After 6 months of ownership ive finally got round to looking into the flat spot problem with black beauty , my p2 mi16 ... it has a massive flat spot from about 4000 rpm all the way up until 5200 rpm , when it flies .... we tested the solonoid and the vacuum thingies , both working fine , so we tested the ECU , which came up with a fault on the knock sensor , so ive got one on order . hopefully that will do the trick ...If not does anyone know of any other common problems with these acav systems we could possibly look at ??

I wont have my Goodwood ready for this years sprint season , so i am thinking of having a go in my 405 mi16 p2 ( if we can fix the flat spot )...i will probably enter the Curborough championship ....It may not be as silly as it sounds ( its either that or nothing ) as the car is not much bigger or heavier than a 306 , and People have always praise the handling of the mi16 , so i will find out if it can walk the walk

right , i changed the knock sensor today , but still no joy , and its still coming up with a knock sensor fault ...so i have just purchased a replacement ecu for £15 delivered , lets see if that sees any improvement

i had the exact same fdault with mine, made it so depressing to drive, i changed coils checked the avac and piping etc. in the end i got a gti6 inlet as theres not 'change over' time with them.

People say that there no good as it needs mapping to suit but persoanlly i think they only need mapping to get the FULL gain.

ive just got , for £20 , a replacement inlet manifold , so will see if that helps , although ive not yet changed the the Ecu ...all good fun im actually taking it off the road in 2 weeks or so , in preperation for the lpg conversion , and will use my more fuel efficient ax gti for work..so will have plenty of time to tinker ..

Changed the Ecu today , with no effect ..so ive decided that im not gonna chase the flat spot anymore as i wont be going over 4000 rpm anyway because the car is going to be a motorway cruiser now anyway , due to the high mileage it will get ...4000 rpm equates to about 80 mph , so with wanting a clean licence , that is fast enough for me

i must say i did love it on the motorway, plenty of torque and a pleasure to drive...

There's a 2.0 mi in our club which has a flatspot like yours, they've tried almost everything without a result.

One of my le mans has a flat spot between 3-4000 rpm. She has just had a full service and I have tried some different (known to be good) coils, but its still there.

Like the OP it is no big issue for me at the moment as this le mans will only be used for another 15-20 days or so this summer and the majority will be motorway miles, apart for the trip to & back from the motorway that will hopefully be done at over 4000rpm. The problem will either sort itself out or something else more major will no doubt pack up and demand attention.

when was the cambelt changed last?

Its been known for the timing to be a fair way out due to the twin tensioner setup, belt tensioning is quite critical.

Not a problem experienced on the later XU7J4 and the 10J4R and RS heads as they use a single tensioner and vernier pulleys.

that was one of my thoughts on my flat spot ..maybe the belt is a tooth out ..another avenue to look down ..

didnt help the one in our club.

A long time ago, 2003 acording to the service history that came with the car, its done about 20k since the belt was last changed. The car has not been used much since early 2005, i bought her in September 2006.

Cam belt is next on the list to replace now she is up and running again, once I have the pennies spare.

Right , im back on the case after driving the ax gti to work for 2 months ive realised how much i miss the mi ..
ive sort of been barking up the wrong tree ...Ive joined a 306 forum ( s16) where this problem is more widely discussed/understood...so i update my progress as i go ( hopefully i now know what the problem is ) ..

that would be greatly appreciated

It seems that one of the most common problems with the Acav system is leaks from the pipes and the plastic joining T peices ....I didnt notice originally , that when i rev the car manually from under the bonnet , that there is an air leak at low revs ..so this will be my first port of call ....It is behind the Cylinder head ( a common area apparently ) where a pipe runs ....So i am buying a set of replacement pipes off a guy from the 306 forum ( in blue ) ...when fitted i will update progress ..

Righty ho ...an update ...Ive changed the inlet manifold for a Gti6 one , straight forward swap, seems ok initially but not really tried it too much due to it being sorned ..i have an mot due in 2 weeks so that will be my first real run in it ....there seems to be a little hesitation at about 3000 rpm, nothing on the scale of the acav flat spot though... but after that it revs freely .... But , with being into sprinting , i am thinking of getting rid of my sprinters ( ax gti , 309 goodwood ) as i am sick of maintanance on 3 cars , not to mention the laguna we have ..so im thinking of trying my hand with that ...so i will need the acav system back as i run in standard production ..will have to wait and see

Looking forward to the real road test, did changing the pipes help?

and where are the pics

well, i;ve just fitted a gti6 manifold to an RFY Lump I've fitted into a 205, and TBH it feels exactly the same as the engine in my 405 does, i.e it FEELS flat under 4k, but is actually accelerating with great vigour, till you hit 4k odd and it howls to the redline like they usually do.


the sound is part gti6 intake bark, but still Mi16 as its still using the Mi16 head and exhaust.

Hopefully the owner will be able to attend a PSOOC RR meet in a month or so and we can see exactly how healthy the unknown engine is, and how different the intake makes it behave.

Personally I'd love to try and fit the gtui6 throttle body to the ACAV manifold...

See, as we all know, the GTI6 doesn't have the variable inlet of the later Mi/S16, yet still makes stronger torque lower down than the 1.9 Mi16. Obviously this is partly due to 93 extra CCs but it must be the GTI6's different head spec that makes the real difference. Cams are milder aren't they?

yeah, PeterT said they are particularly mild, an inlet change makes more difference to the RFS engine than the RFY I think.

Just opening up this topic again ....The reason ?,well, ive been using the mi ( black beauty ) for work , and the t5 for carting the kids around etc etc . I started work on a new site ( i work as a joiner) and on the first day there i saw two guys stood by it , looking around it ...Later in the day the site foreman came over to me asking if it was mine ? was it fast ? etc etc ... If you look at my previous posts you will see that it happens quite a lot to me on sites , with young lads asking about it and admiring it ..but unfortunatly i have to tell them it doesnt go as well as it looks , so now im going to make it my priority to make it as fast as it looks by restoring the original ACAV system , as peugeot intended ( IMO it was the wrong decision to convert it to the gti6 inlet )...ive got all my original bits ..but i need a diagram of how to restore the system ...Any clues to where i can get one ??? GTi6 manifold for sale later in the year ..

Good luck,
If you ever find out why it has a flat spot, please let me know.

I don't have a diagram for you