Mods beat me to it damn.

 

Alright I'm finally starting to run out of patience with this car of mine. I just can't for the life of me get it to hold an idle at all. And worst of all after all my reading I'm starting to run out of things to check out.

The way its going now is that if I start it it will idle on its own (at about 1500rpm exactly) anywhere from 10-30 seconds on its own and then all of a sudden no sputtering or anything it just cuts out and dies. But I can keep it running if I'm quick on the throttle and get it back above 1000rpms quick enough but then once I let off the throttle it dies again.

So far I've checked vacuum leaks at least 5 times getting none each time. I've checked my spark with a scope and its still getting spark as it dies.

I've checked injectors with a scope and they also are firing as it dies.

Checked fuel pressure as it dies and it stays consistant. I've checked and recheck the AFM at least 4 times and the connections there are good.

Now I have my throttle body off just checking the clearance of the bottom throttle plate and cleaning it up a bit to keep myself amused so I don't hang myself.

And for what its worth its a stock N/A with the aux sleeves removed and single 2 1/2" header back exhaust, about 1000ish miles into the breakin of the rebuild.

 

Sounds like a bad/ unpluged AFM. Have you tested it all the way back at the ECU?

 

Or a vacuum leak.

 

Like socalrotor said, check the AFM from the ECU. I had the same problems a couple years back when I first got my FC. Took the wiring harness out completly to install new engine and somewhere along the way three wires in the AFM wiring bundle snapped.

You problem is almst for sure that.

 

There is no way that its a vacuum leak, I've went over the entire engine multiple times with various different methods to check it, propane, vac. guage, smoke tester etc.

I haven't tested the afm all the way back to the ecu yet, but with a bad afm wouldn't it die regardless if I gave it some gas as it was dying or not.

Oh another detail, it runs strong as soon as its doing highway driving with no trouble, but as soon as I bring it to a stop it dies.

 

BAC valve stuck/clogged. Have you checked the BAC?

 

The most I have checked with the BAC valve is unplugged it and tested its resistance (which was good)

 

I dont know about the light throttle and keeping it running. You are right, the car dies regards less if AFM is bad BUT who knows what happens if only one or two wires are FUBAR. maybe above 1000rpm something "magical" happens.

Best bet is just to check from ECU. I know it is frustrating and tedious but this is part of troubleshooting; check everything regardless.

 

Ok so what you think is the best bet to check it is to have me backprobe into the ecu pins with my multimeter and have somebody start the car to see if the voltages are good as it dies, or just check the key on voltage at the ecu?

And I don't have a problem with doing the tedious work itself, its just when you get started on these tedious jobs hoping to find something but nothing paying off and getting that sinking feeling of failure haha.

 

Alright I went through all the Input pins on the ecu for the afm, and they all check out and stay constant from the time it starts until it dies.

But for my trailing coils and ignitors I have a voltage ranging from 1-4 volts with the key on the on position. The Pin numbers on my diagram are M and U which are second from the left and the sixth from the left, both on the top row of the largest connection on the ecu.

But other than that everything seems to be in order at the ecu. Still trys to idle at 1500-2000 rpm but dies ten to twenty seconds later,.

 

if its really givign you this much trouble and you can't figure it out...........just bump the idle stop screw in until it idles at 1200rpm or so. You'll waste alot of gas but you'll be able to use the car.

FWIW though I'd re-check your TPS, remove and clean the BAC and verify there's no vac leaks (yes, again) with the carb cleaner method. If its a new rebuild and has done so from the start I'd suspect a leaky gasket from an improperly installed/toruqed manifold.

 

Thats the problem, it tries to keep an idle at 1500 to start with. So just bumping the idle doesn't help at all.

I'll try to explain exactly what has been going on and then try to do some more reading and see if I can think of anything else to try out on monday.

Okay here goes my explanation of my situation, so when I start it up its in neutral and my foot is off the clutch. Then I crank it, it starts and the revs go up to about 2000rpms and hold there for a few seconds.

After that it slowly starts to go down almost like its trying to slowly drop it to and idle. But as soon as it drops past 1500 it falls flat on its *** and dies. Unless I can give it some gas before it drops below a certain point as I had mentioned earlier.

 

Also another weird thing that I found with a scope hooked up to the trailing coils is that I don't have much of a spark on it. Like if you compare it to the patterns found at the bottom of this page.

http://www.teamfc3s.org/info/articles/demystifying.html

It's nowhere even close, my pattern is just a straight line with a little firing line on it and that was all, I don't recall the exact kv's of it but it definatly wasn't high.

 

also check your pressure sensor

 

thats already been checked

 

No no. I don't think you understood my suggestion.

The idle set screw is an adjustable stop for the throttle. Meaning if you screw it in enough, it will mimick holding your foot on the gas. It will actually hold the throttle open......or rather, it will stop it from closing all the way.

But I'd go back and double check everything I'd even go so far as swapping in certain parts. If the AFM checks out OK - swap in another one just to see. The TPS checks out fairly decent? Try another one just in case. and so on....

 

That sounds like an plan, I've already swapped tps's without any luck but I'll try and find a AFM to see what happens then but I have the sneaking suspicion that it won't change anything for me.

