JermsBoo

I just got my 1988 Rx-7 10th AE today.

The car has a problem of a very very low cold idle. When I start it up if I don't keep revving the engine it will stall. When I stop at a light or stop sign it will also stall. After it warms up it idles at 500 RPM. The engine is rebuilt. It needs a tune up. Will that fix this problem?

Also the engine sometimes floods. Is there a fix for that?

Last problem. When I was on the freeway before the car warmed up. I was in 5th gear but was losing speed. So I downshifted to 4th and still losing speed. So I dropped it to 3rd and it accelerated again. I shifted back up to 5th and it did the same thing, but after repeating the above a 2nd time it became normal. I'm guessing engine had too much fuel in it?

Thanks in advance.

beefhole

iTrader: (29)

Any mods? Anything stock removed? Sounds like you may have removed the BAC. A fresh rebuild may need some break in before the idle becomes healthy. Flooding is common.
Not sure about the freeway thing. Sounds like an electrical gremlin...

JermsBoo

Rebuilt Engine With 8xxx Miles
Koyo Radiator
Samco silicon hoses
Magnacor Spark plug wires
Tein Front Sway bar
Tokico Blue shocks
Racingbeat lowering springs
Brembo Cross drilled/slotted brake rotors
hawk brake pads
mazdatrixx stainless steel brake lines
brake calipers powder coated
S5 tailights
GP style full body kit
SakeBomb garage custom Bi-xenon HID projector Kit
rx7.com stage 1 clutch kit

Thats all I can think of right now.

satch

iTrader: (1)

As suggested, the BAC is designed to keep the idle rpm at 750 or a bit above when the engine is under load. Do you still have a BAC or not?

beefhole

iTrader: (29)

Your engine is no longer "rebuilt" per se. 8k Miles is 5x more than enough for break in.

How do your plugs look? How many miles are on them? Have your injectors been serviced?

Again, it does not sound like you have a (functioning) BAC valve.

JermsBoo

The injectors haven't been serviced. I haven't had a chance to take a look at the car. Busy day. I'll check it out and get back to you guys on the BAC.

JermsBoo

So I just went and started the car. The RPM shot up to about 2500. (Complete cold start, didn't start the whole day) I put it in first and the RPM dropped to about 1000. So could the flooded engine been the cause of the car stalling?

Snowburn

iTrader: (2)

It's worth it to have the injectors cleaned.
I had mine done by witchhunter
One injector was only flowing at 77% capacity!

Also, make sure you have clean fuel that hasn't been sitting for awhile...

satch

iTrader: (1)

Was the 1000 rpm reading coming from an engine that was completely warmed up or just after it was started as it makes a difference.

JermsBoo

Just after it was started.

I'll look into having my injectors cleaned.

satch

iTrader: (1)

You need to allow the engine to warm up completely to tell you where you stand.

JermsBoo

Ah okay. Well what I had described before was when it had warmed up "When I start it up if I don't keep revving the engine it will stall. When I stop at a light or stop sign it will also stall. After it warms up it idles at 500 RPM"

I had thought it was a "cold cold start" but I was wrong. So instead of "After it warms up" it is now "After driving for a while"

Could that be because the engine HAD been flooded?

satch

iTrader: (1)

If you still have a low rpm such as 500 after the car is warmed up and stays at that level then you just might want to check the BAC. If you disconnect the plug to the BAC and supply a ground to one of the two BAC terminals and a battery voltage to the second terminal the BAC should click. When doing this remove one of the two wires, either the ground source or the voltage source and do this a number of times to check the condition of the BAC as it should click each and every time the ground and battery voltage is supplied to the two BAC terminals. You can also pull the plug while the car is idling at 500 and see if there is any change. Lastly, with the car idling turn on the A/C to see if the rpm drops and stays there or shuts off or if the idle stays constant at the 500 level.

Snowburn

iTrader: (2)

AFAIK the main residual engine damage from flooding with too much gas is fouled spark plugs.
You can do an easy check and pull out the spark plugs and see their condition.

However, it sounds like you have a problem in your idle system.
You should do the test satch has described.
Of course it's entirely possible somebody has monkeyed about with the throttle screws...

JermsBoo

Well I just went and drove it for a good hour. Came back parked and tried starting it up again. Everything was normal. Normal idle about 750 rpm.

JermsBoo

Okay so another update (I don't think anyone is following this anymore heh) I drove for about 30 mins weather was 90s. I got to where I was going went in for maybe 15- 20 mins. Came back out and started it up and the rpm kept dropping to zero. So I was wrong about the cold start. It is a hot start that is giving me problems. And could someone point out to me where the BAC would be located? Thanks.

satch

iTrader: (1)

On a S4 turbo it's located on the passenger side and towards the top of the throttle body. It has a small metal tube which has an idle adjustment screw in it. Since your car seems to idle fine for a period of time and only becomes problematic after driving for a while makes one suspect your problem lies elsewhere but check the solenoid anyway.


https://www.rx7club.com/showthread.p...light=bac+pics

J5sense

iTrader: (3)

OK first thing is first.

1) warm up the car, should be 1/4 on the temp gauge on a s4. make sure the thermostat is open by touching the upper and lower radiator hoses. they both should be hot.

2) shut off car remove the intercooler and adjust the TPS sensor. I use a volt meter. set it to resistance and measure and adjust the tps screw till you get the tps reading to about 1050 ohms. do a search on this. when you have you volt meter hooked up you can also open the throttle all the way and make sure the sensor is reading 4000 + ohms

3) install intercooler, by the front coil pack there is a set coupler connector. a green 2 wire connector. conect a wire from one pin to the other. then start the car.

4) with all the electrical stuff off and the engine still warm adjust the BAC valve screw till you get a 750 rpm. S4's had a variable resistor and since you have a rebuilt motor it should be adjusted.

5) to adjust the variable resistor (by the airbox has a lean rich screw) with the engine still runnning and the connector still jumped adjust it till you have the highest rpm. should be slightly left to the middle most point inbetween lean and rich. now adjust the bac valve to 750 rpm agan

6) set the ignition timing now with the car at 750 rpm and the connector jumped car warmed up. search on how to do this since i dont like writing a book.


if you have any problems getting to this point first off check for vacumme leaks. as i found block off plates for the acv leak if you dont use silicone sealent. the lower manifold to rotor housing gasket leaks too if sealent is not used with the gasket. with the car running take a can of brake cleaner and spradically sprak in bursts around the intake manifold and vac lines looking for changes in the idle. if you found a spot where the idle fumbles you have a leak. leaks also have a hissing noise.

another common problem is engine grounds. exsp the one under the rats nest. do a search on this as there are many nice pics.

another thing to check is the s tube from the airbox to turbo it cracks from heat and causes the airflow sensor to read wrong.

when you start a s4 cold it sould idle to about 1700 rpm and then fall to 750 when warmed up this can take 3-10 min depending on temps. there are 2 adjustments to adjust this

good luck

JermsBoo

Thanks. I also found the repair manual in the car so I'll be using that too.