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Mike, UK Car Mechanic
Category: UK Car
Satisfied Customers: 39198
Experience:  Hi, I am a Car/ vehicle technician of 34 years. 29of -running my own repair/diagnostic business.
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My rx8 is hard to start ( especially when warm/hot ) and sluggish

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My rx8 is hard to start ( especially when warm/hot ) and sluggish compared to when first purchased, I informed Mazda about this on it's last service but no fault was found! I've replaced all the spark plugs to great expence with no improvement. A Mazda technical mechanic told me over the phone that these are signs the cat has collapsed, I did over fill with oil on one occasion but drained after a burning smell from under the car. I wondered if the exhaust system could have excess oil carry over, it appeared extremely hot and sounded like a chip fryer! So, the cat collapsing sounded a likely diagnostic to me. However, the car's second MOT today flew through with no emission problems! The garage mechanic was sure the problem was seals on the rotor, can this be tested and what are my options now?
Hello and Welcome to justanswer....

If the car runs ok when you get it running - its not going to be the cat... and especially as its just passed an emmisions test..

There can be different reasons for this but from what you have described this sounds like an Ect sensor problem... This is the engine coolant sensor - not the one the controls the gauge - but the one that sends signals to the cars Ecu.. main computer - re. the temperature of the engine.

The Ecu then sends commands to the fueling and ignition systems according. If the sensor is faulty and thus sends incorrect , or no info to the ecu as above, the fuel and air mixture will be incorrect and thus do as you describe resulting in poor running and no start situations...

If you remember the old auto and manual choke works like that , only electronically. If and when the choke was in the wrong position for the temp of the engine, the engine either wouldn't start or coughed and spluttered... exactly the same.

This when faulty - rarely shows up as a fault on a diagnostic or a fault code read neither .... Its usually located on the inlet thermostat housing , inlet manifold or thereabouts depending on model and has a two wires pin connector going to it.

Always buy one from a dealer / genuine unit. If you are unsure as to its position - ask the parts dept; when you are in there, to show you on the screen where it is located ....

Too -its a cheap enough part as always worth doing , as they can be so problematic causing all these sorts of troubles..


The other problem with these that comes to mind is with the crank shaft sensor - again - these don't always show up as a fault - but I would go for the ect sensor first in any event....but bear that one one mind...


It may be as well to have the car on a diagnostic machine first - but the sensors as above would be my first choice given your decription of the faults you have.


I Sincerely XXXXX XXXXX have helped you - Please ask me if you need more help...

Kind Rgds, MIKE



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