UnderPSI

I am going mad chasing this problem and decided to post up and see if anyone has suggestions.
2001 Miata Base. Possibly relevant work includes deleting AC, PS, new engine mounts, Qmax reroute, Supermiata clutch/flywheel, 5XR Radio delete, new clutch master and swapped brake booster.

I have been getting the car ready for this seasons track events and went to fire it up and had no throttle response. Scangauge showed 0 TPS signal and high idle (1300-1500rpm). Tipped the throttle and it will oscillate the RPMs with no TPS signal. Associated DTC as P0123 TPS voltage too high. Also getting p0037 but I am not running a cat or a defeat device to remove the DTC light because basically every light is on (car is a track car so also no air bag or seat belt as I have 6pt, hans, bucket seat, roll bar)
-Busted out the multimeter and wiring diagram with the following results. 5v power to TPS, EGR boost sensor, IAT, ECT. 12v to both 02 sensors. Continuity for all associated grounds, less than 1 ohm or so.
-Tested the signal wire for TPS and it is outputting proper voltage at closed and WOT, 0.6v closed and 4.2V at WOT. No jumps or dips that I was able to discern from opening and closing the throttle slowly by hand.
-Went to the junkyard and grabbed a TPS for giggles with no resolution. Both TPS sensors are outputting acceptable voltage ranges. Worth noting that if I mash the throttle I will finally see some TPS output on the Scangauge while the car is running (something like 17% with an estimated 50-60+% pedal input).
-Purchased an elcheapo Duralast TPS with same results as original OEM and junkyard OEM TPS.
-Curiously tested the ECT output signal to the dash, wire C on the connector. Result was continuity but 70ohms. Checked the engine grounds and cleaned them with scotch brite. No change.

My next plan of attack is to the test continuity from wire C on the ECT (violet/white) to where that section of the harness plugs into main harness at the front of the engine and also from this connection to the instrument cluster. I didnt see any obvious signs of damage in the loom under the hood or dash but it is very possible I damaged something while replacing the engine mounts/clutch/coolant reroute at the back of the engine and also under the dash near the ECU when I replaced the clutch master/booster.

Another thing to mention is the fuse block under the hood with the main has some corroded but not visibly tripped fuses (green/white corrosion). Figured wouldnt hurt to replace these fuses as well.

I really hope I am just a meat head and I pinched something because this is getting pretty exhausting. Car is all back together and aligned, ready for break in miles. First track day is April 17... any help is appreciated.

UnderPSI

After testing for open circuit and short to ground in every single wire without finding any issues.... I finally did the easiest thing and replaced some fuses. Engine runs and idles down to normal and I have TPS signal back to the ScanGauge. I am able to get 1,5,10% etc and hold without the car throwing DTC and no pending codes. You can see in the picture I wasn't able to get the two 30A fuses for the fan and blower as they only had 1 in stock. Consequentially, when the water temp had risen to 200*+ the engine idled up to about 1200 RPM from 850 but the fan never kicked on. I have located two more 30A fuses and I am going to pick them up after work today and will report back.... I am cautiously optimistic.

emilio700

iTrader: (3)

If you have altered the wiring harness or OEM strain relief near the throttle body, you might have a broken wire. Intake mods usually a cause of this. If a wire in the TPS harness is broken, it's usually right at the connector. Easy diagnose is to watch TPS signal live and wiggle wiring.
If it is a broken wire, repair and adds some strain relief. You never want the weight of the harness bearing on the connector. It will hinge there and break the wires, usually an intermittent signal dropout that's hard to isolate and diagnose. Heat shrink or (ghetto) electrical tape to stiffen the harness as it exits the connector then a few zip ties to keep things from bouncing around.

Or it may be something else entirely..

UnderPSI

Thanks for the input, Emillio! Turns out I know myself too well and I was indeed a meat head.

PSA: Please take your time and do not rush, it usually takes longer that way... it would appear that in my haste I damaged the water temperature sensor connector. I had confirmed continuity and 5v power to the sensor but I was under the dash at the PCM connector and a helping hand was touching the lead to the terminals at the connector. He must have pressed the lead into the connector in a way that restored partial contact to the sensor which resolved the short to ground without knowing. We determined the sensor/connector wasn't the issue initially because the readings were accurate but my helper is not an experienced eye for detecting my nonsense. However, I noticed the temp gauge in the dash was acting erratically during a test drive and this was the BINGO moment. Attached is the picture I took shortly after my revelation. Again, this was AFTER it began working so I can only imagine how bad I mangled it before when it was in limp mode. Connector pigtail is in the mail, my tail is between my legs. Keep posted for more adventures of self inflicted misfortune!


DOH!

UnderPSI

I was able to replace the temperature sensor connector and the car seems to run the same as it did when I bent the old connector pins back to make contact. My only issue is the dash still doesn't work (I am aware the dash gauge is separate from the ECU input). I used a digital temperature scanner at the coolant reroute and just below the rad inlet. Seems to be a few degrees hotter at the rad than the ScanGauge reads. Seems to run and drive fine although it doesn't seem to shoot right back to idle RPMs when coming to a stop. Its only been a few dozen miles of test and I haven't driven the car in roughly 6 months so hard to tell if its operating completely normal. I am probably overthinking this now, but its still unnerving.

Would it be worth trying to replace the ECT sensor? Would the ECT sensor to dash fail while the ECU output still functions normally? In other words, could the sensor fail to output the dash reading and still be 100% operational as far as the ECU is concerned (No CEL or pending codes). The wiring diagram shows the dash pin goes straight to the dash and is also grounded. Would I have fried the dash gauge itself? Its seems to flutter on start up and then go stone cold. Very weird and confusing and I cant help myself but overthink this.

UnderPSI

I know this has been a very weird and specific issue that probably isn't adding a ton of value to the forum but I still wanted to follow up on this just in case it happens to help someone.

After repairing the connector I took the car to its first track day a few weeks ago and it ran great. The only lingering issue was a slightly high idle but would drop to normal when I pressed the clutch in. My guess was that I plugged the transmission neutral switch in backwards and was causing the high idle. When I checked the connectors they had substantial corrosion so I tried cleaning them first without resolution (picture below). I then swapped the connectors and the issue has been resolved! The water temp gauge in the dash seems to be working although not as it once did (likes to dance from time to time). Considering I can still monitor the temps in the ScanGauge I will leave that to tinker with when I have a lull in track days.