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1986 Toyota Corolla GTS with a 4A-GEC has issue idling consistiantly

The car made famous by the Japanese animation, Initial D. It’s a beautiful car, and a lot of fun to boot, when it’s working right. The problem right now is that it has a slight idling issue, of about 500 rpms up and down, every few seconds. It’s getting annoying now; We’ve replaced all the vacuum hose, tripled checked it was in right, set the TPS, cleaned the TB, and replaced the (shot) gasket, checked the Aux Air Valve (or the Idle Air Control Valve, to you people at Auto Zone) And we’ve burped the coolant, twice. I’m about to go as bald as my dad from all the frustration this car has caused me, but since it’s way too much fun to own and drive, I’m not going to get rid of it any time soon(I’m seeing if it’s legal to get buried in it). So, anyone out there with any idea what might be wrong, please do tell.

You have done a lot but could you recap air, gas, oil change and filter intervals along with plugs and wires, maybe even distributor cap, rotor and coil, and any code checks, condition of the exhaust, catalytic converter etc. It may be one thing but throwing parts at it is probably more expensive than a proper diagnosis

Air filter is good, just replaced the oil last month, plugs and wires are some what new (~3000 miles on them) And we are saving up to replace the distributor, as we have confirmed it leaks oil, and we aren’t going to bother trying to rebuild it. We’ve checked everything there is to be checked (Have a repair manual from Toyota, thick as a phone book) No codes on it either. We use only premium, and the gas tank has been redone and the fuel pump has been replaced in the last few years.

i work with him on it it idles fine sometimes but others if you let it sit the idle goes up about 500 then drops down and does it repeatedly and sometimes it runs perfectly fine

I would go back and check everything on the Idle air control valve and temp sensor, wires,grounds everything.

Check the pcv valve just for kicks!

idle air control valve looks good its brand new and we just had it off when we cleaned the throttle body. it still looked shiny and everything but im not sure if the temp sensor has been looked at so ill tell him (the op) that we should look at it after school if we have time.

also the car chooses when it wants to do this sometimes itll run almost perfectly then others the rpm will just raise and drop raise and drop. lol gotta love old cars

Assuming that the idle is computer controlled … my guess would be a failing engine speed sensor (may be called a turbine speed sensor on automatics). Garbage into the ECU … garbage out.

Oops … I’m wrong, it’s not the turbine speed sensor. I’m thinking of the crankshaft speed sensor (if your engine has one).

I think the early AE86 models had the large intake manifold runners with the butterfly valves about midway that close for low RPM torque. There is potential for vacuum leaks at this gasket as well as the intake manifold gasket and around the shaft for the butterflies. You might try spraying some Wd40 or some type of carburetor cleaner around all these points to see if it affects the idle.

You could also be having an O2 sensor go out, if the rpm rises and falls on 8 second intervals, I’d look at that.

On the distributor, remove the cap and rotor, turn the engine until a vane is lined up with the line on the ignitor (Toyota’s term). Then slip a feeler gauge in the gap, a .010 should just fit. Then push on the shaft away from the ignitor to see if the gap grows. It is difficult to notice without the feeler gauge. If the gap grows more that .007 for a total of .017 or more when you push on it, then you need a new distributor. If it doesn’t and the mechanical and vacuum advances are working, then its probably OK, especially since your engine is running.

One last thing to check is the fuel pressure regulator.

The distributor is leaking oil. We are going to replace it anyways, as we believe that the oil is effecting the spark to #1. I will check what you suggested, though.

I have seen these “checked everything” situations turn into electronic control unit failures.

Old fuel injected VW’s would do this idle hunt when the F.I. harness had a bad ground (amoung a few other reasons).