Idle Drop/Stall with A/C on????

[Canyon Racer]

Okay, I've combed the forums and the TSRM. Which of you Supra techies can tell me what's wrong...when I turn on the a/c, the idle doesn't go up. It drops to around 500, and sometimes almost stalls. Sensor? Wire? Relay? Where do I look? Thanks!

86.5 MKIII, 7M-GE, 5-Speed

 

[CRE]

Code 51?

http://www.cygnusx1.net/Supra/TechTips/engine_error_codes.aspx

 

[Canyon Racer]

Code 51?

http://www.cygnusx1.net/Supra/TechTips/engine_error_codes.aspx

Yes, there's a Code 51 stored in the Super Monitor diagnostics. Code 51 in the TSRM paints a very broad brush as to what it could be though. Was hoping there was a common cause of no idle-up when a/c is turned on.

 

[amichie]

Have you cleaned out the ISCV? It may just be blocked and can't let more air in for idle up. Does it idle up when you turn the steering wheel at idle?

 

[CRE]

It's much more likely that the ECU isn't getting a signal when the A/C is on... and as such isn't idling up.

Check the wiring that runs to the compressor. Then look at the third to the last tech tip here: http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=58 for info on how to test when/if the TCCS is getting a signal when the A/C is on or off.

Always post any codes you find whether you think they're vague or not.... saves more time than you might imagine.

 

[jetjock]

If you're seeing 51 with the AC off it means idle speed control is disabled. Pretty tough for it to control idle for any reason when it's turned off...

 

[CRE]

Thanks JJ.

He's got a 5 speed so check the A/C's wiring and the IDL switch in the TPS: http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=101

Anything else missing?

 

[jetjock]

Do it the easy way first:

1) No 51 with the AC off and throttle closed.

2) 51 with the AC off and throttle cracked.

3) 51 with the AC on and throttle closed.

Anything else, do what you suggested. Clutch activation without idle up is usually caused by a bad AC amplifier. Course there could be a wiring problem in that area too.

Fwiw AC idle up is not as simple as other idle ups in that for AC the ECU advances timing in order to "get a jump" on idle speed. It's why turning the AC on causes an immediate increase in idle, before it drops. If it was just a matter of manipulating the ISCV it would drop first the way it does with headlights and defog operation. Bet ya didn't know that did ya?

 

[Canyon Racer]

Wow...thanks for all of the tips! I'll take them step by step tomorrow until I find the problem. If I nail it, I'll post the result.