Bad idle

[works]

Hi lads car starts fine after a second it wont idle u have to keep it revved up done a compression test getting 70psi on the 2 rotars and no vacum leaks im loosing patience wit it as i cant drive it any help did a search on it but have checked a few other things also like tps settings

[the hat]

what kind of compression tester are you using

[batman]

map sensor ?

[Brett]

Is it a Turbo 2 or a non-turbo?

[Adam fc]

Brett,what did u say was the cause of the random irrattic idle on the black t2?? was it a vac leak?? sorry just couldn\'t remember what u said it was:(

[works]

used a halfords one wit the valve held in and its a turbo 2 think the map sensor is ok when i unplug it she cuts out

[Brett]

IIRC ot should be part of the cold start system... for some reason my mind has gone blank on the names of the parts  Doh!

[Prof]

70 psi is under 5 BAR - which is very low - but what RPM was the engine turning over for that test ?
 
The engine could be losing compression and that\'s why it won\'t idle well.
 
If you keep your foot on it for a little while will it run ok once warm, or can you not get that far with it ?

[works]

yea if you hold your foot on it a bit she will stay running will drive to but wont idle at lights its like its ported the way it idles if thats any help..i was told by a rotary specialist the 70 is spot on and that mazda lowered it to 60 is this correct

[the hat]

my car does idle low on cold start its like its not seeing the car is cold and as it gets warmer it idles perfect any one know what controls the cold start system

[Brett]

If its a Turbo then start by checking the BAC valve on top of the inlet manifold - if that\'s failed it won\'t idle IIRC.  Reove it and put 12V accross it - the valve should open and shut as power is added and removed.

[works]

is this bac thing over the turbo kinda and does it have black pipes going onto it

[Prof]

That\'s the one - the 2 black pipes on the outside edge ot it are water pipes - just to help warm it up.  The larger black pipe that goes underneath feeds air into the engine bypassing the throttle plates.  The BAC valve is fed with a pulsing duty cycle to control the opening of the valve and hence how much air is allowed into the engine once the engine is warm.  It compensates for electrical loads and power steering loads.

[TiddlesRX7]

Yep thats the one. A pipe going in from each side and an electrical plug on the right.




Edit
Beaten to it by Prof as usual!

[mukumu kurubushi]

i was told by a rotary specialist the 70 is spot on and that mazda lowered it to 60 is this correct

I think thats minimum compression pressure set by Mazda, 60 is for the FD. Good compression is 100psi + so, like Prof said if you are seeing 70 on your comp test, thats quite low. I used the same Halfords tester as you when i checked mine.

I\'m also trying to get to the bottom of a low idle (with a stumble coming off throttle) which got worse after installing an underdrive alt pulley. Apparently adjusting the TPS can solve a lot of idle problems so that\'s where im gonna start, then looking at the BAC next.