Wierd idle w/ AC at max

1989 T-Type 3800 VinC, 46k miles

I was playing with my climate controls today after I recharged my R134A refrigerant and noticed that when my AC is on max, my idle fluctates about 300RPMs. It just goes up and comes right down. I was curious, so I checked my SES light for codes. I got code 26,39, and 41. I'm not concerned about the 41 (hit an alligator on my way home when I first got the Olds that the engine was originally in) but the other codes are new. I referred to my chiltons and this is what i found:

26: QDM "A" circuit
39: TCC problem

I searched the forums for an elaboration and came up with this:

26: Quad Driver Module fault, not to immediately replace the PCM if the QDM is failing because more than likely it is a device that the QDM is controlling that is at fault (http://www.automotiveforums.com/vbulletin/showthread.php?t=263912&highlight=code+26)

39: Torque converter clutch( Check ECM connections, check for faulty Torque converter clutch solenoid), coil pack with intermittent open (http://www.automotiveforums.com/vbulletin/showthread.php?t=441568&highlight=code+39)

According to the codes my problems lay either with my freshly installed tranny from a junkyard (with my TC from the 45k mile tranny), my recently "upgraded" coil packs taken from the local pick and pull junkyard (I did this: http://www.thejmfc.com/autos/delcoignition.html), or my freshly installed ECM, also from a salvage vehicle.

I'm going to try to swap out ECM's (I'm going to install the ecm that originally went w/ this engine that was put into my PA when its ECM went south) and I'll post back. In the mean time, I would appreciate it if anyone had any more ideas as to the source of my problems.

Ok, I just replaced the ECM but the problem is stll there. I forgot to mention something earlier though. Whenever the RPMs idle back down I hear a click in the engine bay towards the front passenger side before it idles up again and then down, click, up again, down, click, up again.

Any thoughts?

Ok, I just replaced the ECM but the problem is stll there. I forgot to mention something earlier though. Whenever the RPMs idle back down I hear a click in the engine bay towards the front passenger side before it idles up again and then down, click, up again, down, click, up again.

Any thoughts?

Since you have a code 26 and 39, I would take a look into the TCC circuit since it is one of the components driven by the QUAD driver. Here is a link which may help you out...The article of interest is Case Study 2 about half-way down the page.

http://www.asashop.org/autoinc/april99/techtotech.htm

That article referred to a TCC solenoid... Where and what is that on a transmisison? If I need to, I can go to the shop where I had my tranny swapped and pull anything else that I need...assuming the mechanic hasn't hauled the old tranny off to the junkyard yet.

That article referred to a TCC solenoid... Where and what is that on a transmisison? If I need to, I can go to the shop where I had my tranny swapped and pull anything else that I need...assuming the mechanic hasn't hauled the old tranny off to the junkyard yet.

First, I'm only saying that this is a possible cause for your problem. I would check its operation before dropping the pan. If it were me, I would put a labscope with a current probe on the TCC circuit and check the solenoid for proper operation when it is energized. The transmission pan has to be dropped to gain access to the solenoid which is located on the valve body.

Ok, I just replaced the ECM but the problem is stll there. I forgot to mention something earlier though. Whenever the RPMs idle back down I hear a click in the engine bay towards the front passenger side before it idles up again and then down, click, up again, down, click, up again.

Any thoughts?

Let’s go back to your idle problem for a minute. I assume that the engine is in park or neutral when the rpm fluctuates that much. Now, focus on the AC compressor clutch and see if it engages in harmony with the clicking noise. If it does, the idle should increase immediately after the clutch engages. Remain focused on the AC clutch, until you here the click again and at that time the clutch should disengage and idle return to a lower rpm. This “clicking and rpm fluctuation” is normal operation for AC compressor cycling. You should not notice the rpm fluctuation as much while the car is in gear, either reverse or forward gears. If the compressor is cycling too often, you have either an overcharge or undercharge of Freon. Have you checked your high & low side line pressures?

The quad driver & TCC codes are not related to the above, however you need to follow stuzmans advice and identify the source of that issue also. Since you recently replaced the transmission, be sure to check the connector & wiring going to the TCC terminal on the transmission. You can also watch TCC engage signal on a scanner while driving. If you have the engage signal and the circuit completes through the wiring and connector, then suspect a solenoid problem.:2cents:

If the compressor is cycling too often, you have either an overcharge or undercharge of Freon. Have you checked your high & low side line pressures?


That would do it. A friend of mine had a bout a half can of R134 left and we put it in my car (it has already been converted, but doesn't seem to blow cold anymore).

I did check and see if the RPM's fluctuated when in drive and they do, but it seems to fluctuate a tad bit slower than in park.

I'll try to fiddle with my transmission when I get in from work, probably tommorow since I'm busy the rest of today.

Thanks for the info so far :)