4ac Wont Idle Below 1100, Stalls Under Heavy Braking

[Le|Garage]

hey guys, got abit of an engine problem here. The car is a 1983 AE71 automatic. New spark plugs, ignition coil, leads, brake master cylinder, front brake pads

 

When i start the car in the cold, i have to hold the throttle down and keep the revs at around 1200 for around 30 secconds before i let it go, or it will stall..

 

After that, It will drive perfectly, revs out cleanly. (it idle's at 1100 rpm). It wont want to idle any lower, when i adjust the idle screw, or it will splutter and stall. Standard factory setting is 800 rpm isnt it?

 

Okay, now under heavy braking the car will stall. If i brake gradually, it is okay, but if i brake hard (like..normal braking), the revs will fall to around 600, and then it will try and catch itself and stall.

 

I've been told it could be a "brake booster" problem? What could be the fix for these problems? Cheers!

[Trev]

Sounds alot more like a vacuum leak, Check out the vacuum hoses, When you have the car stationary in park/neutral and pump the brakes does it idle up?

[Le|Garage]

Sounds alot more like a vacuum leak, Check out the vacuum hoses, When you have the car stationary in park/neutral and pump the brakes does it idle up?

 

I've tried checking all the hoses i know of, but i'm unsure which ones i need to check? I have got the air duct hose, the oil breather hose, a vacuum hose and some other thin hose going to the air filter box ontop of the carby. I've checked them and they all seem okay, is there any other one i should be checking? Does anyone have a vacuum line diagram?

 

When i have the car stationary, and pump the brakes, idle doesnt change

[kryton brown]

It's also possible that the idle passages and/or idle jets in the carby are blocked.

[Le|Garage]

okay, well i set the timing with a timing light. And now it will idle at 800 rpm. It will sometimes jump from 8-850, but it idle's okay. Checked all the hoses going to the carburetor and their all fine. There are no hoses plugged to the heater core. COuld this be affecting anything?

 

Still though, it will stall if i don't brake gradually, the revs will drop, real low and the car will stall when i brake. Any ideas? Could it be the brake booster? Is there any way i can check it? Cheers

[DearmanKE]

mine seams to drop in revs when applying the brakes but not so much as stalling, i would like to know why this happens to.

[Budowski]

Mine doesnt sem to drop much when i brake, but i can't get the idle mixture right or the fast idle. Isuspect i have semi blocked passages in the idle circuits but once off idle runs great.

Ive checked every vac line all ok, havent checked the booster yet tho but i doupt its that.

[w13c]

i think the culprit is the 4ac's electronic/auto choke,

mine is similar in that it idles at 1100, and revs drop heaps when you first accelerate.

i took my filter off, and when i start up the auto choke doesnt budge, its just all floppy.. trying to figure a fix atm.

[AE80Rollaguy]

YEAH !!! i have pretty much the same problem but in reverse! today all of a sudden my 3ac idle's at around 500rpm and seams to be really fuely..

 

On the topic of webbers.. Has any one fitted a 32/36 webber to there 4ac? where could i get an adaptor plate from?? much help needed

 

cheers Tory

[w13c]

haha yeah i was thinking the exact same , going the weber, i noticed this adaptor plate on ebay, if it helps

 

http://cgi.ebay.com.au/WEBER-ADAPTOR-PLATE...Q2em118Q2el1247

[Budowski]

going webber is very easy as seen on club 4ac

[orangeLJ]

how big of a bowl do the carbies have?

 

Under heavy braking you could be experiencing some fuel slosh in the bowls, causing a loss of fuel, and the drop in idle.

 

similar (but different) thing used to happen to an old torana I had, under full brakes or heavy accelerationthe float would move around in the bowl on the carb, causing it to flood.

 

Is the carby in good condition?

Edited October 8, 2008 by orangeLJ

[Budowski]

picked up 2nd hand carby a while back and forgot about it, its dirty as hell and when i dropped it in the car runs perfect after i adjusted the mixture and fast idle crazy eh :P, had a carby on a 97 hiace sent out for rebuild at work cost 185 dollars.

[Nitephyre]

I'm having these problems as well, but mine is manual.

 

Brakes are spongy and the idle is shit... I so want a Weber again, they're great.

[mog_uk]

having the same problem, mine just started this morning, could it be anything to do with air in the brake lines/ effecting the brake master?

 

I'm going to check

-

 

braking when stationary - see if idle increases

check vaccum lines for brakes etc.

 

 

afew people mentioned things to do with the carby. how and what do i need to check for?

 

its a manual 4ac.

 

-thanks