El Conquistador

So my car has been having an issue where the idle would surge in neutral with the clutch out, but would calm down once the clutch was depressed plus there was a P0850 code. Looking around on here, I saw several instances of people having the same issue and it always turned out to be the neutral switch, which makes sense. So I ordered the switch online and reading about how difficult it is to get to, I took it to a local rotary shop to have them put it on.

Well when they lifted the car, they noticed that a couple of wires near the transmission had been severed, likely the wires going to that switch. They spliced them back together and you would think that was the end of the story.

They fired it up and it still did the same thing. They checked the resistance on the switch and it was indeed changing when shifted. Just to be certain, they connected the new sensor and pushed the button in by hand and it made no difference. For the hell of it, they slapped in a factory airbox in place of my aftermarket one and there was a slight improvement, but not much. I have the original and will likely swap it back in when I get a chance.

It got a little worse after leaving the shop. I'm guessing they not only reset the codes but also the PCM as a whole. The car stalled out on me three or four times on the way to work when I pushed in the clutch. I'm guessing it had learned to compensate for something until they reset it. So now it surges in neutral with the clutch engaged and sometimes stalls when the clutch is disengaged. The only codes that reappeared after about an hour of driving are P0171 and P2270 which, if I'm not mistaken, are probably because the car has no catalytic converter.

There were at least three technicians who work on only Mazda rotaries who looked at it and couldn't figure it out, although in their defense they only had the car for about three hours because I needed it to go to work and only planned for a quick sensor change. So I'm turning to you guys.

I ordered an Ultragauge and looking at the tracking, I think it's waiting on my doorstep right now, so if you need any more information that it can provide, let me know. I don't yet know everything it's capable of.

logalinipoo

Did you recently have any work? Like a engiine swap? Put it in reverse and see if your reverse lights work. Or maybe if they are on in neutral or another gear.

El Conquistador

I just bought the car last week. Somehow it worked fine when I was testing it out. The shop said it looked like the transmission had been opened up so it was likely rebuilt.

Assuming the key only has to be on and the engine doesn't actually have to be running, my reverse lights aren't working in any gear. I'm not sure how that would lead to the surging, but I have a feeling I'm not going to like your explanation.

logalinipoo

There are 2 transmission switches. One for reverse one for neutral. The plugs are interchangeable. They might be swapped out.

El Conquistador

I'll check again but I'm pretty sure the reverse lights didn't come on even in neutral. That gets me thinking though that maybe neither switch is getting power due to a loose connector or a blown fuse or relay. Any thoughts on that?

logalinipoo

Maybe one of each wires are plugged into each switch. Ie

Neutral should be wire a, b and reverse c,d

You might be neutral a,c and reverse b, d

El Conquistador

I checked again, no reverse light at all.

logalinipoo

Ok does cruise control work?

logalinipoo

Crap 0171 is your car is too lean. Its a vac leak or front 02 sensor m aybe. Its not because of your midpipe.

El Conquistador

I figured it just went along with the other code. I'll see if I can find any vacuum leaks. Why would it change when I push in the clutch though?

logalinipoo

Less load on the engine

El Conquistador

I found a large source of unmetered air. There's a massive plug in the intake tube under the dipstick that fell out. Luckily it didn't fall far. It doesn't really look like a factory item, like it may be something they put in with the aftermarket intake.

In any case, I drove it about 20 miles, it idled better with the clutch in, and it didn't throw a code, but it still has the surging in neutral. You may be right about the wires being crossed. It would be a lot easier if I could read what signal the PCM is getting from those sensors.

El Conquistador

I had an epiphany. I'll pull the connector off the PCM and check the resistance of what should be going to the neutral switch in different gears. The PCM in this car is so much easier to get to than the last one I pulled. I doubt I'll get to it today but I'll post the results when I do.

Am I right that pulling the fuse for the PCM is sufficient to make it safe to pull the connector? I don't care to reset my radio stations and all that jazz yet again.

