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Discussion Starter · #1 ·
Hey guys i got a 1983 supra and the motor is running like it has a giant vacume leek, but i've searched for hours and found no problem with any vacum system. I've looked at th mass air flow sensor and throttle body, and the both opening and closing smoothly. I've had a few mechanics look at it they think it could even be a head gasket but my water and oil are fine. I also replaced the cap and rotor and plugs. I'm only seventeen and don't have a lot of oney floating around to have a mechanic start fidling around. i have also done the heater core and radiator and thurmostat. So any ideas would be helpful thanks
 

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Did you get the car this way or has this just happened?

My suggestions in order of probability.

Vacuum leak you haven't found. Try spraying some starter fluid in suspected locations. Do a search and you can find a vacuum diagram that will show you where to look.

Leaks in the intake tubing/couplers. Sucking air after the AFM will cause this affect. The spray test would find that as well.

Anybody messed with the timing? If you got the car this way, get a timing light and check the timing. You'll need to jumper a test lead to accuratly set the timing. A search will yield the procedure.

You've already stated you did a tuneup. I notice you didn't mention plug wires. Were those replaced? If not, you may have a cylinder not firing or firing poorly. Did you notice anything unusual about the condition of the old plugs when you replaced them? You can do a quick test for a bad wire by pulling them off one at a time while the car is running. It it doesn't affect the way the car is running, you've found the culprit.

Test the AFM. Test procedure can be found in the TSRM which is available on line. A faulty AFM could be sending bogus signals to the ECU.

Compression test. If you don't have access to a tester, find a cheap tool wholesaler like Harbour Freight and you can pick up a compression tester for a reasonable price. TSRM contains the acceptable ranges, but typically, they should all be fairly close to each other. If you have one (or more) way low, it's probably a head gasket. I had one blow between the cylinders, so no water in the oil and it had this effect.

Could also be fuel related, i.e. fuel filter, not expensive but a bitch to change. Possibly a weak fuel pump. You would need to test your fuel pressure, also available for cheap at Harbour Freight. Fuel pump is external on your 83, so is fairly easy to change.

EGR can cause similar issues in certain instances. ISCV (Idle speed control valve) could also be a culprit, but typically it primarily effects idle. There are other possibilities, but try these first and see what you come up with.
 

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Bad air filter?
Clogged cat?
Any codes?
 

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blown headgasket maybe but does it run like shit all the time or when it heats up and mechanic worth his nut should be able to find it within an hour of looking find better mechanics
 

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broken woudruff key on the crank can cause similary problems. check your timing marks (on the crank and 2 cams) Vacumm in the intake is constantly changing at idle, that make it run very rough and loss of power too.
 

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Discussion Starter · #6 ·
I did everything i could, the timing was the same, compression was good despite the 300000 km on it. So i told the mechanic everything that i had done on it, i told him to go throught the fuel system first, hope hope a mechanic can find the problem for me. Thanks for the help though guys.
 

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Hey bud

You should check your Idle control valve. It's located at the front end of the intake manifold, and has two connections to the wiring harness. It's a little bit of a pain to get off, due to the location of the two bolts holding it in place and the lack of space provided to get a wrench in. I was having similar issues with my 5mge, idle dropped to 400 rpm when sitting at a red light, ran fine while I was driving though. Check that part it could have quite of bit of gunk on it. Just use some carb cleaner on it and that should do the trick. If that does not help, the part could be going out. But, I would check other avenues before jumping to that conclusion. Only because that part is ridiculously exspensive new, 300 from autozone and 600 from toyota. But, Im sure you could pick one up off a parted out car at a junk yard or from a forum member perhaps. Anyways, I know this is lengthy, just wanted to throw it out there.
 
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