Engine Performance problem
2002 Kia Rio 4 cyl Front Wheel Drive Manual 114000 miles
For the last 2 years our Kia Rio has had a mysterious intermittent stalling problem which has over time grown worse and is now almost always happening. We have taken it to mechanics and either the problem has not been present during their inspection, or even when present, they just can't seem to find the solution! Worrying!
To describe the engine performance when the car is 'playing up': Once the engine is started you can hear the revs are not uniform. The idle revs can increase and decrease (to the point of stalling) without using the accelerator. As we drive, the engine sounds fragile and will 'chug' at times. The car will often stall when we come to a stop and sometimes as we are slowing down - yes, dangerous in traffic! When driving at higher speeds andthe clutch is engaged the revs will plummet rapidly to near 0. The engine seems to perform a little worse when cold. We can often detect a strong sulphur like smell emmitting from the car when it is performing poorly.
The car has been driven well and regularly serviced since we purchased the car new 6 years ago (no longer in warranty). Recently the battery has been inspected/cleaned, tried a new air filter (sections had been charred?), Cleaning of the throttle body, and computer check indicating no defect & reseting the idle. The mechanics last resort was to replace the IAC valve but with no effect. We have also tried commercial petrol tank cleaning fluids that you add in with fuel (unleaded) to no avail.
We are at wits end with this car but couldn't dream of selling it in it's current state either! Help!
I would have them check the fuel pressure to make sure it is within spec. Also check the exhaust backpressure to rule out a clogged CAT.
I would also have the mechanic hook up a portable scan tool to the car and drive it several miles to try and isolate the problem. They should be able to record live data and anaylize it for sensors out of range.