Okay,

I was able to get a 1990 RX-7 started that had been sitting for 2 years after the car stranded the owner and no one has been able to get it started since.

I replaced the ECU, CAS, Plugs, and battery. Thing fired right up and then I set the timing after the idle came down to around 750 rpm. I know with absolute certainty that the car had been and was at the time , running very rich. Not only did the exceptionally fouled old spark plugs that I pulled tell me that, but the smell of the exhaust at idle told me as well. I have a brand new water thermo sensor on the ready to replace the old should the old one return out of spec resistance values. But for the sake of the argument, let's say the thermo sensor is good, and now the question becomes, what other sensors or devices could cause the engine to run rich? BAC? TPS? bad MAF (my engine has a MAF correct)? If any of these three were bad, wouldn't they manifest so with a bouncy eratic idle? Because I can tell you the idle on this thing is almost dead on spec at 750-800 when the engine is warm.

I greatly appreciate your help in advance.

 

Bad connector/wiring between ECU and water thermo sensor.
Bad O2 sensor.
Bad connector/wiring between ECU and O2 sensor.
AFM
Wiring to AFM
Intake air temp sensor
Wiring to intake air temp sensor
TPS/wiring to TPS/TPS out of adjustment.
Dirty/leaking/clogged/inoperative fuel injector(s).
Misadjustment of idle fuel mixture (this will affect open loop operations only, i.e. idle, acceleration, deceleration); cruise the ECU will adjust to stoiciometric if the ECU and O2 sensor are playing together properly.

Recommend you pull codes (easy in an S5, you can get it to flash MIL light, don't need a code checker)

Also check for closed loop operation at cruise, i.e. rich/lean flag on CPU should toggle about 8x in 10 sec at cruise (not idle) rpm. See AFM.

Another thing you can do, esp if there are no codes, is pull up the carpet on the right side, get to the ECU and its connectors, and backprobe each pin of the ECU and compare against the numbers in ch 4 of the FSM. There are values published for each pin in both the ignition on, not running condition and the running at idle, engine warmed up condition. If there is a bad sensor or wiring, it should show up as a voltage out of range.

 

INCREDIBLY HELPFUL response. Thank you very much Calpatriot. I'll let you know what I find today and post back with the results next week.

How often to O2 sensors fail without setting off the CEL?

 

A very intersting question. I do not know about your S5, but in my S4 the car ran quite well for a long time, and I (silly me) did not check the codes because it seemed to have no problems. In fact, it was running in a default rich mode, which is what it does when it sees no O2 sensor. I suspect it was throwing an O2 sensor code the whole time, but i did not know it (the S4 has no CEL).

Then, one day, it started running terribly. To make a long story short, I eventually found that it was intermittently detecting and failing to detect the open in the wire to the sensor. When it thought no sensor was present, it drove well. When it thought there was a sensor present, it drove terribly, but threw no code. It seemed to me that it 'found' the non-existent sensor on about half of the starts.

 

whats CEL?
i never heard that.

 

It's the acronym for "check engine light."

 

im retarded

 

RX-7 run rich when idling. They run in the low 13 afr. The 13afr is rich. The 02 has nothing to do with the mixture at idle.

 

that is good to know. The other thing it does, on the way to operating temperature and about 2 minutes after starting up when cold, is bounce around on the idle, hungting from 1100 RPM to 1500 RPM. I will be checking for vacuum leaks today with starter fluid and will removing the BAC to clean the carbon out and test the values. Anything else I should look at?

The car is not giving me any check engine codes presently.

 

Check operation of the fast idle cam & thermowax.
Check operation of the double throttle diaphram with a mityvac. The diaphram deteriorates, perforates, and provides a vacuum leak source *only* when the thermovalve (back side of throttle body, right side) is open (cold temp). Once warmed up, the thermovalve is closed and (if operation correctly) isolates the intake from the double throttle diaprham.