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Discussion Starter · #1 · (Edited)
I've got a 7MGTE that was running mostly fine (fresh rebuild, unknown history) and it was running fine for about a week now then one morning it wouldn't run correctly - here's the video. At the end, you can see how rough the idle is through the shifter bouncing.
Video - 7MGTE

Under light load it's a bit worse. Feels about like running very low on fuel. It will rev throughout the range and feels better under heavier load.

I've checked
Timing, spark, fuel pressure, wiring, grounds, igniter, coils, CPS, solenoid resistor, TPS adjustment and all is in spec, I've also checked the wiring to CPS and coil harness.

The AFM shows rising frequency when accelerating and decreasing frequency while decelerating, but it does not fall in spec according to the 1987 TSRM (wildly out of spec actually) - however, I noticed that they removed most of the resistances and checks in the later TSRM so I'm unsure if this is the culprit or even a symptom of what is happening here. It also seems to have an occasional but subtle pop out of the exhaust and is slightly more pronounced when revving it. It feels like when the timing isn't correct, but its ignition timing is 10 btdc and with the diagnostic port not jumpered, its between 12 and 13 verified by timing light. Cam and crank timing seems to be dead on, however "TDC" as measured by piston movement is actually dead center between 5 and 0 on the crank pulley. Even still, I'm not sure that 2.5 degrees out would cause this kind of drivability issue especially after it's been running fine.

I'll post more details as I think of them or find them - this has been a mystery for 3 days now.

Any suggestions at all would be greatly appreciated. Thanks in advance
 

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1987 MA71 R154 Pearl White, Blue Velour
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I could be wildly off but it "sounds" like the exhaust might be plugged, vacuum line or VSV is not working, MAS unit is shot, or something along that line. I know that's vague. Did it happen all of a sudden?
 

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Discussion Starter · #3 ·
It was driving fine, I parked it and the next morning - this. I know the exhaust isn't plugged as I just pieced it all together and installed it last week.

When you say MAS, are you talking about the air flow meter? That is an item in question and theres not a significant change with it plugged in vs disconnected, however it does show a frequency response correlating with airflow on a meter.

Also regarding the vacuum, I do also question the EGR and related vacuum components, but am unsure if the 7M responds this poorly to a stuck EGR or VSV failure.
 

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1987 MA71 R154 Pearl White, Blue Velour
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Yeah the Mass Airflow Sensor that lives on the intake pipe as it leaves the air filter. Mine was not working correctly and I managed to source one from the junkyard.

I'm going through VSV replacements now. Turns out my EGR VSV (green line) was bypassed years ago by a mechanic when they did my head gasket (1997) lol. I had long forgotten that but I managed to find a new one that I get on Tuesday. (actually was available new in Dubai. I wonder how long its been sitting over there.)

The other VSV (blue line) is the one that is related to fuel pressure. That one a hose tee had broken off so not only was it not able to function correctly, but a major vacuum leak.

Map World Organism Line Font

Here's a link to that thread I put up 87 7M-GTE VSV question
 

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89 Turbo - 2JZGE-T VVti (build/swap in progress)
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Sounds like it's misfiring to me. First I'd do a compression test just to make sure. Then, try idling it with the AFM disconnected. If compression is good and it still does it with no AFM signal, check the coolant temp sensor (the one that goes to the ECU).
 

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Discussion Starter · #6 ·
Thanks for the reply. I’ll get the compression test done in the next couple of days.

In the meantime, I did disconnect the afm and there is no significant difference running with vs without except without throws a code.
 

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Discussion Starter · #7 ·
Thanks for the coolant temp sensor idea. I definitely overlooked that. The shop is 68 degrees currently and according to the tsrm, it should measure 20k ohms, but I’m getting a reading of less than 100 ohms. Even if it’s not the issue, it looks like that needs to be addressed so thanks again.
 

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Thanks for the reply. I’ll get the compression test done in the next couple of days.

In the meantime, I did disconnect the afm and there is no significant difference running with vs without except without throws a code.
I'll be very interested in the results of the compression test. From your video, my 7M sounded exactly like that and turned out to have low compression on cylinder 6. Hoping you've just got a bad sensor or something.
 

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1987 MA71 R154 Pearl White, Blue Velour
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Yeah I'm starting to understand the importance of each sensor recently, and how they all work together.
 

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I once knicked the coolant temp sensor wiring on my 7M. I think the ECU freaks out and starts dumping fuel if it doesn't know how hot the coolant is.
 

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Discussion Starter · #11 ·
Two more questions -

One - Is there any way to tell if the OEM injectors are in place? It's an 87 - I noticed that a lot of 87s had yellow injectors. Mine are black - Were there variances in color? It's extremely rich and I'm wondering if this is part of the problem - although after reading above, that could be the coolant temp sensor.

Two - My fuel pressure reading is bouncing about 7psi when opening the throttle body. I've swapped FPRs, one does read a little lower so I'll switch back to that one, but this bounce seems extreme and I would assume this is an injector issue but I'd like to know if this is a somewhat common failure mode on another part in this vehicle so I can look there as well.
Fuel pressure video - YouTube
 

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1987 MA71 R154 Pearl White, Blue Velour
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Check the VSV for fuel pressure up above in blue. Make sure all vacuum lines are intact.

The VSV is not where it shows in the diagram. Its up under the intake manifold, right between the alternator and front knock sensor. You can see it if you shine a flashlight through the alternator area space from the front of the engine.

In my case, the air filter and one tee were broken clean off.
 

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Discussion Starter · #13 ·
Compression test results are in…
1) 143
2) 140
3) 148
4) 143
5) 145
6) 145

Engine was cold, results are without adding anh oil. Unfortunately I let it warm up and found that my compression tester had been damaged so in the time I cleaned up and purchased a new tester, the engine had cooled completely. Oh well, I think the numbers are in spec especially considering it doesn’t have enough drive time for the new rings to be seated yet.
 

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Glad to see you've got no dead cylinders. How about that coolant temp sensor? You could try disconnecting the plug and seeing if the car runs better, worse, or the same
 

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Discussion Starter · #15 ·
I am waiting on a new coolant temp sensor but haven't run the car since updating this thread.

Just as an update for others who may have a similar issue, I ended up pulling all the injectors to do a home cleaning / flow test and while pulsing the injectors, I found that one would pulse irregularly and also stick open between those irregular pulses. I'm guessing it has a big chunk of debris in it. I will do a thorough ultrasonic cleaning and report back but I think I may have found the culprit. 🤞
 
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