imloggedin

heres what my idle is doing. http://www.unrealweb.net/RX7/idle.MOV it just goes up and down and up and down. when i rev it and let off the pedal, when it comes back down it almost dies usually, then the rpms pull back up.. upp and downn up and downn. so i checked the fuel pump voltage cause i undid the fuel pump rewire (please no one say anything about the rewire) and put it completely back to stock and soldered every connection. well the voltage is at 12v at idle now.. makes no sense, and yes it IS hooked up right. i checked my alternator belt and its slipping pretty bad, so i know that needs to be fixed with a duel pulley probably.. because i have adjusted it many times and i have no air pump. when the rpms go down the voltage on the fuel pump drops. my question is, would the slippage of the alt cause the voltage on the fuel pump to drop or is that normal when rpm's drop? and to test if the ECU is making signal to the relay/resistor wich wire do i check on it and what do i use to check it, what signal does it send to drop the resistor to 9v? (HAILERS, if you can id like a response from you on that). i will check my tps soon but i havent had a chance today, i just replaced it and adjusted it a few weeks ago so i dont suspect that, cause it ran fine after. kind suggestions are appreciated

NZConvertible

That's almost always caused by idle speed being set too high and/or TPS not set right. With the idle speed so high, the ECU over-corrects to drop it, then over-corrects to raise it, and gets into a big nasty loop that is very embarrassing at traffic lights...
Look at the wiring diagram on page 50-34 of the FSM. It's a pretty simple system. The ECU provides a switched ground that opens the relay, forcing the current through the resistor, dropping the voltage. Check to see that putting power to the relay's coil opens the contacts.
I doubt it's slipping at idle, because if it was there's no way you'd get enough charging or cooling under normal driving. The electrical system voltage is always a bit lower at idle, and increases as revs increase. That's normal.
See the FSM page 4B-33. Check ECU pin 3D (green wire, red stripe). 12V with the ignition on; below 2V at idle.

imloggedin

it is slipping at idle.. trust me i checked.. can that be causing my problem.. making the voltage go up and down.. and does your voltage to the fuel pump go up and down when your rpm's do usually?

ShadowX

My does the exact same thing, except that it idles a little bit higher. I'm replacing the ECU just for the hell of it, I'll update when I get it.

NZConvertible

It's possible, but I can't see how the car can be drivable if it's slipping at idle. You'd have no cooling or charging at higher rpm when the load on the belt is a lot higher. Anyway, if you think it's a potential problem then eliminate it. Just tighten the belt up. You don't need a dual-belt alternator to stop slipping at idle.
I can't exactly remember my own measurements, but the voltage of the entire electrical system is lower at idle, and increases when you rev the engine. Alternator output is roughly proportional to revs. How much up and down are we talking about here?

HAILERS

Yep. 3D pulls the relay in and puts the resistor in the circuit and makes the voltage drop at the fuel pump...down to 9 or 10 volts.

A real low idle could cause the fuel pump voltage to drop a few volts. That's not unusual. What is unusual is the slipping alternator belt, even if the airpump is disconnected. At idle it should not slip. At high rpms you'd expect it to slip without the airpum being on there. I've noticed in the past if the battery voltage is way low and the alternator isn't putting out like it should...that for a few minutes the engine will act up so to speak til the alternator gets the battery back up to 12v.

Something is wrong with something said here. IF the idle has been set to LOW....that is what will give you an up/down, up/down, up/down idle. The idle NEEDS to be set with the initial set coupler installed or the bac plug off....as close to 750 as possible. And the reason for this being so, is so that after everything is plugged back up and running normal and the idle drops down to its lowest, the lowest will be near 750rpm. That way the bac does not have to make radical corrections to keep the idle speed at 750rpm...

If your REAL IDLE is say 400 rpm, and you remove the initial set coupler and put the bac plug back on (only if you took that step) and now drive the car and say you come to a stop sign and the idle drops down, it'll drop to the 450 setting and the bac has to work its *** off trying to get it back to 750rpm. It'll overshoot the 750...drop below 750....drive it up or over 750...and on and on for a short period.

I'd bet money the rise and fall of the fuel pump voltage has little to do with the up down situation. I think its a voltage problem due to the belt slipping and the battery not being fully charged.

And the up down also has the traits of a small air leak somewhere. I went for the belt though, so I'll stick with it.

imloggedin

thanks for the responses hailers.. and thanks for being nice NZ

first thing ill try is the TPS and tighten the belt.. its just been sooo cold here alls i can do is speculate without touching my car :X

HAILERS

Ah ha. Cold weather! If the tps is not set right AND the thermowax/fast idle is not set right....that could be part of the problem. Set the thermowax/fast idle prior to setting the tps and always set the timing with a fully warm engine .