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Discussion Starter · #1 ·
I have two problems that I'm sure some have experienced in the past. One is the wiring to the CPS. Most of the time I can take my fingers and just lightly pinch (without moving the wire) the black wire on the wiring harness just before the CPS clip and the car dies immediately. Of course, moving the wires around will kill it also, but sometimes I can grab and move them and it never misses a beat.

The second problem is the Lexus AFM electronics. How does it react when it goes (or starts going) bad. I am getting a code 12 (CPS) as well as a 31 (AFM) but it is hard to distinguish which is causing it to run irratically. After driving a few minutes, I'll start off from a red light and it will kill for a split second and then surge forward. It will finally get to a point where it won't idle when stopped and I have to keep revving the engine to keep it from dying. I suspect that is the AFM electronics, since the CPS wiring problem usually means I have to get out and move the wires around.

I'm trying to get ready for the Supra meet in June!
 

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If you still have your stock AFM replace the Lexus electronics with the stock AFM ones and see if the problem goes away. If you have a code 31 you probably have an AFM or wiring problem. Frankly I'd buy a new 7M harness while you can. It'll save you a lot of trouble.
 

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Discussion Starter · #3 ·
I'd like to buy a new wiring harness but I can't talk myself into dishing out $400 to $600 for one.
 

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one of the best investments out there for the 7m guys hands down.
Seconded, Still available from Mark @ Toyota!!! Around 500 to 600 IIRC.


You need to investigate your wiring on your CPS & CPS plug. I recently rebuilt my CPS (new bearing and seal) and guess what? After 21 years the CPS insulation had become so brittle it pretty much flaked off with a fingernail after pushing on it. It was already cracked and had 0.5 to 1.5mm cracks in the insulation. This is both INSIDE and OUTSIDE the CPS.

Aaron @ Driftmtion.com sells new CPS pigtails as well. They're not too expensive either... something around $20 or less I think.
 

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Discussion Starter · #6 ·
If you still have your stock AFM replace the Lexus electronics with the stock AFM ones and see if the problem goes away.
I tried this and it ran the same. I think I must have a wiring problem. I noticed the wiring ties the cps to the afm together so I guess I will start tracing wires. If I can't find it I will consider a new wiring harness. It would be nice if I could find a new one for $600 or less. I would probably spend two or three hundred having someone find the problem.
 

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I'm not sure why you think it $600 but its probably less than $400 at least mine was. The problem is only 90+ harnesses were available so you'd have to swap to the newer ECU if you had an early car. I'd ask Mark what you can actually still get. Eventually you won't be able to buy one regardless probably very soon.
 

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87-88 Harnesses are not Available last time I checked and last price quote that I recieved from Mark on a 89 harness was around $570 if my memory serves me correctly.
 

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Discussion Starter · #10 ·
I'm going to replace my cps and ox sensor wiring connectors first to see it that helps although I'm not to optimistic.
 

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Discussion Starter · #11 ·
I fooled with the CPS wires and it seems to be doing a lot better now. I disconnected and reconnected the battery to reset the codes. Before starting, I checked the codes to make sure they were clear. Cranked the car for one minute and checked the codes again and got an AFM code ( but no CPS code). I tried another AFM and still had the same problem. I'm not much on electrical, but I guess I will do a continuity check and see what I can find. The only problem is that the AFM ties into so many things that it is hard to diagnose.
 

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Sounds like you haven't fixed the CPS wiring yet. The CPS is the single biggest weakness(and most important sensor) in the 7M's wiring, since the exhaust cooks it. I'd fix that first.
 

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You feel that even though the code says it's the AFM it is actually the CPS?
Nope. If you:
  • Have stalling issues
  • Have had problems with the CPS wiring in the past
  • Haven't addressed the CPS wiring yet
I'd bet the CPS is still an issue.

My wiring to the AFM was pretty brittle too, and needed to be repaired. I'd go with a new harness if you can afford it, or just patch and re-pin any hard spots or sections with broken insulation.
 

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Discussion Starter · #15 ·
I untaped all the wiring and looked for any problems last night but didn't really find anything. I tried some continuity checks that did not test correctly before untaping that worked after untaping. Reset the codes, cranked the car for a couple of minutes and checked the codes again and there were none. Drove it for a ways and it ran fine until boosting and it tried to die on me a few times on the way home. It did die at a stop light, but cranked again and didn't give me any more problems. I really want to find the problem if I can. I hate buying parts and it doesn't fix the problem.
 
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