Hey guys i have a major problem everytime my car is fully warmed up. When i start it it runs rough bounces up and down and even stalls sometimes. I usually have to give it gas for like 1 minute until it becomes stable. I was thinking it was the BAC so i cleaned it and everything the coolant line on it looked corroded but it should still work. Checked the TPS works fine. It has to be either BAC Valve or The Air flow meter. what do you guys think? - 88 rx7 s4 turbo 2 ALL STOCK

 

could be you need to adjust your Throttle Position Sensor.(TPS).
another "guess" is Dirty injectors,a bad water thermo sender(back of waterpump),or a slight vacuum leak.(Sometimes you can get a slight Vacuum leak when cold,until the car warms up and will then make a hose Pliable and seal up...Sometimes.not often.)
But I would check the TPS first..there are many threads on How to adjust the TPS on forum.

 

He said when fully warmed up.

I have a similar issue. Anytime my car is warm (as in, any indication shown on the temp meter besides the bottom) my car is hard to start. Not really hard, but I have to turn the key to start, then let go. Then I wait for the fuel pump relay to kick off and I try to start again and it fires right up. I don't even have to crank it when I try to start it the first time. I can just flick it into start briefly turning the starter for less than a second then do it again after the pump kicks off and boom, it fires up.

Strange problem. I know how to circumvent the issue easily, so I have not asked yet until now. I have however searched for a solution for about 6 months now to no avail.

 

The tps works fine im pretty sure the fuel injectors are running good cuz it runs rich a little bit. A lil back fire. But im considering deleting the BAC valve do you guys think this will give me any benefits on my start ups?

 

get rid of the BAC and kiss your idle good bye, at least I am told that is what keeps the car from stalling...

did you do the basic tune up first, wires plugs, oil change...

it doesn't have to be the bac or the AFM, I would adjust the idle, adjust the TPS all that stuff too, Old electronic components can just go stupid sometimes...

and also if the car is 100% stock it should NOT backfire something else is wrong somewhere...

 

I don't think that will help, and it may cause new problems. The BAC valve does not change the mixture, so it is not likely the source of the backfiring/poor idle problems.

But, you can check the BAC valve very easily, per the FSM procedure. With the car idling, pull the electrical connector off of the BAC valve. The idle should decrease slightly. If it does, the BAC valve is working. if it doesn't it is not. If your problem is still there with the BAC valve connector off, removing the BAC valve won't help either.

1. Any trouble codes?
2. O2 sensor voltage at idle greater than 0.45v?
3. Timing
4. Advance
5. Idle speed adjust
6. Idle mixture adjust
7. Check (no dropouts) and set tps to exactly 1 k ohm
8. Stethescope injectors for nomal (clicking) operating sounds
9. Good spark present on all 4 leads, especially the leading 2?
10. EGR valve check per FSM? (should run worse with it disconnected)

 

the bac valve connector when disconnected doesnt affect the car idle i was thinking maybe the bac valve connector is messed up or something ill try to fix that and see if that solves the problem.

 

The BAC valve generally only operates to keep the car idling around stock (750), if the car idles there just fine without the need for the valve to be open, then disconnecting it won't have any effect. What you should do is turn ALL load on (A/C, efan if so equipped, radio, headlights, everything) and then disconnect it. Generally if your car's idling ~800 on it's own without the BAC, turning all of that on will drag it down a bit and the BAC will kick in to compensate.

It sounds like your normal every day hot-start to me which is usually the following (in this order)

Compression
Injectors
Vacuum leaks
Coolant/Intake Air sensors

 

The only thing BAC related not already mentioned above, is that if the key is HELD to Start, the BAC will remain fixed wide open until the key is released to ON, then it'll go into its duty cycle.

Going wide open with key Held to Start helps starting to some degree.

 

Well i checked the bac valve and its working. Now im thinking that its the timing because. I get backfires when i rev to like 3000 rpm on a cold start and WOT on operating temperatures. Do you guys think this is a timing problem. Also my o2 sensor just went out im not sure if that would affect it but ima replace that soon.

 

Yes. (Been there, done that).

Without a properly operating O2 sensor the ECU stays in open loop mode, and runs the mixture at an arbitrarily safe (i.e. rich) setting. That's what it's supposed to do during warm up, but once at temp it's supposed to go into closed loop.

You are running a rich mixture all of the time, which tends to foul your plugs, cause poor idling, backfiring, missing, etc.

On my car I found that it sometimes incorrectly deemed the (failed/not connected) O2 sensor to be ok, and tried to use it to adjust mixture, and that was when the car ran the worst--almost disabled.

