Or should I worry even though the car seems fine now?

let your dealer take a look at it...perhaps the on board diagnostics amy show up something :o

Sounds like fuel vaporisation, that leads to vapour locks reducing the fuel supply to the motor, hence rough running, or no running at all.

you had better take it to the dealer if it doesn't idle right at any time, it shouldn't do it wheather its a turbo or not.

by the way I don't think its possible to get vapour lock on a fuel injected car as the pump puts out 300psi. if it vapours at that pressure something is really stange.

You may want to check your engine mounts as well.

Dont think it was the heat mine happened on a cool night the whole motor was vibrating all in the cabin I thought it was fuel but what dirty filter pump and injectors everything is new it felt like it was pre - igniting switched it off restarted it and came good never had a problem since ford wont find a problem like that trust me unless it was dooing it consistantly

This is going to sound very strange, but driving in the heat on Saturday my XR6T has never ran so good. Traction control come on from a standing start first time ever... It felt much quicker (but I have changed the fuel to Optimax, and it was the first good run after a weak of short city only trips... )

With all the other crises in Canberra atm, I'm going to wait until my 3000km check-up and definitely mention it there, unless it does it again -- in which case, its straight to the dealer!