Cold start problem - low idle.

[och]

Whats up guys, this problem just started yesterday. When I start the car, idle stays low, pretty much at 650rpm - which is the normal speed for when the engine is warm. It of course makes for a rather rough/vibrating idle until the car warms up. When it warms up, the car is perfectly normal, idle doesn't drop below 650, everything is nice and smooth.

So what could it be? I have a few theories.

1) ECT Sensor - it could be broken and telling the computer that the engine is warm, and therefor the computer isn't sending enough fuel. But I kind of rule that out, because that would create problems on acceleration while the engine hasn't reached operating temperature. Plus, on a cold start the exhaust has a heavy gas smell, so I'm more inclined to think that it isn't getting enough air.

2) Cold start injector - I really don't know how it works and whats its function. Can somebody shed some light onto that?

3) Idle Air Valve - thats my most likely suspicion. Could it be that its not opening and the engine isn't getting enough air? But in that case, wouldn't I still have a problem once the engine is warm?

 

[samsdad]

Firstly check for DTCs then check the ECT which is the most likely fault

 

[sideshow]

doubt dtcs will show to much

find the 12 or 14mm pipe that feeds the idle motor
start the car in morning when its cold and with a pair of long nose pliers
crimp this big pipe and see if it makes a difference
if it makes fk all difference then the idle motor is stuck shut
very common problem

the next problem is finding a good 2nd hand one
in usa might have some luck but here in aussie land they are getting rare as

 

[Cobber]

I put my money on the idle control valve jammed. Re build it if you can it its pretty easy to do.

 

[JuNiOr24]

could it be a dirty(or bad) mafs? In my 02 celica i had iacv problems and I was getting rpm jumpin up and down. I just broke down my TB( it was filthy) clean iacv and it went away.

 

[rma]

hey guys , am having the same problem here. the Iacv stays shut , I replaced it with a known good one and installed it open, on the first cold start it worked great , but after warm up it stayed closed and wont open again .

What causes this valve to open and close, where should I look now .
water temp sensor maybe..

 

[Zuffen]

The valve is driven by the ECU.

The ECU knows the idle speed from the TPS telling it the throttle is closed in conjunction with the ECO knowing the engines speed as it's controlling injectio and timing rate.

If the revs are low it will open the valve if high it will close it.

 

[Cobber]

When you shut the engine down you should here the valve cycle a couple of times?

If not you have a problem in the power relays to do with the ecu.

The ecu drives the valve fully open when the engine is switched off so it knows what position it is in and to allow for air to start.

Happy new year