Hi guys/gals.
Got a v5 type R and noticed the last couple of timesI have drove her that when at lights the revs fluctuate up and down to nearly stalling and the boost gauge goes with it.
It is not happening all the time it happened once today in an hours drive and once last sunday again once in a 2 hour drive...
Anyone came across this before. was thinking maybe air/vaccuum leak but surely it would be every time ???????

 

Could be the onset of airflow sensor failure - when was the last time yours had a new one? Do you have a knock monitor on, and if so is it showing more noise under boost?

What do you mean by the boost gauge "going with it"? Theoretically it'll be at -0.6 to -0.7 bar or so of vacuum at idle. Are you saying that the vacuum begins to subside - and then re-establishes as the engine picks up again?

 

do you mean MAF ? not sure I have had the car 5 months and I have not changed it. it had a full API rebuild 2 years ago not sure if they would of changed it its not on the paperwork. so I am unsure..

Also yeah you are right with the vacuum ! I think that might be normal though as the revs are changing !

 

Yes.

Sensors made in the last three years or so have a date code printed in white ink on the mounting flange, along with a stripe of green paint, so firstly have a look and see if you can see one or both of those things - it'll confirm if nothing else whether you have a recent-ish one.

Beyond that, if you have a method of monitoring knock or directly monitoring the sensor output, you'll probably already know if it's degraded. Try resetting the ECU first - but be prepared for that not to solve the problem.

If all else fails, the other way of testing would be to fit a brand new sensor, reset your ECU (again) and see if the problem is fixed. If it is, then you know what it was. If the near stalling is still there, you know it's not the MAF, can put the old one back in, and put the new one back in its box and leave it on your shelf for the next time you think you might need one (which you unquestionably will).

Incidentally, before too long, someone will probably pop on telling you that you can test for a knackered sensor by unplugging yours with the engine running and seeing if the engine stalls. If so, be aware that this test does not work and can both damage good sensors and give misleading results. You're better off not trying it.

 

Ok so if it is one that is marked up as mentioned is that good. ? was there problems with the older types ?
thanks for your help by the way and yes i have heard of that test but never liked the sound of it

 

Ahem, how to put this. The new ones are better than the older types, but even the new ones aren't perfect. If it's marked up like I said then it means you don't have a really old one, but even the new ones go - they just fail less often than the older sort!