rough idle please help

[shannonspeelman1231]

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]

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]

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]

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]

I look for one for you ok!

[shannonspeelman1231]

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]

Here you go:

[shannonspeelman1231]

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]

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

[BoostedFC]

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

[sidewaysFC]

my car has idle problems when its cold I have to hold the gas untile it worms up a little bit I was thinking it was ether my wax pellit ,fast idle cam or my bac valve , and I read in the haynes manulle to check the bac valve you unplug it wile the cars runing to see if the idle changes I unpluged it and the idle didnt change so would that be my bac valve

[shannonspeelman1231]

k check your bac with an ohm meter it should read between 10 an 20 ohms if it does its good try that an let me know is your car a turbo

[sidewaysFC]

its an na and im going to check it as soon as I get some batterys for my tester

[shannonspeelman1231]

ok so im gonna have to get a new tps and a new bac this high idle is pissing me off ohh an i caught my exhaust on fire today cuz the guy who had the car before me a blow the old motor up didnt clean the exhaust an there is a bunch sitting in it still so pist ohh an i ran out of gas while i was driving it so does anyone have a tps or a bac i can buy that works

[sidewaysFC]

what happend to your exhaust

[BoostedFC]

I don't have either, I'm sorry man. Have you checked your local parts yards?

[sidewaysFC]

ok im not to good with an electrical tester but I got 14 ohms , so its gotta be my fast idle cam or thermo wax pellet how would I adjust that or fix it.

[BoostedFC]

Disassemble throttle body. Some have completely done away with them both.

[sidewaysFC]

what you mean the wax pellet and fast idle cam go bad a lot.

[shannonspeelman1231]

they guy blow the old motor up in my car. when that happened the oil was forced into the turbo an thru the exhaust where it collected yesterday i fixed my idle problem almost i guess its still around 1000 rpms but i took it for a ride and it was smoking real bad so i turned back an headed home. when i got home i popped the hood an checked everything was good all my fluids everything was right so i let it idle with it still smoking when my budddy said het oil is dripping out the exhaust so i looked it was funny but i wasnt loosing any oil pressure or oil so i reved it up a lil an some more oil shoot out so i shut the car down an u could hear the oil bubblin in the muffler it was too funny spent most of the day cleanning it out no the car doesnt smoke at all thats what happened to my exhuast i still need a tps sensor but the car is running strong

on a second note can anyone tell me how to adjust the boost for more psi this 10psi shit sucks is there a way like on a sti to adjust the waste gate or the diverter valve

[shannonspeelman1231]

another ? how hard is a front mount an how does it work cuz i was looking an there is alot of vac lines an the diverter tube i guess im probably just over thinking it an would a front mount be better for my car

[BoostedFC]

You can adjust the boost with a boost controller (manual or electronic). Are you asking about a front mount intercooler? Yes a FMIC is a good upgrade, the stock top mount is limited to it's size as well as heat soak from the engine bay. FMIC's can be easy to install assuming that you don't buy a cooler that takes up half of the front bumper.

[BoostedFC]

If you are ever around my way, I would like to see the car.

[shannonspeelman1231]

i will b in va around may 22nd im gonna bring the car if its running good we can meet up then i can try an put a pic up too it needs paint its black an white at the moment an yea i think im gonna do the front mount cuz all this taking an puttin on the top mount is getting old lol an the fmic wont b huge either i dont wanna cut the bumper im trying to make it look just like the intial d fc3

[BoostedFC]

Oh I thought you were in VA._

[shannonspeelman1231]

no im in ohio right now spending time with my dad since i just retired out of the military

[BoostedFC]

Okay I got you, well if you come down in May let me know man.

[sidewaysFC]

I want to see it to put up some pics

[shannonspeelman1231]

go to my ablum an u can it wont let me post them here

[shannonspeelman1231]

u gonna have one of your runnin when i come down in may i wanna find a fb an fd next really want a twin turbo fd just dont wanna pay alot for it

[shannonspeelman1231]

here r the pics i figured out how do do the pics lol let me know what u think i know i needs work not sure what color wanna kinda stay with the white but i love orange an blue just dont know gonna sand it down when the rain stops an prime it :D:D:D

[BoostedFC]

Not sure I'm unemployed right now I have plenty of time, but no extra money to put towards the car.

BTW the car looks fine a little time & money & you will have her right.

[shannonspeelman1231]

yea i have the time too but no money also lol u think i should keep her white

[BoostedFC]

As it being a 10th anniversary I would keep it white, but that's me. BTW I have a friend that I think has a set of the fender emblems for a 10th anniversary he was going to sell me. I could see if he still has them if you want them.

[shannonspeelman1231]

yea cuz i want another set so let me know