Car cuts out/won't idle

tberry6686

Looking for any suggestions.

Got car back the other day after about 4 months in the garage (don't ask). Car went in for an MOT and needed some work doing to it to pass Brake disks, pads, corroded brake line etc nothing drastic or to do with the engine.

Car is pretty much undriveable at the minute as it does not idle - just cuts out as soon as the revs drop, when I do drive it it is a bit like a kangaroo at 2500rpm as if the engine power is just coming as a pulse instead of being continuos.

It drove perfectly when it went to the garage originally.

DUTR

tberry6686 wrote: »

Looking for any suggestions.

Got car back the other day after about 4 months in the garage (don't ask). Car went in for an MOT and needed some work doing to it to pass Brake disks, pads, corroded brake line etc nothing drastic or to do with the engine.

Car is pretty much undriveable at the minute as it does not idle - just cuts out as soon as the revs drop, when I do drive it it is a bit like a kangaroo at 2500rpm as if the engine power is just coming as a pulse instead of being continuos.

It drove perfectly when it went to the garage originally.

Sadly the reason it has been standing for months does come into it, the type of car would help too, perhaps after a few miles of driving the car will right itself.

Richard53

If it's got carbs, then I would put money on it being gummed up jets from the fuel sitting in there for 4 months. Not the end of the world.

If it's fuel injection, you'd need to start looking elsewhere, but the 4 months idle is a key fact.

And yes, details of the car would help.

tberry6686

Ive put about 20 miles on it since I got it back, not easy with junctions etc as it won't keep going unless I can keep the revs up, (and no handy local stretch of motorway either)

It's a mazda MX5 mk 2. It was only standing in the garage till the Work for the mot was done with no work to the engine or electrical system that I am aware of.

TrickyWicky

I don't know the model but off the top of my head it sounds like a sticky ICV (Idle Control Valve) or a TDC / cam sensor.

Worst case scenario (it is a mazda afterall) is the headgasket but if it's been sat for 4 months doing nothing this shouldn't be an issue.

ICVs can become a bit sticky though and these are what they're called - valves that open and close / adjust themselves to keep the air flow at the correct rate for idling. If they're sticking then the engine will become irregular as it idles. On that line of thought it's also possible that there is a MAF sensor that isn't happy but I wouldn't have thought this would be the case.

You could also have defective coil packs if it has these OR defective coils. I wouldn't have thought this is the case but it is possible.

DUTR

tberry6686 wrote: »

Ive put about 20 miles on it since I got it back, not easy with junctions etc as it won't keep going unless I can keep the revs up, (and no handy local stretch of motorway either)

It's a mazda MX5 mk 2. It was only standing in the garage till the Work for the mot was done with no work to the engine or electrical system that I am aware of.

Still not sure why you don't beleive a car standing for months without usage won't have some initial teething problems that may clear after some regular usage, perhaps a service is required? Plugs checked, air filter.....

Richard53

TrickyWicky wrote: »

I don't know the model but off the top of my head it sounds like a sticky ICV (Idle Control Valve) or a TDC / cam sensor.

I had very similar symptoms with a 3.5 V8 in an old Range Rover. This turned out to be exactly this issue. On the RR, it was easy to dismantle and clean the valve (which cured it, for the time being) but not sure if the MX5 is as user-friendly.

Richard53

DUTR wrote: »

teething problems that may clear after some regular usage

Or an Italian tune-up

tberry6686

I'll pull the plugs and air filter tomorrow to check them (if it stops raining here). The 2 runs I have done with it have been with the revs kept high (2.5 - 3.5k) just to allow me to change gear without it cutting out on me so I don't think an Italian tune up will really help (nowhere local to try it anyway). I'll see if I can locate my OBD reader and see if there are any fault codes stored as well.

Car_Complaints

Just to clarify, when you say "stood" did the car actual stand still for 4mths or did the garage owner move the car in and out on a daily basis to make more space for repairing other cars?

TrickyWicky

DUTR wrote: »

Still not sure why you don't beleive a car standing for months without usage won't have some initial teething problems that may clear after some regular usage, perhaps a service is required? Plugs checked, air filter.....

Well it shouldn't really. The only things that can really affect it are things that might have sticky oil etc on them and then they get sticky and don't move properly etc. We have a car that sat there dead for over a year. When we finally got it going it moved around quite happily with no major issues.

Coils, head gaskets, sensors etc shouldn't fail and as the car IS moving but having trouble at idle it sounds more like a sticking ICV or even throttle body.

It could possibly be a temp sensor as that would be causing the ECU to adjust the fuel flow at idle.

Those are the ones I'd check first, ICV, thorttle body, temp sensor.

Duff coils / coil packs would make it hard to start and you'd hear some cylinders not firing properly (engine would sound rough as hell). Duff TDC / crank / cam sensor probably wouldn't even let the car start as the ECU wouldn't know what position the engines internals are at.

MAF sensor.. I doubt the sensor is at fault but check the air pipes and air filter to make sure there are no air leaks. Any air leaks (where air can get in after the sensor) will mean the sensor doesn't detect enough airflow and the ECU will then try to adjust the engine badly - dropping the idle and then picking it up in a regular hunting pattern. I had this happen once, !!!!!! to find but once I realised a clip was missing and put it back the car idled perfectly.

So to recap:
Check ICV (if you have one), perhaps lube it with some WD40 or brake cleaner. Not entirely sure how you'd test it but I suppose you could squeeze the pipes to restrict the airflow and then see if it tries to adjust but someone else may have a better method.

Air leaks around the air inlet, filter, throttle body and ICV

Throttle body - check for sticking.

As the op hasn't mentioned if this is when the engine is hot / cold / both the temp sensor would be my next guess after the previous three.