Need Help Fast!! What would cause this?

[Festiva_Fred]

Okay, my 93' Festiva w/ATX started idling at 1500 no matter what today, and it also fluxuates between 1500 and 1700ish rpm while idling. It goes up down up down.. etc.. not matter what. The car drove alright on the highway today, just seemed to be getting not-as-good gas mileage. It just started acting up today, the other day it was fine and idling at 750-800 rpm.

If anyone could help out that would be great.
-Fred

[slacka_6]

might have a vacuum leak... cracked hose or intake tube...

[doylerl]

On a newer car, with everything being ran off the computer, I would point to idle air control valve, throttle position sensor, or map sensor. I know the festys have a TPS, but I am not sure about the rest. also, as slacka said, it may just be a vacuum leak.

[FestYboy]

sudden vac leak...

[miami man]

lean surge

[FestYboy]

^really!? a steady 1500 rpm idle from lean surge? think about that a sec and you'll see why i'm questioning that statement.

[wybnrml]

^really!? a steady 1500 rpm idle from lean surge? think about that a sec and you'll see why i'm questioning that statement.

But he says it goes from 1500 to 1700 up and down, so it could possibly be a lean surge right.

[Festiva_Fred]

Update! Swapped out the intake assembly from one of my other festivas onto the car and that brought the idle down to around 1100 and it's steady now. Must still have a leak somewhere else..

[JohnGunn]

So your idle is now steady at 1100. Would you say that is about the same speed as your previous fast idle at engine start up? Or when the engine is started cold now what is the speed?

There are two sources for a suddenly increased but stable idle speed. ISC stuck open so that fast idle speed does not shut down as the engine warms up. Or vacuum leak into the plenum.

To test the former. Disconnect the two large hoses from the ISC, one at the plenum, the other at the air intake duct. Cap those connections with rubber caps that can be bought at AutoZone, or whatever, in an assorted size collection for about $5. Then start the car. There will be no fast idle and you may have to keep it running by use of the accelerator. When it is warm read the idle speed. If it is back to the speed you had before the problem surfaced, then the ISC is defective. It should start open on a cold engine and gradually close as it warms.

If bypassing the ISC in this fashion does not bring you back to the set idle speed. Look at all the vacuum hoses that attach to the plenum. Follow each of them using choke cleaner spray at connections to see if that causes the engine to speed up. Also use the choke cleaner to test the throttle body to plenum gasket.

To make it short, report back the following:
1) idle speed at cold engine start up.
2) idle speed after normal engine temperature is reached.
3) idle speed with ISC bypassed and engine at normal running temperature.

That will give us enough to narrow the search significantly.

John Gunn
Coronado, CA

[gestiva]

my car has same symptoms...
same 1300 idle speed, from start up till warm. no change.
only happend since i took engine out and re installed it,
themostat locked and started to over heat, so i took it out,
now idle is consistant 1600?

WILL CHECK THOSE TOMORROW.
i at first thought it was from thermostat, will install new one too, to make sure

[JohnGunn]

See what effect bypassing the Idle Speed Controller has. (Described in my previous post in this thread.) Also, when it is bypassed and the engine is warmed up and running, blow through the disconnected air intake duct hose. It should be completely closed. Report back how open it appears when you blow through it.

Here are three links to the cap assortment I suggest you buy.

http://www.dormanproducts.com/p-9-02253.aspx

http://www.autozone.com/autozone/catalog/accessories/accProductDetails.jsp?counter=1&categoryDisplayName=Automotive+Help+and+Miscellaneous+Products&fromString=search&itemIdentifier=426020_0_0_&productId=426020&sortType=&parentId=1314-10&filterByKeyWord=bypass+cap&categoryNValue=101314&navValue=101890&fromWhere=&itemId=1890-10&displayName=Cooling+Bypass+Cap&store=2808&skuDisplayName=2+pcs.+each+3/8%2C+1/2%2C+5/8+and+3/4+in.+cooling+bypass+cap+assortment&brandName=Help

http://www.oreillyauto.com/site/c/detail/DOR3/02253.oap?partType=N0262&parentPartType=C0142

Of course, you only need two caps from this assortment to bypass the Idle Speed Controller. As I recall they are different sizes, the one to the plastic air intake duct is 3/4" I.D.; the one to the plenum is 5/8" I.D.

John Gunn
Coronado, CA