Intake manifold leak?
Turbo Mini Forums

For as long as I remember my Mini has idled rough and been a bit doughy at low rpm (as well as drinking juice!). Even when I changed engines it was the same but the common part on the car was a Minispares intake manifold. I have always suspected an air leak but now that I have my MJ up and running the load gauge jumps around a bit at idle. Is this normal? It's a stock NA MG Metro except for MS manifold and LCB/RC40. I have tried tracing the leak MANY times and sealed everything as much as possible but no joy. I have a trace of engine load from the MJ uploaded. What do ya think?

evidently the map sensor can pick up a bit of variation sometimes, especially if your only sensing one half of a webber,

I dunno if what your seeing is too much variation, but a common fix is to stick somthing like a fuel filter in the MAP line to dampen the signal.

The common fix for a less than ideal vac signal to the MAP sensor is to fit a 0.8mm mig tip in the line along with the fuel filter to act as a damping resevoir This is normally needed with big duration cams but it may help and will be easy and inexpensive to try.
A good way to check for induction leaks is to play an UNLIT propane torch close to the suspected area of the leak, if your engine speeds up you have found the leak.
Regards
Dave

Edited by danboy on 21st Jul, 2007.

Ah, I like the propane torch idea, thanks guys. After fiddling about with a few different maps for the MJ I have smoothed out the idle a lot by using a lot of advance down low. I have heaps more torque now but I am just making up for the leak with the MJ. Just shows you how good this ignition setup is!

If you had a leak I don't think you'd read that much vac at idle....

alex

AlexF

True. I guess what started me down this route was I used a colourtune (not everyones favourite device I know) but it was flashing yellow and blue all over the place in time with the hunting idle. The manifold is the comon denominator in all my engines I've run so maybe I'll get the surfaces faced just for luck.

colourtune is next to useless!

alex

AlexF

The standard MG Metro engines are well known for a slightly lumpy idle, this is because (for a standard OE profile) the cam is quite radical.
I personally wouldn't worry about it.