As long as it's linear, with no drop outs its should be fine. Referring to '89 FSM, page F2-81 cites a resistance measurement spec for the TPS, full & narrow ranges. To test, disconnect the TPS connector, and measure resistance across the TPS connector terminals it references at closed & wide open throttle conditions. Do this with the engine at operating temp OR you can use a screwdriver to lift the fast idle mechanism off the thermo-wax plunger so the TB is not sitting at a high idle for the closed throttle measurements.

Full range TPS @ wide open throttle should be 3.4 - 5.1 K-ohms; at closed throttle it should be 600~900 ohms. The narrow range is 0.8~1.2K ohms closed, and 4.0~6.0K ohms WOT.

^ that is a good point, I've done both resistance and voltage tests on this TPS. I'm told that testing for voltage is more reliable because it tests the TPS under load. But I can cross-reference voltage test with resistance test and they should both be good. If one is good you'd assume the other is. If they aren't the same then something is amiss.

I've opened up my FSM to look over the checklist for rough idle. I'll go down the line and test all those.

One question related. The water thermosensor:
I'm curious if it would work to test the water thermosensor for resistance but at the ECU pin rather than the sensor itself?

Reason being, to test per FSM means removing it, draining coolant, etc. Is there any reason why I can't start with a cold engine to test resistance at the ECU and let the engine warm up while testing?

The problem with doing it that way is your DVM/ohmmeter puts some voltage across the terminals you're trying to measure a resistance across. If it's still connected to the ECU with power applied you could potentially harm the ECU. Also, unless you have a good aftermarket temp gauge, how will you know the water temp when you're taking the resistance measurement?

Assuming you do have a temp gauge, one option would be to run the car until warmed up, then jot down the water temp off the gauge and shut it down. Disconnect the battery. Then disconnect the ECU connectors, and do your resistance measurement across the two ECU harness connector pins that connect to the water temp sensor. That will only get you one test sample though, so you still won't know if the temp sensor works across its full range. IIRC, the FSM gives 3~4 temp points to measure resistance on that temp sensor.

Our RTek 2 shows the temperature reading from the ECU on the Palm. Does the 1.7 not have that capability?

If its a RTD or resistance temp device it should have table somewhere about the resistance readings. So say 1k ohm means 72 degrees. Wouldn't really matter if you got multiple readings as long as you get a good resistance reading.

Also resistance will determine your voltage. So if your TPS has a "dead spot" it won't matter if you're reading voltage or resistance. One you when off, the when on.

Yes I have an aftermarket temp gauge, a Prosport, which isn't name brand, but it' seems to be about dead on. The sender for the temp gauge is tapped into the front of the water pump housing and is taking a reading at the same spot the OEM thermosensor is.

I also have a temp gun I could point at the water pump housing, radiator, hose, etc.

I was thinking the same thing about taking multiple readings, per FSM. I could test as the engine is warming up. Turn off the engine at each temp test and continue to the next....ugh but that means taking the UIM off each time to get to the thermosensor harness.

No logging on Rtek till you get to 2

The FSM has 3 temps to take resistances at and what the corresponding resistance should be, but not really a full scale that I know of. I suppose I could take resistance readings when they are at the resistances for a specific temp (per FSM) check the temp of the coolant to see if they line up.

With the TPS, yes we are kinda saying the same thing...I was more round about. But laws of electricity say that if there is a dead spot in voltage test there will be one for resistance also. I meant something is amiss, as in it wasn't tested correctly..not probed correctly and such.

Don't need to take the UIM off... What I was suggesting in my previous post is you take your readings off of the 2 water temp sensor pins on the ECU connector, after disconnecting it from the ECU. BTW, the resistance reading you'll get this way will be a little higher than what the FSM states for the temp sensor, but it shouldn't be by much more than a few ohms. This is because you're also measuring harness cable losses to the sensor.

Forgive my ignorance, but I'm confused on how you're talking about testing resistance. IIRC the harness at the sensor is 2-pin. So to test resistance between those two pins wouldn't I need to find out which pin on the sensor harness corresponds to the ECU pin and then test resistance between that pin and the other pin on the sensor it'self?

I'm confused on what 2 pins on the ECU I'd be testing for resistance. 2E is the only water thermosensor pin on the harness/ECU. I originally was thinking I could put one DMM probe on that pin and one ground to chasis...but that's not the same as checking resistance at the sensor itself...or is it and I've simply overthought things and gotten myself confused.

For what it's worth, I was thinking the same thing about added resistance for the small load the harness will add.

My bad, I should have given you the reference to the schematic diagram on FSM page F2-8. If you follow the water thermo sensor wires back to the ECU connector on the diagram, you'll see you can measure your resistance between pins #2E and 3D. Pin 2E goes to the water thermo sensor and connects to nothing else; 3D is labeled "E2" on the ECU side, which I believe is a common +5VDC supply to a bunch of the sensors, including the water thermo.

I stepped away from the car out of frustration. Before I did that I tested the thermosensor at the ecu for both resistance and voltage. I couldn't test the lowest temp what with it being summer but the other temps checked out fine.

That same day I checked TPS and it's still good and at 1v. Took it for a drive and it seemed better idling but afr are still 10.8 at idle. Then between stops it developed worse idle and hot start issues. It did it 3 times and that's when I parked it for a week or so.

IIRC the IAT tested fine at the ECU. I'll look at my notes and also test it again, this time at the sensor.

I guess next up is to test AFM/MAF. One thing to note, I have a Cosmo AFM/MAF for a 13B. I'm assuming that could be a factor in the rich idle?

I have a spare set of coils to swap on in hopes of a magic bullet.

Is the ISC the same as the single green harness used to get CEL codes?

When checking timing I never jumpered anything. I simply got it warmed up, idling around 800ish and pionted a timing gun.

That could very well be the case, at idle and elsewhere in the power curve as the ECU uses the AFM as a primary input to manage FI. Is the Cosmo AFM a different part # than the original AFM that went with your ECU? I know AFMs are not interchangeable between S4 & S5 or T2 & NA's. I have no idea if the Cosmo AFM is interchangeable with anything else. What's the reason for using the Cosmo AFM, larger diameter opening/better flow?

I think that's what he was referring to - the single terminal green connector by the battery that you ground when checking CEL codes, adjusting idle and timing. When grounded, the ECU inhibits the BAC from messing with idle speed, which you'll need to check/adjust idle or base timing.

I ended up with the Cosmo AFM by accident and many years ago. My original turbo swap was done by a shop in Indy, AIM Tuning. While getting parts together for the swap I bought off eBay what I was told was an turbo RX7 AFM. I didn't know any different till many months later when the swap was completed. By then I couldn't go back to the seller so I used it. I've been using it since oh...about 2008 or so. No issues...well till now :P

At one time you could read the part # and that's how I verified it's a Cosmo, but now that sticker has been worn down quite a bit.

Thanks for the heads up on jumpering that, this is the first I've read about it.

Here's the update and it couldn't happen in anyone else's build thread than mine.

I test my AFM and find that the IAT sensor within it is dead to the world. I have a spare N350 so I test it as good and pop it on. It's like night and day. Idle sounds much better. After a mile or so drive afr are sitting at 11.7 or so. I'm all happy and take it out for a long drive of blissful thoughts.

And then I burn up my EGI fuse a mile from home. I tried swapping bigger fuses just to get it home and burned up all of those. I ended up towing it home. So now I have to find my short. I've always been suspicious of the electronics in this car...and now I have some confirmation on it.