You are chasing your tail by trying to correct the problem somewhere else when the O2 sensor is bad. Get a new sensor (Autozone, $18, Kragen/O'Reilly, $20), put it in, reset the ECU, and start over.

Once in, it may take a few high power runs to clean up the spark plugs, or you can pull them and clean them.

I found that within a couple of drives my car was running great (the leaner mixture seemed to clear the plugs).

Once you have the O2 sensor operating, pull codes and check for closed loop operation. If there are no codes, and the ECU is going into closed loop, then you can worry about other standard tune up items such as timing, advance, idle speed and mixture.

If you replace the sensor and it still won't go into closed loop, there is another problem, and the rich mixture you are running will eventually cause the new sensor to load up and fail as well.

 

My 1987 turbo does something just like this. I can go out and start it right up, i can also can also set my turbo timer and let it sit and run for a half an hour. shut it off it will start right back up. BUT???? If i drive it 5 or 10 miles, i guess putting a nomal load on the engine. and then shut it off . When i go to start it back up it will roll over then stall then you can crank till ya burn a starter up it wont start.But if i turn the key on and off about 5 times it will start back up idling real ruff then it clears out and runs great again.IDK i need help as well and its none of the above. Wish Ice was still around , BUT IM GUESSING IT IS EITHER THE FUEL PRESSURE REGULATOR. OR A CLOGGED CHARLCOAL CANISTER. I HAVNT HAD A CHANCE TO GET TO IT LATELY, BUT I PULLED MY FUEL LINE AFTER TRYING TO START IT AND FUEL SPRAYED EVERYWHERE SO I KNOW THE PUMP IS WORKING, BUT IF THE RETURN IS CLOGGING OR THE PRESSURE REG IS STUCK CLOSED IT COULD BE JUST BUILDING PRESSURE IN THE LINE TILL IT PUSHES PAST , DOES ANYONE REALLY KNOW FOR REAL. I HAVE A KIIL SWITCH NEW 650 CC INJECTS , RTECK EMS/ECM NEW PLUGS HIGH END FUEL BOSH FUEL PUMP, NEW DAMPER BAC IS FINE NO VAC LEAKS, NO COIL OR COMPRESSION PROBLEMS AFM FINE TPS FINE CRANK ANGLE TIMMING FINE TURBO FINE OIL FINE. ETC ((((((((((((((((((WHATS NEXT GUYS)))))))))))))) ANYONE ............

 

THIS. Before you go chasing ghosts, why not trouble shoot using good information that someone has given you?

P.S.... It's NOT your BAC.

EDIT: Holy thread resurrection! Haha, didn't notice the last post before you was three years ago. Still, check your water thermosensor on the back of your water pump. That was the source of hot start problems (flooding and just super rich start when warm.) on two of my old 7's.

 

Ok thanks i dont think i checked that yet, you dont think it could be a pressure regulator stuck or a return line failing.???? im just trying to get a couple things ta check in stead of bouncin off the walls . it just started doin this one day. it blows my mind. Thanks.

 

I don't know, really. The "turning the key on and off 5 times" thing you mentioned is interesting though.

I'd check the list above first concerning hot starts (compression, injectors, vac leaks and temp sensors), then check voltage to the fuel pump (Engine off, key to on) after driving it around a bit to induce the problem you are having.

Better yet, drive around and shut the car off, confirm your problem has been induced, then jump the fuel pump check connector and try to start it.

 

Ok injectors are clickin , fuel pump a buzzin no worn hoses or intake leaks had that happen before. Compression is a bouncin at 105 to 120. I think that's in spec not sure. Egine rebuild only has like 4500 mile on it. Don't drive her much since I blew it up at the track . Spark plugs are ok and it starts fine when cold. The temp sensor I'm not sure. WHAT IS THE VOLTAGE OF THAT THING WORKIN. ITS SSHOWIN 1.2volts. Idk iwill inform when I have found this weird problem

 

The Water Thermosensor should be 2 to 3 volts cold and about .5 volts fully warmed.

And your Pressure Regulator Control Valve, which supplies vacuum to the FPR at certain times, should not have vacuum when starting a warm turbo engine for about 50 seconds and then the vacuum returns. The absence of vacuum increases the fuel pressure by the FPR.

 

the '88s came with SD10A/9A plugs, you are not still running them are you? autolite also copied those crappy plugs, if so throw them away and run the appropriate BUR7EQ/9EQ plugs.

 

Thanks and yea I run ngk never ran autolite. Thanks I'm a check the fpr for vac

 

the SDxxA plugs were factory NGK.

 

My 87 tii is having the exact same problem.