Help! Supra doesn't run right

Abe's 1987

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#1
Here is my situation. My 1987 turbo idles erratically between 1000 to 2000 rpm. When i try to rev up its like it hits fuel cut at 3000 rpm and won't rev past 3000 rpm. So far I've tested tps, iacv, vacuum system, timing, and afm. All seems to be within specs. Ive checked to make sure my spark plug wires were on right and torqued the plugs to spec. Compression of all cylinders were within 118 to 122 psi dry test. Oil pressure is within specs. I changed fuel filter. I checked for boost leaks and fixed a few leaks. If I pinch the hose going from the iacv to the intake the idle stops fluctuating but still won't rev past 3000 rpm. I had to fix a couple vacuum mishaps. I even turned the throttle idle screw clockwise and counterclockwise but didn't help. But still having the problem. Tsrm doesn't seem to have any troubleshooting for my situation. Any pointers, tips, or similar problem repairs would be great help. Ive been using the tsrm and just can't pin point my problem.
 
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plaaya69

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#3
Are your grounds good coming from the engine wiring harness going under the intake manifold and also the main grounds that go on the block and cylinder head?
 

Abe's 1987

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#8
Ok checked grounds all good. Had to order a cold start ignition timing switch as mine was broken. Installed it and it didn't make a difference. Only last thing i can think of is ecu. If anyone has one at a good price let me know. It is a 89+ turbo 5 speed manual, I'm guessing the year as the engine had been changed. I will get the part number by tomorrow night off the ecu.
 
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Abe's 1987

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#9
So far tsrm has been a great guide compared to most repair manuals I've used in the past. To bad it can't diagnose my car for me. Lol. I'm pretty sure that is called a mechanic. But yeah still looking for a ecu. I'm pretty sure that is my problem. Or even I could borrow one just to see if that's the problem from anyone I'd appreciate it.
 

Abe's 1987

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#11
I check the afm as the tsrm says to with a multi meter and I got the ohms reading within specs. I also opened the ecu and everything looks to be good. When i get the supra started no check engine light. I jumped E1 with TE1 and the check engine light just blinks continuously none stop so i guessed that means no codes. At this point im stumped. I've have come to a point where I guess I just have to keep swapping parts out to find the issue. Problem is that is going to cost a pretty pennie.
 

Abe's 1987

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#12
Only thing I haven't tested was fuel pressure but I don't think it would cause these issues would it? But yeah if anyone has some extra parts I could use to eliminate possible suspects aka (tps, iacv, afm, ecu, ect.....) to loan I'd be willing to pay shipping and ship it back as soon as I test it I'd appreciate it.
 

plaaya69

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#13
When my AFM got destroyed along time ago (Because I used crc mass air flow sensor cleaner when it first came out and it had no warnings on the label like it does now "not to use in Toyota Supra Turbo") it would not go past 3k rpms. Usually also when the ISCV goes bad it will make the Supra idle at 3k rpms. I made a quick video of my turbo Supra running with the AFM unplugged and the symptoms it shows. Is this how yours is running?

https://youtu.be/MQHoO1Pz3MI
 

Abe's 1987

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The things I do notice now since fixing a few of the problems the idle does now fluctuates between 1500 and 2000 rpms and now it wont rev past 2500 rpms. The starter was tested good as its a new starter but as you can hear in the videos it has problems starting, not sure why it does that.
 
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3p141592654

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#16
Has it ever run properly with the setup you have there? One thing I notice is the lack of a fan shroud right next to the AFM with an exposed filter which could be causing turbulence at the AFM. Try shielding the air filter from the fan with a piece of cardboard or sheet metal. Also make sure the honeycomb is still on the front of the AFM.
 
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Abe's 1987

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#18
So it has been running like this since i bought the supra. Ive had it for coming up to two months. I will check all these in the morning.
 

Abe's 1987

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#19
Ok so the honeycomb is on. I also decided to double check the ohms reading of the tps, iacv, and afm. So now the afm has no readings even though prior it was reading within specs. And I think based on my readings I has to also adjust the tps or it is bad as well . Iacv is still reading good.
 

3p141592654

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#21
Before you do that place a shield between the fan and the afm. These afms are sensitive to turbulence and that setup you have is pretty near worst case. Also. For now you can unplug the tps. It will run ok without it and remove one more uncertainty for now.
 
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Abe's 1987

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#22
Trying to see if I can find an afm and tps for a good price. But the question I have is i already have the part number for the afm but I don't have for the tps. I'm getting conflicting numbers for the tps. I need the part number for the pre 89. I figured based on my ecu that my swap is a 86-88.
 

Abe's 1987

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#23
Before you do that place a shield between the fan and the afm. These afms are sensitive to turbulence and that setup you have is pretty near worst case. Also. For now you can unplug the tps. It will run ok without it and remove one more uncertainty for now.
Im going to do this tomorrow and see what happens.
 

Abe's 1987

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#24
Ok so I bought a new tps and used afm on eBay just waiting for them to come in. I also bought some sheet metal to build a casing around the filter. Had to fix the steering column as the locking mechanism was jammed and the steering wheel was going all over the place. Found a few cut wires on the column which I'm fixing. It is most likely the horn and cruise wiring as they don't work. Will keep you guys updated.
 

Abe's 1987

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#25
Got the new tps in today. Spent about one hour adjusting it to specs. Waiting for the used but known working afm and will install both in and also make the cover for the air filter to compensate for the lack of a fan shield. Once all is done hopefully (fingers crossed) it should run right. I have fixed all the cut wiring i found under the steering column and behind the horn. It was all for the horn and cruise control. The curise control was also broken at the mounting spot so i superglue it back together and reinstalled it all back together. Seems to be a good fix. Still tones of work to come. Will most likely have to adjust the timing once I get the idle set right.
 

Abe's 1987

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#26
Ok got the tps and afm sheild installed today. Fluctuating idle has stopped but still hits fuel cut when revved up and idles at about 1500 rpms. In my mind when I first got the supra i accidentally touched the positive terminal to the alternator ground. Could that have messed up the ecu? Cause it seems like the fuel cut is getting worse meaning it's hitting fuel cut at roughly 1500 to 2000 rpm instead of 3000 rpm.
 

suprarx7nut

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#34
I believe that square wave looking thing at 5 o'clock on your voltmeter is the frequency setting.

On one hand, seeing an engine bay that rough makes me cringe... on the other I'm jealous because you can make it so much better with just a bunch of factory used parts. I get some weird satisfaction bringing things back to life.

Keep us updated here. That sheet metal shield looks far better than I expected.
 

Abe's 1987

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#36
I believe that square wave looking thing at 5 o'clock on your voltmeter is the frequency setting.

On one hand, seeing an engine bay that rough makes me cringe... on the other I'm jealous because you can make it so much better with just a bunch of factory used parts. I get some weird satisfaction bringing things back to life.

Keep us updated here. That sheet metal shield looks far better than I expected.
Yeah I'm working on getting the thing running then will make it look pretty.

And the sheet metal shield is just temporary so I didn't expect it to turn out this good
 

3p141592654

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#38
From an internet search that square wave setting on the multimeter is a 50 Hz square wave generator, so that won't help.

My guess is the AFM is bad and once you replace it with a good one it will run fine, so hopefully the one you ordered will solve it. Still, That whole air filter contraption makes me nervous so close to the AFM.