I really appreciate the help so far.

logalinipoo

A jack and 15 minutes and you can check the switches directly. A couple of alligator clips and a multimeter you can sit in the driver seat and test see if its working or not.

04Green

iTrader: (1)

If you solved unfettered air issue, your fuel trims are likely way off.

With a cold engine, 20 brake stomp, start, let it idle 15 minutes..

El Conquistador

My car is lowered and it would be a big pain in the *** to jack it up compared to pulling the PCM connection and hooking up the multimeter. Plus it would hint at a loose connection or broken wire if it's an open circuit in neutral and reverse.

The trims may be off, but the vacuum leak didn't start until yesterday so it's not the main issue. It ran a lot worse when the plug fell out.

logalinipoo

Or it would indicate the plugs are plugged into each other and not the switches at all.

El Conquistador

Maybe, but at least I'll have a reasonable idea before I go in. I'll likely rent a lift to work under the car.

El Conquistador

Looking in the schematics, I found a connector C-19 through which the reverse switch circuit travels but is easily accessible in the fuse box under the hood. I jumpered the reverse switch out. I turned on the key and still had no reverse lights. At this point, I was having trouble imagining what it could be except the bulbs themselves, so I checked in the trunk. As it turns out, both lights were unplugged. Why? Because when they're plugged in, the lights come on when the car is in neutral.

It just never dawned on me that someone might have had the reverse lights in neutral issue and unplugged the lights as a hack fix. I'm thinking maybe I should have inspected this car more thoroughly before I bought it...

I think the case is closed on this one.

logalinipoo

Well yes, 4 things to look for on a vehicle. Lights, leaks, leans, and lot lizards.

But that makes me think you might have a replaced engine so that might be a plus.

El Conquistador

Not the engine but rather the transmission. I found the first owner on here and a post where he said he broke a shift fork and the dealership said the car was abused (which he denied in the post, so who knows...) and wouldn't cover it, so he replaced it with an 07 transmission. The shop told me that the VIN on the tranny matched the car, but it looked like it had been opened up, so I'm guessing at some point it was rebuilt and put back in the car.

Whoever did it must have plugged the switches in backwards and couldn't figure out why the car idled poorly and the reverse lights came on in neutral, so they unplugged the lights and sold the car. (I'm not sure why the car idled so well when I first looked at it. Maybe he unplugged the clutch sensor.) They also did a poor job with the rebuild because the first gear synchronizer is in bad shape. All the other issues I've found are cheap to fix and are worth it for how cheap the car was (I was informed about some of them), but the synchronizer issue not so much. On the bright side, the interior and exterior are in superb shape and it already has some mods I was planning on doing.

At this point, all I can do is fix one thing at a time. I can say I now own one of my dream cars.

logalinipoo

Good luck and i with you the best. As for first. Try bleeding the clutch. It might be that or a bad clutch bracket.

I would normally put the bracket first but since you think you have a newer trans it may have been done wrong.

Get those switches swapped and let us know how it goes. Research the clutch pedal and bleeding. The pedal is a little hard to see when it starts going and bleeding can be very difficult.

El Conquistador

I don't think it's the clutch, but I'll try it anyway since it's a lot cheaper than a tranny rebuild. If I shift directly from neutral to first at a stop, there is sometimes a little grinding. If I shift to second to stop the input shaft from spinning and then first, it never grinds. Downshifts to first are worse even though I've formed the habit of double clutching and rev matching on downshifts to save synchronizer wear on a previous car that was known for having weak synchros. I've read on here about a technique for smoothing the synchronizers but so far it hasn't helped. Also, I had my gear oil changed while at the shop.

logalinipoo

Yeah that sounds like the trans. If you can put it in other gears at a stop.

dannobre

iTrader: (3)

Quit trying to shift into first when you are moving...there is no reason to do it and it is hard on the transmission.

If you are at a stop with your foot on the clutch...and it is still difficult to put into first because imput shaft is still spinning...check the free-play on the clutch.

With the clutch to the floor there should be no contact between the clutch and flywheel and it should go into gear