 

Time for an update...

Checked my back valve operations this morning and it all checks out, The valve opens and closes with volts, and the connector is getting roughly 9 volts at idle.

I also re-set my timing by finding TDC manualy, with the information I found here, centering a rear apex seal between leading and trailing plugs on the rear rotor. Seemed to help the smoothness of the idle but it still died shortly after start up. Although it was easier to bring the revs back up as it was dying off.

Gonna check out my CAS, Leading and Trailing primary coils on the scope after I get the BAC on tomorrow morning then RE-check the tps again.

Just out of curiosity, which pins of the LED diagnostic connector hook up to which wires on the TPS check connector, the check connector is removed so I'd like to rewire a new connector from the ecu to set my TPS that way rather than with a DMM.

What else you guys think would be beneficial checks to do know, since I have access to a scope which I've been finding to be very beneficial.

 

Alright I'm officially running out of ideas of Sensors that I can check out. And now I'm starting to wonder if it could be the ECU itself thats fried. Is there a way to check the ecu to tell if its still doing what it should be?

Refer to this thread for what I've done thus far https://www.rx7club.com/showthread.php?t=637187

 

Threads merged... only start one thread per subject per member

 

You really didn't do much to chech the bac out. Not much at all.

You have a scope/meter and should have been able to look at it's duty cycle.

No meter? no scope?? Not a big deal. Remove the air filter. Turn the key to ON, engine OFF and listen for the pulsing of the bac. About 120hz or so. Can't miss the pulsation.

Or remove the bac. Only two nuts. Key to ON engine OFF and look at the bac vibrate.

Bac good??? Well, let me put it this way. You should be able to pull the plug off the bac and the engine should idle. Not idle that way???? Set the timing with a timing light and the rpms under 1000rpm. If a turbo, turn the bacs idle screw til it idles higher or where it needs to be i.e. close to 750rpm.

If a 87or eighty six, then maybe turn the variable resistor to increase decrease the idle. The FSM gives clues how to do that.

In the FUEL secito of the FSM there is/are pages that show the value of each pin on the ECU at idle and with the key just to ON. Only takes maybe a half hour to do them all.

Vacuum hoses in the wrong place can cripple you. Not all nipples on the throttle body are vacuum. Only a couple. Make sure they go to the right places.

If a n/a car, series four, make sure the two vacuum lines on the front of the throttle body are not crossed. One is vacuum, the other not vacuum. ***** the idle up.

Trail coils never did squat for idle. Forget this train of thought. Unless the wires are corssed on the trail coil/plugs.

With a fully hot engine check the output wire of the tps connector. The green/red wire on the harness side of the TPS pigtai. Plug connected up. It should be one volt dc. If not,then screw it til it reads that. HOT engine adjustment only. NO foot on the pedal. This can be done even if the engine dies. Just leave the key to ON.

 

Yeah, I've went through the BAC with a scope and tested for duty cycle, and it was goood.

And I can't set the timing with a light because as soon as the revs start to drop below 1500 rpms it dies out.

I have checked all the pins at the ecu again today and everything checked out, aside from a few small things. I don't recall exactly which two but the coil and ignitor checks for the trailing where getting volts with just key voltage, (the specs were 0v - key on for both, then one was 0.8v idle and the other 1.?v idle I believe) at idle they were good, but with key on one had 1v to it and the other had 3v to it.

Does anybody know just how these two pins have anything to do with the TPS setting, I was looking through a wiring schematic and they go to the check connector used for the tps, but the tps itself has nothing to do directly with that connector.

Then there were the tps checks at the ecu, the throttle sensor itself was good 1v idle - 4ish volts wot. But the two emissions solenoids linked to that had 0volts where it should be 2 and the other was .6v where 12v should be. Pins 2O and 2P I think they where, one was def. blue/red the other I think was blue/yellow?

The vac. lines at the TB are not crossed the top two are capped because those systems are gone, and the bottom runs to the p/r.

I figured the trailing coils wouldn't be the root of my problem, the only reason I was checking there was because one of the instructors was once a mazda tech. and he was thinking that maybe something weird was going on there. I was wary of it doing anything but I thought I may as well check them to keep him off my back.

 

When the TPS is set right and the engine is hot, the Relief solenoid should be energized which in turn means the pin 2P is putting a ground on the Relief solenoid and pulling the voltage down to less than 2vdc.

Just the opposite with 2O. Not engergize at idle with a hot engine so it reads the 12vdc on the black/white wire on the Switching solenoid.

The tps check connector is????????????? a test connector or check connector if you will. You check things out with it i.e. the state of the ECU output to the Relief and Switching solenoids.

There's something basic wrong with a engine that won't maintain an idle below fifteen hundred rpm. Like a huge air leak.....injector plugs on wrong.....that type of thing. The type of thing that can't be fixed on a forum.

 

Yeah, thats why I'm here though, I don't have a huge air or vacuum leak. If by injector plugs you mean the plugs with diffusers that go under the injector they are in right. And the injectors are sealed well to the rail and block also.

Now what if either of those solenoids where removed with all the other emissions stuff, and their wiring removed down to the check connector.