DesertSkies

I am new to this forum, so forgive me in advance if I violate any rules of etiquette. I did use the "Search" function but did not find a specific answer to my question.

I have a 1991 RX-7 Convertible. I just had the A/C system replaced ($$$$). But now when I engage the clutch at a traffic light, or even if I decelerate below about 10 mph, the engine dies. It is obviously the load created by the A/C compressor on the engine, and for some reason the idle speed is not compensating when the A/C is on.

Any suggestions for "most likely" cause? My own first thought is some malfunction in the BAC Valve, or one of the sensors ... or even a malfunctioning ECU. But replacing any of those bits is not an option, since parts seem to be totally unavailable.

Just so you know, the engine idles rock solid and beautifully when the A/C is switched off. The problem occurs only when the A/C is on.

Any thoughts or personal experiences with this problem would be appreciated. If the problem cannot be fixed, the car will have to go. Going without A/C is just not an option in the SoCal desert, where temps are over 100 every day from May to October.

RicerJ

switch it off when you slow down and then turn it back on lol

j9fd3s

off the top i cant recall how they kick up the idle in the s5...



my first thought is to check the idle speed, the FSM (shop manual) has a really easy check, and then the TPS, again its simple



i didnt look at my s5 intake, but the s4 uses the BAC valve to increase idle speed when the a/c is on, so checking the BAC would be a good idea.



it might also be something odd like the clutch switch, but thats kinda left field, start with the basics

DesertSkies

Thanks for the thoughful reply, j9fd3s. The idle speed is fine, so that does not seem to be the issue. And as I said, the engine will actually die the instant the clutch is engaged if the vehicle is moving less than 10 mph. So the clutch switch may be part of the problem (ECU not getting a signal that the clutch is engaged and therefore the ECU is not responding with a signal to the BAC to open) ... though I would think a non-functional clutch switch would also interfere with engine start-up.

The throttle postition sensor (TPS) may also be involved. That is a good suggestion, and I will check it.

Thanks again. I appreciate your help.

j9fd3s

i'd check the idle speed anyways, as the ecu will kinda compensate if its off, but maybe not always. takes literally 1 minute.



there are actually TWO clutch switches, one for the ecu, and one for the americans (its not used in any other market), so the ecu switch can be bad, but the car will start fine, or vice versa



i'm working on one if these today, so i'll see if i missed anything

j9fd3s

nope! ecu controls the idle speed, thru the BAC only. so all of the ecu INPUTS need to be right, otherwise its going to do strange things

DesertSkies

Apologies, j9fd3s, but your last post confuses me. What was the "Nope!" referring to?



I'm still checking the various ECU inputs, so maybe one of them is faulty and causing the problem through interruption of the information pathway pre-ECU.



I did check the idle speed, as you suggested, and while it was a bit low at 500 RPM, increasing it to 850 did not solve the problem. The engine still dies at low speed when the A/C is on.



So I'm off to buy a multi-meter so I can check the Throttle Position Sensor...... that's next on the checklist.

j9fd3s

nope there are no other valves... the turbo and 1st gen cars have an extra valve to move the idle up when the ac is on