What causes the idle to pulsate when the AC is on? When the AC is off I have rock solid idle at 800. When the AC first comes on the idle bumps up just like it is supposed to 1150 - 1200. After a little while the idle starts to pulsate - high idle, low idle, high idle, low idle. What causes this? I can't stand it anymore.

 

It might be the BAC valve, it lets air in past the throttle plate when the A/C is on to keep the idle up, I eliminated it on my car and now I have to keep my foot on the gas when at stops with the A/C on or it'll kill the motor.

 

it lets air in past the throttle plate at idle (all the time, not just when the AC is on)

 

read this http://mrmazda.no-ip.com/gslseidle.html what you want to take notice in there is the BYPASS AIR SUPPLY the VENT SOLENOID VALVE and VACUUM SOLENOID VALVE which control the BAC (possible problems). read up on the proper procedure for testing and TPS and making sure it is set properly AND the STANDARD IDLE ADJUSTMENT PROCEDURE. from there you can check and test the BAC, clean if needed and see if your vent and vacuum solenoids are functioning properly.

 

Guys, I appreciate the input, but I think this has all been directed at a fuel injected 13B. I have a carbed 12A. Anyone have input on pulsating idle in a carbed car.

 

I don't think he has a GSL-SE. His profile/sig says GSL. On the GSL, there is a pot with a rod that pulls up to hold the throttle open a bit when the AC is on. Maybe there is a vac leak causing it not to hold properly, the diapham may be bad, or perhaps something is up with the solenoid that controls it (or the ECU that controls the solenoid).

I would download the Factory Service Manual and take a look at it. You will want to look at section 4A for the emissions stuff and section 50 if you need to trace wiring.

http://www.wankel.net/%7Ekrwright/ca...85_manual.html

 

Ha

 

Try adjusting the screw on the throttle opener a little, not sure which way, but it shouldn't take much. It's the black mushroom looking thing with a vac line going to it on the back of the carb.

 

Hrm, when I asked this, I was told that my Freon levels were too low and that is what was doing it.

I am going to fill it up at lunch, and I will let you know what it does.

 

Yes, I had this same exact pulsating idle on my '85 GSL. I saw I was low on refrigerant. Topped it off and idle is now stable.

 

Thanks guys. I'll top of the freon tonight and check the mechanism that raises the idle. I'll let you know how I make out.

 

When Dan asked his question, thats the first thing I thought ( the adjustment) then someone said low freon, and I realized or thought it wasn't pulsing that fast so he was correct, assuming it was the clutch kicking in and out.
So, if you look at the clutch (at the front of the AC comp), and that starts and stops spinning every few seconds or so,(affecting the idle) then you may be low on refrigerant.
AC on, the clutch should spin and cycle off every few minutes or so.
If the clutch stays engaged, and your idle rapidly goes up and down, then the throttle opener is out of adjustment, or you may have a vacuum leak, as gsl-se addict said.

 

*cries a bit*

We tried to add the freon at lunch today. The tap leaked bad and I only got 1/4 of a can in. Makes a small bit of difference, but nothing specatular.

I looked and the clutch is kicking on and off in my case. Take a look at yours.

 

I added freon this past weekend and I checked the AC clutch. The pressure at the compressor is low (~15 lbs) with AC on. But the idle is pulsating and the AC is cold. It has been hot the past few days in ATL and the AC is blowing cold. The clutch is staying engaged when the idle is pulsating. I did not see any obvious vacuum leaks.

I am suspicious of the little diaphram that controls the idle speed. I'm thinking it may have developed a leak cuasing it to loose the vacuum. I may not be able to fool with it again until next weekend.

Dantheman, want are finding?

 

I have been playing a bit with mine. Yesterday, the idle settled down a good bit. (temps went into the low 90's instead of this 100 degree crap) It bounced a small bit this morning, but not as bad. I am going to get some more freon sometime soon, and see how it works.

 

dantheman,

I tracked my problem down to the idle compesator being set too high. Apparently, I set the idle just a little higher than it should be. I backed it off a little bit and the idle got steady.

Did you get your idle problem resolved?

 

Cool there are more people with AC still on thier 7's just like me!! I know we are a dying breed because people want "weight reduction" but SON OF A BITCh it gets hot here in south texas during the summer. I cannot not sacrifice the cold goodness for hot sweaty *****. nope nope. Oh and sorry ido not have any useful info for this thread.

 

My vote is for the idle compensator adjustment also. I had the same symptoms, but my pressure was fine on the gauges. I jumped out the low press switch for troubleshooting purposes, and the idle still ran hi and then lo. That's when I say the idle compensator engaging and disengaging. Adjusted the screw on it until it stopped. Took off the jumper on pressure switch. By the way, I've been using a product called EnviroSafe as an R-12 substitute for many years. My AC works pretty good in hot Lower Alabama (LA).