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LOW RPMs when AC is turn On

999 Views 2 Replies 2 Participants Last post by  zorro17
My 93 Cabriolet, has AC and after I got it repaired last week, I notticed that when I tuen on the fan on the AC settings, the RPMs stay at the same level, around 900rpm. before I got the AC fixed, the RPMs will rise up to 1200rpm. I asked the mechanic and he is playing dumb. Do you gusy know where can I check, or where can I increase the RPMs. Thank you
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Moved this to the general forum as it isn't a frequently answered question, nor a DIY guide.

What did you have repaired?

The reason I say this is two fold. The normal way to time a Digifant is:
loosen the diz clamp bolt.
Start the car and allow it to come up to temp and cycle the fan one time.
Then disconnect the CTS sensor and rev the car above 3000 3 times.
Then while holding the RPM at 2250, you should set the time at 6tdc with a timing light.

There is another way that only involves statically setting the timing manually by aligning all the timing marks to 6tdc.
Then loosen the Diz clamp bolt
Take the plug off the DIZ and remove the rubber boot, These break really easily and can cause grief which is why you remove it from the diz to uncover the boot.
Reconnect the plug to the diz.
Using the red lead of your DVOM on the green/white wire in the plug of the dis you place the other black probe on ground
You move the Diz if it isn't at 11V. if it isn't at 11V but 0, then move the diz clockwise so the DVOM reads 11V. Clamp it your done, you don't need 2 people to time it.

Getting this is critical for the digi to keep time.

Digifant will maintain idle and there isn't a true idle adjust on the engine persay.

It uses the A/C relay to enable a signal in the digifant controller to increase the voltage to the ISV valve that is round and attached to the
front of the throttlebody.

I have 2 of these and one is a bugger, the other will increase the rpm when the a/c is engaged.

DO NOT UNPLUG the ISV when the key is on you can fry it or the ECU.

The turning of the a/c on enables the a/c relay to send a signal to the ECU telling it that the A/C is running the ECU then increases the idle by using the ISV Idle Stabilization Valve to increase the RPM of the engine to maintain it @1000.

Digifant by nature will monitor the engine via the knock sensor and hall generator and the Idle or time of the engine will fluctuate...
On my one car I just boosted the timing a wee bit and it does alright.

Vacuum leaks will kill the idle boost as well.
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Hi Brianno,

I had the AC repaired and althught the AC works and cools down, the problme is the low RPMs. before getting the AC repaired, the RPs will go up when I turned up the fan even whenthe compressor did not kick in. I am going to take it back to the mecanich but when i spoke to him on the hone he claimed he didnt know what i was talking about. there was another thread that recomended unpliugging TD1, so I found it and unplug it and plug it but nothing happend. I will check the fuse box to see if there is something missing. I will try your suggestions to see what can I get. Thank you
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