This is the continuation of the lumpy idle and stalling problem! (see previous posts for the story so far…) I have fitted a second hand TPS from MX5 Heaven which is sold as tested and working. I’m using the test procedure in the Veloce Manual page 5:31 but I can’t get continuity between pins A and B as specified in the manual (on the new or the old switch) or between any pins at any point in the rotation. Is the Manual definitely correct on this test and set up method? I’ve fitted the thing anyway with the sensor in mid slot position and the car runs better but still stalls, now instead of hunting first it just stalls dead so sort of progress! Really need some help with this, it’s spoiling a great little car!
With the sensor unpluged you should have continuity between 2 of the terminal on one end with the throttle fully closed. It’s hard to describe with 2 in words, would you know what I was refering to if I said the connetor has 5 ribs (2 on 1 long side, one on either end end and 1 on the other long side) on its outside that mean the connector can only be plugged in one way round.
Thanks Robbie, I do understand your description, it’s very well illustrated in the Veloce Enthusiasts Manual. Have you actually conducted this test yourself? I was just trying to see if my testing method was at fault (I’m pretty sure it’s not, I am a trained electrician!)before I bung the part back to MX5 Heaven! Cheers, M
The position of the sensor is critical. Test it with it fitted to the engine then adjust it in small increments until you get continuity. Are you using a method that uses 2 thicknesses of feeler blade?
Robbie, thanks for coming back. Yes, that’s the way I’m adjusting it but the problem at the moment is that I can’t get continuity anywhere on the sensor, either on or off the car so I suspect that the original and the replacement are both faulty. In your experience, do the stalling symptoms point to TPS failure? Opinions (naturally!) seem to vary quite a lot!
Thanks, Mark
I personally have never come across it, I’ve never come across a faulty TPS either though. If the TPS is faulty then stalling may be a possible symptom. I would have expected more symptoms than that though.
Check for voltage at the 4 terminals with the sensor plugged in and the ignition on as you open and close the throttle. What voltages do you get?
Aside, the Mazda WSM says to check continuity between terminals C & D. If you lay the sensor flat with the single rib up, terminals C & D are the 2 on the left.
Have you adjusted the throttle stop at all?
Robbie, thanks again, I will do all that. It’s interesting that the Mazda WSM says continuity on pins C & D as the Veloce Manual says A & B! The throttle stop had been “adjusted” by a PO who had also fitted a K&N, which I have replaced with the original filter and box. I’ve reset the throttle stop to .35mm clearance as that seeems to be what is implied but not specifically stated in the Veloce manual. I’m working a long shift from this evening so won’t have a chance to do anything until friday but will post again then. Many thanks, Mark
There is no measurement for the throttle stop, it’s factory set and shouldn’t be adjusted. That may be the cause of intermitant stalling if that’s the issue you’re getting. Does it stall if you come off a wide throttle and are also on the clutch? Roundabout approach for example. I have a theory that if the throttle butterfly is adjusted too closed (poor English), then the idle air control valve can’t respond quick enough to the sudden shut off of air.
No, this is stalling at idle, sometimes from cold, usually from hot. Hunts first then stalls, no clutch involved. Runs lumpy at low revs too, hence my thinking about TPS. Have done all the other stuff already, and reset base idle every time, no change. What about O2 sensor? I also have a set of coils to try, done HT leads already!
Thanks Mark
Have you considered the engine coolant temperature sensor? Have you checked for DTCs?
Robbie, sorry for the delay, real life does get in the way of workshop time! I have tried fitting both the new and old TPS. I have discovered the correct test procedure, the Veloce Manual has the connector pins labled the wrong way round and says you can use a battery/bulb continuity tester; you cannot, it needs to be an ohmmeter set to 1Kohm. Have refitted original TPS unit, initially tried setting throttle plate .20mm open, (as per your theory,) set TPS as per manual, runs but revs up repeatingly. Reset plate to .05mm, better, but idles at 1200 rpm. Set plate shut and better again but still stalling even after base idle reset. Will try setting dial gauge on throttle plate (butterfly) to get exact point of lift from closed and try once more but am now thinking it’s not TPS. I have got diagnostic codes, this gave me TPS, O2 sensor and a code 11 which I can’t find anywhere. (funny thing, had the same code 11 which didn’t appear to exist on a Nissan of similar vintage once!) I have a set of coils which I might try but it really doesn’t feel like coil failure to me. We will get it to Billing even if it’s still sick!
Cheers, Mark
Robbie, it was good to meet up at Billing and run through the problem. New Readers may need to know that Robbie pointed out I was working to the pre-1996 diagnostic codes and with this new information I started again. Code read MAF sensor so returning to that (I had felt it was the problem all along,) I discovered that a previous owner had cut and lengthened the wiring, probably to fit a sports air manifold. The kit seems to have included a new well made extension loom with crimps for the customer to fit but these had been poorly made where inserted into the car with several dry joints. The whole job had been finished off very similar to the original Mazda wiring so not easy to detect! A session with the soldering iron and some heatshrink tubing remade the loom and now it runs and idles as it should. Fuel economy greatly improved too! Many thanks to Robbie for all his help, and another possible fault added to the log! Now on to sill repairs…