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shannonspeelman1231 04-16-2011 12:11 AM

rough idle please help
 
ok first off hi to everyone im a bran new owner of a 1988 mazda rx7 10th ann. here is the problem it was just rebuilt when i got it it wasnt running wasnt getting fuel. i have it running now but the idle is rough it idles low then high like 500- 1900 rpms it seems like a vacuam leak to me but im not sure the vacuam is all over the place it dies right around 10 on the boost gauge please some one help

BoostedFC 04-16-2011 12:44 AM

I pulled this from a member on another forum for you to look at.

the fc idle system at first glace seems complex and pointless but is actually very simple.

the parts:

throttle body, the throttle valves that are controlled by your foot.

double throttle system, on the na its simply hooked up to a thermoswitch that closes them when the thermowax is not up to temp.
the turbo does this too, but they additionanlly use the double throttle as some sort of damper.

thermowax: wax pellet in coolant, it literally bumps the throttle open cold and gradually lowers rpms as it gets warm

bac valve: meters air around the throttle body to raise engine speed

accelerated warmup system: like the bac, but its bigger, revs engine to 3000ish rpms on a cold start

air supply valve: same as bac, but this one kicks up the idle 100-200rpms when the ac is on, or you move the wheel in a ps car

tps: tells the ecu the throttle position

ecu: from the rpm, and tps, and afm it needs to calculate the bac duty, and the aws/air supply conditions, so it can deliver a good idle

afm: meters all of the total air in the system



how it works:

when you start the car cold, the ecu will open the aws and dump in a bunch of fuel. the car starts and revs up to 3000rpms for 30seconds, unless the throttle is blipped or the car is put into gear. the idle will come down to 1500-2000 rpms because the thermowax is pushing the throttle open slightly, and the double throttle should be closed. as the car warms up the thermowax also warms up, and starts lowering the idle until it eventually pops off (it is adjustable both for how long it stays on, and how high the rpms are). the double throttle opens here too. once the idle drops to spec (750 +/-50) the bac valve will take over, its job is to keep a steady 750rpm idle. they do this by duty cycling a solenoid (like a fuel injector) so it passes the correct amount of air. if you turn on the ac, the idle will kick up to 1000-1100 rpms due to the air supply valve turning on. its job is to keep the engine running under large loads like ac, or using the power steering at idle.


problems:


throttlebody: occasionally they will stick, this will keep the idle too high. also on the na's if you adjust the throttle stop for the secondaries and they hang open it will cause a large 1000-2000rpm surging

double throttle: on the na's failure leaves it open, its also possible to have a vacuum leak at the double throttle diaphram

thermowax: since this is in coolant its got a couple ways to be wrong.
if there's an air bubble or a blocked passage it can be stuck on, and idle high. it can also stick partway on intermittantly, and result in an intermittant high idle. or it can be bad and not come on at all. it is adjustable so if it sticks on this is usually fixable

bac valve: i have yet to see a dirty one on an fc, but theoretically they can get dirty and stick and you will get either a high or a low idle.
also on the turbo the hose from the bac to the intercooler pipe can split and cause a low idle due to the vacuum leak. the last failure mode is just plain failure, this will give you a low idle (500-600)

aws: the valve can fail stick shut, nobody will miss this if it doesn't work.

air supply valve: this is the same as the bac valve, only it wont give you a low idle, it will idle low/stall with the ac on, or when you move the steering wheel on a ps car

tps: causes all sorts of weirdness, its very important to the output of the ecu

afm: if there are vacuum leaks it will cause a low idle. the afm meters all of the air, if there's more coming in from a vacuum leak, it will be lean and idle low if at all

adjustments:

s4 na: on the top of the throttle body there is an idle speed screw. and by the airbox there is the idle mixture screw. the only important thing about the idle mixture screw is that if its fully rich or lean and you have a working air pump/acv then there is something else wrong (vacuum leaks)

s4 t2: the idle speed screw is on the bac valve on the right side of the intake above the turbo. idle mixture is like the na

s5's: same as the s4 except they don't have the idle mixture adjustment

As with any diagnostic routine, don't rule out other causes of rough idle, such as:

Low/ uneven compression
Fouled spark plugs/ arcing plug wires
Incorrect spark timing
Fuel pressure/ volume/ pump voltage/ regulator internal leaks
Poor grounds/ harness plugs
Loose intake boots/ clamps
Vacuum leaks

shannonspeelman1231 04-16-2011 07:21 PM

ok i have tried all that still nothing anyone know where i can get a tps sensor the bac sensor does anyone know where i can get a vacuam diagram

shannonspeelman1231 04-16-2011 08:36 PM

ok so here is some more info please help i think it is my tps because it idles around 2000 then it just drops off and stalls i could b wrong but can someone hook me up with a vacuam dia gram please

BoostedFC 04-16-2011 08:59 PM

I look for one for you ok!

shannonspeelman1231 04-16-2011 09:11 PM

i really love this car i bought 2 just so i could get my 10th ann running i had cancer an this was my dream car so i got it as a present for winning my battle its hard for me to work on im still kinda weak i really wanna drive this thing so bad i could use all the help i can get so thank u to anyone who helps me

BoostedFC 04-16-2011 11:03 PM

2 Attachment(s)
Here you go:

shannonspeelman1231 04-16-2011 11:04 PM

ok so i got it too idle now i changed the tps an it idles but its real high 2000 how long does it take to warm up its still smoking out the tail pipe but it is running strong took it for a ride man does it move i hit 13 psi at 3000 rpms so i think i still have a vac leak

shannonspeelman1231 04-16-2011 11:06 PM

thanks for the diagram man i really do appreciate it its gonna b alot of help
:D:D:D:D:D:D:D

BoostedFC 04-16-2011 11:11 PM

If I can find any other diagrams I'll post them.


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