My car has an intermittent engine problem. I am not going to say what I think it is as I want an un influenced set of suggestions.

 

There is nothing obviously wrong, it runs absolutely brilliantly, strong as an ox. Smooth brilliant... then with no pattern or trigger that I can find it runs really badly.

 

It has done it most at 60/70 in fifth at a neutral throttle, it suddenly has a subtle "open closed open" throttle sort of faulter. In a lower gear it is a non rhythymic but obvious drop of power as if its running out of fuel.

 

It can also come with backfiring, if I slow to a stop when it is faultering it backfires on overrun then in neutral the revs bounce from 250rpm to 700rpm in a "brup-brup-brup-brup" sort of a way then it will stall.

 

It does it for a period of time then is fine again.

 

The problem is there for about 10 minutes every hour I drive it.

 

Really stumped, hope we come to some good ideas guys :)

Just need to monitor AFR when the issue is occurring as there weren't any DTCs recorded. I would have said possible CAS issue, given the backfiring.

or a MAF issue if it's backfiring

So next time it plays up, pull over and while it's faultering and dying, unplug the MAF? Or the CAS? See what it does.

 

Coukd these things be that intermittent?

It'll stop running if you unplug the cas, but give it a wiggle to see if it smooths out.

 

Is it only part throttle when playing up, ie does it sort itself out with full throttle?

So next time it plays up, pull over and while it's faultering and dying, unplug the MAF? Or the CAS? See what it does.

 

Coukd these things be that intermittent?

 

It's another odd one, was absolutely perfect for the couple of hours I spent with the car. Had forgotten just how well it drives, one of my favourites. Great lambda feedback as well, which is a real rarity :wack:

 

Sensors can go awry without throwing a code. You can unplug the MAF and it will have a 2500rpm limit. If the symptoms cease, that's the culprit. You will end up with a code afterwards though.

 

Try to refrain from "driving through" the issue, in case the fuelling or timing is a long way off. You don't want to place the engine under load at this point.

Has the ECU been chipped ?

 

once the problem starts and you do a full ignition/engine off, wait 10 seconds and turn ignition/engine back on, does the issue disappear (for a while) ?

It'll stop running if you unplug the cas, but give it a wiggle to see if it smooths out.

 

Is it only part throttle when playing up, ie does it sort itself out with full throttle?

 

At full throttle it has a soft hesitation as it carries itself over the problem. I have only tried a copcouple of times. Normally as I carefully accelerate at 1/4 throttle it cuts hard, but that could be me flinching off the throttle as it cuts.

 

Perhaps some multi meter tests on these components?

I had a similar problem that was the cas. Tell tale signs where the Rev counter flicking about and backfiring.

I had a similar problem that was the cas. Tell tale signs where the Rev counter flicking about and backfiring.

 

Did that produce error code 11 in your case?

No I didn't get an error code as far as I can remember. I believe I had to try another cas to see if it was that. Which it was in my case.

 

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I am hesitant to go replacing electrical units, could rapidly get pricey, so I hope I catch one red handed and can do just that, I have 2 MAFs as well to make diagnosis a bit trickier.

I think getting a 2nd hand CAS to try would be the first step to take as far as replacing components is concerned. As discussed, it is important to monitor all signals when the issue is happening. AFR too to further diagnose if it's more of a mechanical issue, even if it's ultimately caused by an erroneous electrical signal.

 

For the meantime, try & replicate the issue, jump out the car and start frantically wiggling electrical terminals :wack: