Be very very careful. The 4 screws holding the iac on will strip very easily. Make sure you have the right screwdriver and that it's not worn down. Honestly that's the hard part of the job.

Also they sell iac cleaner. It's safer to use than carb cleaner. Consider buying a can of it.

 

The IAC doesn't have much to do with hesitation on acceleration, usually a dirty IAC manifests itself as a rough idle, especially in gear when stopped with an auto trans, though even with a manual sometimes you can get a pretty rough idle to the point it feels like the engine might stumble and die.

It'd still be a good idea to clean the IAC, it's sometimes fairly easy to remove the four screws holding it to the throttle body if you get a really good Philips #2 screwdriver. You can use IAC or throttle body/air intake cleaner, it should all be safe to use since it's formulated to not remove protective coatings. You may need to use a squirt of carb cleaner if it's really stuck, though. I used a lot of IAC/TB cleaner to get the buildup out but it took a shot of carb cleaner to unstick the valve itself. Just wash it out immediately with the IAC/TB cleaner. I also used a cotton swab/q-tip and a spiral motion to get into the corners and crevices - that helped a lot to absorb some of the crud that wasn't washing out on it's own.

You may also want to get a new IAC gasket, they are rather inexpensive and most auto parts stores can get them under the Mahle/Victor Reinz brand.


While you're doing all that I'd highly suggest cleaning out the MAF sensor, throttle body, and checking/replacing the air filter, PCV valve, and even the intake tube from the inlet to the air filter box for obstructions. You may also want to pull the spark plugs and check to be sure they are NGK/Denso plugs and in good shape, and inspect the wires for any wear or damage.

 

Yep, IAC only manages... idle, and only when cold. Once engine's warmed up, IAC should be fully closed and contributes nothing to idle air.

Most likely you've got intake-leak between MAF and intake-valves. When opening up throttle, this leak sucks in extra air that's not metered by MAF and results in lean mixtures. Takes a fraction of second for this extra air and lean mixture to hit O2-sensor in exhaust and ECU compensates with fuel-trim.

 

Man, you guys are awesome and thanks on educating me on how iac works i have also noticed when i floor the car, the check engine light blinks (cylinder misfire) i have to check the intake valves for leak that will be hard thing to do unless you guys give me some ideas.

p.s i have also replaced plugs with denso 3324 while i removed the plugs i noticed the plugs were covered in oil, thats the top part that face the coilpack

 

Get the code from a scanner as to the misfire blink engine light. Should tell you which cylinder misfired. Swap the bad coil over pack with a good one and see if the code moves. If yes buy a nice new denso coil pack replace and enjoy.

 

Intake-valves won't cause any problems, because they can only suck in air that's going into the head. It's intake-tracts leading up to them that's issue. Hose-clamps, cracks in hoses, leaking intake-manifold gaskets, cracked vacuum lines, even injector seals can cause leaks, etc.

BTW, what brand MAF do you have?

 

MAF is OEM i have never changed have only cleaned it and hesitation slightly was reduced i bet i will have to dedicate myself on 4th of july figuring out intake tracts

 

Read my post 17 of 17.

https://www.toyotanation.com/forum/...la-8th-generation-1998-2002/1485498-just-took-possession-1999-corolla-ce-2.html

 

If you end up taking off the throttle body to get to the iac valve and unstick it, check the vacuum hoses right downstream of it before reassembling. You will probably need a new throttle body gasket and definitely a new iac valve one. I had one of the vacuum hoses on mine cracked and causing random misfire, but it was on the underside of the hose and hidden away so I didn't notice the crack until after I had replaced the TB, intake, exhaust manifold, IAC valve and donut gaskets along with injector o rings. MY mpg went way up because of all of it but I could have saved some money if I had found the leak first.

You've been given good advise though if the misfire is located at one cylinder; just swap the coil packs and replace the one that's bad, which is easy enough. If the plugs are covered in oil you may need new tube seals/valve cover gasket. The valve cover gasket is an easy job on this car and shouldn't take more than an hour if that even the first time you do it. Obviously replace the spark plugs as well if they are coated in oil.