2008 Mazda 3 nearly stalling at idle

The_Nipper_One

Hey guys, would really appreciate if someone could help out with this.

I'm driving a 2008 mazda 3 1.6 petrol which has 63,000km on it.
For the past few months it will very occasionally nearly stall when idling.

To give a complete run down of what happens:

The car will usually idle at approx 800revs, but for some unknown reason it will occasionally drop to about 200-400 revs, and the car will shake as if it is about to stall before returning to normal. This all happens over the space of about 2 seconds with 0 input from me (Car is out of gear, handbrake on, I'm just sitting there in a car park for example watching it happen).

I don't know how to reproduce this at will, it just seems to happen at random.

jimgoose

Is this inclined to happen after you rev the engine a little and then lift off the accelerator? Could be running rich, due to some sort of a sensor problem. It would be useful to read any OBD code that might be logged.

The_Nipper_One

jimgoose wrote: »

Is this inclined to happen after you rev the engine a little and then lift off the accelerator? Could be running rich, due to some sort of a sensor problem. It would be useful to read any OBD code that might be logged.

It doesn't seem to do it after a rev.

However, I nearly always notice it happening after a short drive, for instance when giving someone a lift to a local shop and I'm waiting for them in the car park with the car ticking over.

jimgoose

The_Nipper_One wrote: »

It doesn't seem to do it after a rev.

However, I nearly always notice it happening after a short drive, for instance when giving someone a lift to a local shop and I'm waiting for them in the car park with the car ticking over.

Yeah. As I said, probably one of the sensors - possibly the coolant temperature sender, giving a false reading and keeping it on the cold-start enrichment table after warm-up? You'll need to have it checked out by a garage.

The_Nipper_One

jimgoose wrote: »

Yeah. As I said, probably one of the sensors - possibly the coolant temperature sender, giving a false reading and keeping it on the cold-start enrichment table after warm-up? You'll need to have it checked out by a garage.

I looked up some of the symptoms of a failing coolant temperature sender.

Difficultly starting after engine has reached normal operating temperature,
black smoke from exhaust,
overheating engine.

I have none of these symptoms, though just to make sure, the next time I'm in the car ill try and start it again after it has warmed up fully.

jimgoose

The_Nipper_One wrote: »

I looked up some of the symptoms of a failing coolant temperature sender.

Difficultly starting after engine has reached normal operating temperature,
black smoke from exhaust,
overheating engine.

I have none of these symptoms, though just to make sure, the next time I'm in the car ill try and start it again after it has warmed up fully.

That was merely an example, there are a couple of sensors in there that can cause idle problems, including the MAF, CTS, idle-control solenoid, even a failing battery. And being pieces of hardware they invent new and interesting failure modes every week.

The_Nipper_One

Looks like it will just need a trip to a garage then , though I think I'll try and figure out how to reproduce the problem before I take it.

Thanks for your help.
Any idea how much a problem like this will cost to fix? Assuming it is a sensor of course.
(This is the first car I've driven, never had to take one to a garage before)

88manta

What county is the car in?

You'll need to get someone with dealer level.diagnostic equipment to scan for fault codes.

Cheapest and quickest way in pinpointing the problem

The_Nipper_One

Car is in Laois 88manta

88manta

Hopefully someone in the vicinity will get in touch with you!!

Diagnostic scan will point you in the right direction.

Maztech

From my experience with working on these cars, it sounds very like one of 2 things. Either the throttle body is badly choked up with deposits or possibly the inlet manifold gaskets are leaking...which is not uncommon with these models.
Start by removing the throttle body assembly and thoroughly cleaning it with a plastic bristle brush and good aerosol 'carb cleaner'.
If you are anyway handy with a spanner, it's a relatively straightforward job.
Also make sure the spark plugs are in good condition as these are often ignored during service due to the awkwardness of removal.
Keep us posted if u get sorted.

The_Nipper_One

Thanks for the pointers Maztech. I would like to keep you posted, but unfortunately I'm not able to reproduce the condition at will, so I wouldn't know if your suggestions worked due to the usual gap of weeks/months between it happening. I guess you could assume that until you hear from me again that it is fixed