Revs up and down and up and... 2.5 V6

Starman · 4th September 2007, 10:00

Sorry for yet another thread..

I'm still trying to get hold of the garage that repkaced my belts,plugs etc.
Whilst waiting I thoughjt I'd stick me nose under the bonnet again. My engine sits ticking over albeit a tad lumpy but should I bring the revs up a small amount (say up to 1000) they start to drop and rise in a cycle.. the faster the revs the faster the cycle and the less the drop and rise! (think I noticed this also when driving and suddenly getting more oomph!)
Does this sound indicative of anything to you who know?
I don't remember it ever doing it before the work was carried out.
I'll see if any one here has a stab before I try calling them again.

cheers again for reading and poss helping.

Simon · 4th September 2007, 20:35

Could be a timing issue? I can't really be any more specific as I'm not too clued-up on the more in-depth side of the engine timings and all the associated sensors and what-nots. Hopefully someone with more in depth knowledge will be along to advise with a little more detail....

Lates · 4th September 2007, 21:00

Bounce it straight back to be rechecked.Could be a multitude of things to be honest, belt timing, failed sensor,faulty plug causing misfire. Either way if it didnt do it before it needs mending now - and not at your expense.

KHC · 6th September 2007, 17:55

If not timing (a cam is misaligned off one belt notch) It sounds like the MAF - Mass Air sensor - could be playing up - Bosch OBD2 diagnosis of your engine management system data might be needed. Not a regular issue for 2.0 V6 though as I think the Diesel has issues in that area.

This surging problem is a recurring problem with other cars - my Boxster needed its MAF changing in April - and improved significantly but I think one or two coil packs are still playing up....

Have you had a performance air filter fitted? The oil on those can trash your MAF that leads to spurious data to the ECU - hence the surging and lumpy tickover.

It could be as simple as an air leak in the induction side somewhere.

Keith · 7th September 2007, 12:28

Steve if this is a DIY exercise first thing I would do is clean the IAT valve if sticky or jamming sligtly you will get an uneven tickover especially if as a result it is over compensating

Beyond that you are into all sorts of choices airleaks sensors, ignition etc
Is the performance ok as I would have thought a incorrectly fitted belt would cause far more obvious problems but Lates would be better able to advise re that

Starman · 7th September 2007, 13:53

Thanks everyone.

Car goes in on tuesday for investigative work.

yes Keith there is defo loss of power even with both vis motors dead...esp. bottom end!!

I have put a green cotton panel in but only 200 miles ago,thanks khc.

It was a lot better before they got their hands on it

Thanks again :lol:

4th September 2007, 10:00	#1
Starman Posted a thing or two 03 CDTi Tourer Conn SE auto Join Date: Jul 2007 Location: Shrewsbury Posts: 1,405 Thanks: 0 Thanked 15 Times in 4 Posts	Revs up and down and up and... 2.5 V6 Sorry for yet another thread.. I'm still trying to get hold of the garage that repkaced my belts,plugs etc. Whilst waiting I thoughjt I'd stick me nose under the bonnet again. My engine sits ticking over albeit a tad lumpy but should I bring the revs up a small amount (say up to 1000) they start to drop and rise in a cycle.. the faster the revs the faster the cycle and the less the drop and rise! (think I noticed this also when driving and suddenly getting more oomph!) Does this sound indicative of anything to you who know? I don't remember it ever doing it before the work was carried out. I'll see if any one here has a stab before I try calling them again. cheers again for reading and poss helping. __________________ [SIGPIC][/SIGPIC]

7th September 2007, 13:53	#6
Starman Posted a thing or two 03 CDTi Tourer Conn SE auto Join Date: Jul 2007 Location: Shrewsbury Posts: 1,405 Thanks: 0 Thanked 15 Times in 4 Posts	Thanks everyone. Car goes in on tuesday for investigative work. yes Keith there is defo loss of power even with both vis motors dead...esp. bottom end!! I have put a green cotton panel in but only 200 miles ago,thanks khc. It was a lot better before they got their hands on it Thanks again :lol: __________________ [SIGPIC][/SIGPIC]

4th September 2007, 20:35	#2
Simon Banned - Join Date: Nov 2006 Location: - Posts: 10,318 Thanks: 0 Thanked 4 Times in 3 Posts	Could be a timing issue? I can't really be any more specific as I'm not too clued-up on the more in-depth side of the engine timings and all the associated sensors and what-nots. Hopefully someone with more in depth knowledge will be along to advise with a little more detail....

4th September 2007, 21:00	#3
Lates This is my second home Jaguar XE Join Date: Nov 2006 Location: Coventry Posts: 4,321 Thanks: 56 Thanked 59 Times in 55 Posts	Bounce it straight back to be rechecked.Could be a multitude of things to be honest, belt timing, failed sensor,faulty plug causing misfire. Either way if it didnt do it before it needs mending now - and not at your expense.

6th September 2007, 17:55	#4
KHC Newbie R75 Connie and 986 Boxster Join Date: Jul 2007 Location: Hereford Posts: 27 Thanks: 0 Thanked 0 Times in 0 Posts	If not timing (a cam is misaligned off one belt notch) It sounds like the MAF - Mass Air sensor - could be playing up - Bosch OBD2 diagnosis of your engine management system data might be needed. Not a regular issue for 2.0 V6 though as I think the Diesel has issues in that area. This surging problem is a recurring problem with other cars - my Boxster needed its MAF changing in April - and improved significantly but I think one or two coil packs are still playing up.... Have you had a performance air filter fitted? The oil on those can trash your MAF that leads to spurious data to the ECU - hence the surging and lumpy tickover. It could be as simple as an air leak in the induction side somewhere.

7th September 2007, 12:28	#5
Keith This is my second home ZT400 Join Date: Oct 2006 Location: Ellesmere Posts: 5,948 Thanks: 0 Thanked 43 Times in 29 Posts	Steve if this is a DIY exercise first thing I would do is clean the IAT valve if sticky or jamming sligtly you will get an uneven tickover especially if as a result it is over compensating Beyond that you are into all sorts of choices airleaks sensors, ignition etc Is the performance ok as I would have thought a incorrectly fitted belt would cause far more obvious problems but Lates would be better able to advise re that