HELP! INTERMITTENT IDLING PROBLEMS

BOF · Post by **BOF** » February 12th, 2007, 6:10 pm

HI there guys! Forum newbie here, but I know a bit about cars. The car is a 97 MX-3 V6 manual, and the problem is that intermittently it idles roughly, or even stalls, on a closed throttle. It runs perfectly under load at all times, though, i.e. when the throttle isn't closed. It's my wife's car, so I need to fix it to get some peace....

I've only got the Chilton manual, which is not hugely detailed or model-specific. If I had this problem on my own car (SAAB 9000), I would be looking to clean out the idle air control valve by flushing it with carburettor cleaner. Would this be a good start for the MX-3? If not, where should I look first? I'm sure I'm not the first to have this problem. Please help - I'm being nagged to death here!

BOF

mab · Post by **mab** » February 12th, 2007, 6:55 pm

start the car get your throttlebody cleaner out and at idel spray around the upper intake manifold listen for any idel changes around where you are spraying. also spray around the backside of your throttle linkage. intake cleaner burns and if you have small vaccum leak thats the way to find out. it sounds like a vaccum leak. 90% of the time thats where you get idel problems on these car. good luck

kiwi_MX3 · Post by **kiwi_MX3** » February 12th, 2007, 6:57 pm

This is why im single and the R1 is not setup for a passanger....

Umm interesting problem, what rpm is the car idling at? possibly
it is set to low?

ryan_Fuerte · Post by **ryan_Fuerte** » February 12th, 2007, 9:12 pm

deffinetly agree with mab, sounds like a vacuumm leak.

BOF · Post by **BOF** » February 13th, 2007, 5:30 am

Thank you gentlemen. Just what I hoped for - I knew others would have had the problem. I'll try the carb cleaner spraying route before I get the tools out, though as the fault's intermittent, it may be tricky to find it.

Kiwi, it idles at around 700 rpm when it's OK, which is most of the time. Running the aircon raises the idle to 1000 rpm or so. I understand that two terminals in the diagnostic socket have to be bridged - a paperclip is ideal, I gather - to set the idling speed manually; can you confirm which two?

When it's recently started, and therefore running on rich mixture, the problem does not occur.

I'll let you know how I get on. Thanks again.

Den

BOF · Post by **BOF** » February 16th, 2007, 9:09 am

Thank you, gentlemen. It was indeed a vacuum leak - cracking between two ribs of the large rubber induction manifold between the air cleaner and the throttle body. I'm now £60 poorer, but the Dragon is happy......

Thank you again.

BOF

PWRD_BY_HKS · Post by **PWRD_BY_HKS** » February 16th, 2007, 11:39 am

yeah ...watch out for those hoses....they tend to for the wierdest reasons just totally unplug them selfs....

Tempus · Post by **Tempus** » February 16th, 2007, 12:35 pm

Cracking in that ribbed intake pipe (between MAF and throttlebody) can cause all sorts of weird problems depending on where the crack is.

Because that part flexes as the motor twists slightly in its mounts, the flexing can have the effect of opening and closing the leaks.. When the crack opens and air flows in (bypassing the airflow sensor) the MAF reports less airflow to the engine so the computer gives it less fuel, the mix goes lean, power drops.

but WHEN the crack(s) open or close can depend on where the crack is located, top, bottom, side, etc. for some folks the leak closes when the engine is unloaded and at idle, so it's fine at idle but stalls when they try to accelerate. For other folks it's the reverse, it's fine when there is load that torques the engine slightly in it's mounts (like going down the road, fighting wind resistance or accelerating) but opens up at idle speeds causing the car to stall unless you keep your foot on the gas..

Same root cause, very different symptoms