hey guys my 94 celica st when hot or cold will fluctuate its idle. it will bounce up and down about 200 rpm and when listening to the exhaust it sounds like it misses every once in a while. i bought new spark plugs, spark plug wires, front o2 sensor, fuel filter, and i took out the throttle body and cleaned it all up. well mainly the butterfly i didn't try taking off the IACV and cleaning it. As a side note i do not have any check engine lights on, and yes it does work.

Any ideas on what it could be?

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Had same issue on my after doing some work on the car.Try to reset ECU, cure the problem but after some time came back.Gave up at the end

Mine is doing the same (5sfe) replaced the IAC motor and plugs/wires/cap/rotor and never fixed it.

I am the farthest thing to a reliable source for this advice, however, let me at least try to give you some ideas.

It sounds like the computer is having trouble knowing how much fuel to add to maintain idle. Flashing the ecu might work, but it could be that some type of sensor is too dirty, malfunctioning, has come loose after 20 years of life or needs replacement. O2 sensor only inspects the exhaust manifold to see if the mixture of fuel and air is running richly or leanly, so probably not the sensor your looking for.

Perhaps the fuel filter is dirty and struggling to give gas efficiently?

I don't think any compression issues are present, but it can't escape my mind, maybe check?

https://www.youtube.com/watch?v=8oJyRHaqksM

This is a kind of terrible, kind of funny but actually very similar video to your problem, perhaps check it out.

/edit: sorry, I forgot to mention that the video actually is about a honda, but the concepts are the same. He checked the car for leaks in the air intake system, contacted the dealership and produced nothing. He eventually found it to be a cooling issue. Replacement of the coolant and rad cap, burping the system and problem was solved. Not something I would of thought about, but check it out.

This post has been edited by HaysoosKreesto: Oct 31, 2014 - 1:58 AM

take the IACV apart and clean it if you haven't. test the Coolant Temperature Sensor with an ohmmeter, look up the specs in the manual in the stickies. make sure your accelerator cable is mounted properly on clips and not laying on the exhaust manifold. You may need a timing light to set the ignition timing. and how old are the plugs, wires?

This post has been edited by VavAlephVav: Oct 31, 2014 - 6:24 AM

Mine feels more like a occasional hard miss. I've done everything that VavAlephVav has suggested except test the coolant temp sensor. I'll test it and see if its bad.

the other thing which I haven't tried yet, is get a usb to OBD2 cord on ebay, get OBD1 to OBD2 adapter if yours is <96. you can find the Toyota TIS software on bittorent, then use your laptop to get a good look at the system.
but my friend has one that works from a Bluetooth OBD2 plug to an App on his phone, idk which will work better or if it will do you much good with OBD1

And, have you replaced the ignition coil inside the distributor? maybe the insulation is breaking down and it leaks spark when you hit it hard.

This post has been edited by VavAlephVav: Oct 31, 2014 - 4:20 PM

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IACV is good spot to start. If you are sitting at idle and push the gas just a tiny bit (raise maybe 100rpm) does the fluctuating stop?

Does it stop bouncing once it's fully warmed? Does it bounce worse once fully warmed?