Starfox07

So, as some of you might, perhaps (though not likely) recall, my car has been having this occasional low-rpm hesitation/miss. Doesn't happen that often, but often enough to be irritating.

Symptoms:
-Loping idle (literally sounds like a bridgeport, which is cool, but definitely not normal)
-~3k RPM hesitation/miss. It will stutter and refuse to rev until it clears 3,000, and then it feels perfectly fine.

That's really the only two issues.

The car never floods and the fuel mileage is about on par (a little below) so I don't believe it is fuel-delivery related.

Additional info:
-Replaced cap
-Replaced rotor (^ < both were worn, but not excessively so)
-Cleaned plugs (they looked largely fine after 2.5 years by the way, no evidence of rich or lean conditions, again pointing more towards ignition than fuel)
-Ignition leads/Spark plug wires are fairly new

At this point I'm thinking it's one of the coils. How might I test them?

jonjonwells

Just swap coils. If it is a coil that is causing this, then it is the leading coil. Swap them and see what happens.
I am having a hard time seeing a coil doing this.... possible.. but unlikely.

You can run without the trailing completely and not have this issue.

Twilightoptics

iTrader: (1)

Sounds like weak spark and fuel loading up in the intake/combustion chambers and doesn't clear up until reved up and out.

OR a vacuum issue.

What is your idle voltage AT the coils?

t_g_farrell

iTrader: (1)

Get rid of the stock ignition and go DFIS. Theres lots of flavors, you can pick and
choose what you feel comfortable with.

It sounds like maybe you have an ignitor going bad. Theres a section in the FSM
on testing ignitors you can follow. Note that a lot of ignitor and coils issues hide
when they are cold and show up once things get hot under the hood. Sounds like
you covered the basics with new cap, rotor, wires and plugs.

Make sure you have a good ground to the engine. That can be an issue as well.

Starfox07

About the vacuum leak.

I've got a low idle (600rpm or so, sometimes slightly lower) and that is with the idle screw all the way out. So I wouldn't eliminate that from the possibilities.

To 'swap the coils' can I just swap the leads and not have to unbolt anything?

t_g_farrell

iTrader: (1)

Yeah, you can do that but sometimes the leads don't always reach. Its actually
easier to unbolt the coil bracket and physically switch them. In either case take
some pics or label the wiring so you get it right the first time.

Twilightoptics

iTrader: (1)

If you have to have the idle screw all the way in, you've got something else wrong. Super bad ignition, huge vacuum leak, etc.

Starfox07

No, it's all the way out

Perplexing kind of.

Twilightoptics

iTrader: (1)

You should be idling at about 750rpm. If the blades are too far closed, you may not be working the idle circuit properly.

Screw that screw in to achieve the 750RPM idle, then set timing. Then readjust idle if it changed.

Starfox07

Ok. The car idled perfectly until I took it to a 'rotary specialist' (not naming names)

He:

-Lied about auxiliary ports working properly
-Improperly installed brakes (no anti-rattle clips at all)
-Engine didn't run properly at first
-Engine still doesn't idle properly

Basically I'm doing all my own work now.

More fault finding:

I noticed that the battery terminal connector was pretty old and fatigued (aka even all the way tightened, it wasn't really clamping the battery post), so I unbolted that and I'm going to get a new one. I unbolted the chassis ground that attaches to the driver-side strut tower and cleaned all surfaces with a wire brush, then re-attached it. Next up is swapping the coils.

If after all of this, the issue is still there, I will probably check/replace the ignitors and re-time the car. I'm not entirely sure the timing is right, seems like it could be a bit retarded

Starfox07

UPDATE

After cleaning the chassis ground, replacing the battery terminal connector, and swapping the coils, it....it...it!!...it runs exactly the same. No change.

Next up: Ignitors

There is a useful information in the FSM concerning this, correct?

Video to illustrate both the low idle and the loping at 1,000rpm
[youtube]http://www.youtube.com/watch?v=T-QSmLi3Heg[/youtube]

rotordogg

iTrader: (4)

Is this an SE? Did you adjust the TPS? Not only adjust it, but check the resistance as you run the plunger to make sure there are not any dead spots. Mine did the "looping idle" until I adjusted the tps. In fact, while it is "looping", turn the TPS adjust screw counter clockwise and see if it clears up. It should start looping faster and faster until it is a steady idle.

If it's a 12A, forget everything I just said.

Starfox07

It is indeed an SE. I will try that tomorrow, thanks!

rotordogg

iTrader: (4)

You are welcome. The TPS can also cause the drop at 3K rpms, if it is way out of adjustment or if it has a dead spot, it doesn't send the proper signal to the ECU.

In the FSM go to the Fuel&Emissions 13B section and look at page 39. It describes how to adjust the tps.

Good luck!

-Scott

t_g_farrell

iTrader: (1)

So who was the "expert" that helped you with this anyway?

Starfox07

I'll give him the benefit of the doubt that it was a mistake.

Starfox07

Ok it appears I either need a special test light or two voltmeters to test the TPS?

Surely there is another way?

rotordogg

iTrader: (4)

It's the only way, but it is easy. I made a test light with two 12V light bulbs. You can probably use 12V LED lights from radioshack as well. Just wire both positive leads together and leave each negative lead seperate. Plug the negative leads into the two parallel female spade connectors on the green test connector and plug the two positive leads into the top slot. This pic should help make sense of it:

Starfox07

Ok I finally cobbled a test light together. I'm getting one light on at idle. That means everything is ok right?

Starfox07

Got tired of my makeshift test light so I just went out and bought another multi-meter (yes yes, I know its very un rx-7 owner-like)

So with everything hooked up and the car warm, I could never get anything more than 1v out of one of the connections and around 10 out of the other. Is this normal? I brought it to a spot where it was 10 on one meter and 0 on the other. Started it up and it seemed to behave exactly as before. Low but relatively smooth idle, and a choppiness/missfire from 1k-4k and beyond.

I do think there is a dead spot in the TPS, because at one, very exact, position of the throttle pedal will make it surge. edit: Checked it with an ohm-meter, there is no deadspot I could find. Goes from 1k-5k as the plunger goes out just fine.

Can somebody explain to me the proper method of setting the idle? I've read it is NOT the screw on the top of the throttle body, but another hex/screw on the side.

At this point, surely it has to be the ignitor right?