Engine shudders when A/C kicks on

[contraption22]

My TBI Acclaim has an issue that when the A/C kicks on, the car will shudder and everything loose in the car will shake.. including the steering column. It will shudder, then gradually stop. Then once the compressor cycles, it will start all over again.

This went away for a while when i had an underdrive pulley on it, but i had to put the stock pulley back because the alternator wasnt charging enough with the UDP on.

It only does this when it's in gear (auto).

Any help would be great. Thanks!

[black86glhs]

Mike, does the idle drop real bad when it kicks on? If not look at the motor mounts and see if any are bad. Clean the IAC and the passage. Could be the IAC is slow to respond when the a/c kicks on.
Could also be a problem with the a/c compressor.

[JDAWG]

I would start checking voltages, could need a new battery, alt, wires, etc

[contraption22]

I will have to look into cleaning the IAC. Dunno why I didn't think of that myself. The motor mounts are new. The compressor is in good shape. Alternator is charging well.

Thanks all!

[contraption22]

Well it idles at about 900-950 rpm in neutral/park. Put it in drive and it drops some. Put it in drive with the compressor engaged and it drops down to 650 or even less.
I unplugged the IAC and it got worse. So im thinking it's still working, just maybe dirty. I don't think I can get the IAC out without removing the throttle body, so it's going to have to wait for another day when I have gaskets ready.

Thanks all for your help!

[JDAWG]

check volts when it engages, mine used to be pretty bad, a better battery and i cant even feel it now, not really the reason i changed the battery but whatever

[contraption22]

I have no doubt the voltage will drop a little. Its losing 30% of it's rpms! lol And there is shudder when any other electrical accessory is turned on. Lights, rear defogger, cooling fan. Just the compressor. I think it's just the load from it and the IAC cannot keep up.

[black86glhs]

I have no doubt the voltage will drop a little. Its losing 30% of it's rpms! lol And there is shudder when any other electrical accessory is turned on. Lights, rear defogger, cooling fan. Just the compressor. I think it's just the load from it and the IAC cannot keep up.

Do the RPMs come up slowly and the vibes start to go away? It sounds like a slow reacting IAC along with the heavy draw on the alt like you guys mentioned.
Try cleaning all the ground connections.....well, clean all the main battery connections and the alt connections along with all the grounds. This may help it out and lower the voltage drop.
Plus it is cheap to do.

[contraption22]

Well i couldnt get the AIS motor off the throttle body, but I did unbolt the throttle body and spray some throttle body cleaner in there. It helped for a short time, but not the problem is back.

I was doing some fooling around with the Monitor 4000E. According to it the "desired idle speed." is 520 rpm. My guess is the computer is constantly trying to achieve this rpm for a steady idle. Is this correct?

WHy would it want the engine to idle so low?

[looneytuner]

I thought manual transmission idle was 950 and atx was about 1200?
As I recall the AIC is HARD to pull out. I pulled one and soaked it in Carb cleaner for a day and it still took a big yank to get it to free up all the way.

[135sohc]

I thought manual transmission idle was 950 and atx was about 1200?
As I recall the AIC is HARD to pull out. I pulled one and soaked it in Carb cleaner for a day and it still took a big yank to get it to free up all the way.

ATX should idle lower, manual higher

my 5 speed TBI idles between 900-1000 rpm.

[black86glhs]

Well i couldnt get the AIS motor off the throttle body, but I did unbolt the throttle body and spray some throttle body cleaner in there. It helped for a short time, but not the problem is back.

I was doing some fooling around with the Monitor 4000E. According to it the "desired idle speed." is 520 rpm. My guess is the computer is constantly trying to achieve this rpm for a steady idle. Is this correct?

WHy would it want the engine to idle so low?

520 is too low, IMO. Not sure what it should be factory. Mike, you might want to just tweak the minimum idle up to around 700 and go with that.
Do you think the balance shaft chain might be broken and the balance shafts arent counter-rotating. The A/C might magnify this problem. Just pulling that one out of thin air.

[contraption22]

Well i cannot get a definitive idle speed setting out of the FSM, only that it should be between 950 and 1050 with some kind of Miller tool with a .125" orrifice attached to the PCV line.

What I found on the 4000E was that there was a "desired idle speed", which read 520rpm. I have no idea what this means or what this is supposed to do, but all i can imagine is that the computer wants the engine to idle at 520 rpm. And if the idle is mechanically set to 900, it's certainly not going to open the AIS when it wants to drop to 650 with the air on.

The car run smooth as glass in all other conditions. But when the A/C is on, and the car is in drive at a stoplight... there is a horrible vibration that shakes the steering column.

I had a vacuum guage on it to see what happens and when it surges like this, vacuum drops from 15" to 10" and then back up.

[contraption22]

Well I played with all kinds of ignition timing settings. That didn't so anything. The only difference I can tell now is that it has gotten worse because of the new slightly stiffer motor mounts.

Some more details. It doesn't do it when i first start the car and the engine is cold. By the time I get to my 3rd or fourth stoplight on my way to work it happens.

The A/C compressor engages and the the vibration comes in waves, surging at about 5 seconds at a time. The first surge is light vibration, the next a little more, then heavy. Then the compressor will dissengage and it goes away until the compressor kicks on again.

It's getting really frustrating. I've gotten into the habbit of putting the car in neutral at stoplights.

[DodgeZ]

Well I played with all kinds of ignition timing settings. That didn't so anything. The only difference I can tell now is that it has gotten worse because of the new slightly stiffer motor mounts.

Some more details. It doesn't do it when i first start the car and the engine is cold. By the time I get to my 3rd or fourth stoplight on my way to work it happens.

The A/C compressor engages and the the vibration comes in waves, surging at about 5 seconds at a time. The first surge is light vibration, the next a little more, then heavy. Then the compressor will dissengage and it goes away until the compressor kicks on again.

It's getting really frustrating. I've gotten into the habbit of putting the car in neutral at stoplights.

I am guessing since it is a TBI it doesn't have a custom cal? I know from messing with my AEM stand alone the A/C stuff is tricky, aka how much "load" to add when the A/C is on. Running the a/c at the same RPM needs more fuel. I'd guess that a bad o2 could cause a problem if it is running right on lean and then the A/C kicks more load on. Kind of a long shot but what the heck...

[contraption22]

I am guessing since it is a TBI it doesn't have a custom cal? I know from messing with my AEM stand alone the A/C stuff is tricky, aka how much "load" to add when the A/C is on. Running the a/c at the same RPM needs more fuel. I'd guess that a bad o2 could cause a problem if it is running right on lean and then the A/C kicks more load on. Kind of a long shot but what the heck...

Hmmm, Interesting thought.
I wonder if the cycling could be related to the cycling between rich and lean.
I have a fresh 02 for it. I'll pop it in for the helluvit.


Thanks!

[contraption22]

Changed the 02 sensor. Didn't help. Needed it anyway tho. also checked cam timing. Looks good.
I might try changing out the alternator next.

[DodgeZ]

Changed the 02 sensor. Didn't help. Needed it anyway tho. also checked cam timing. Looks good.
I might try changing out the alternator next.

sorry dude

[contraption22]

sorry dude

Hey man, no problem. I appreciate the idea and taking the time to post. It motivated me to change out the 02 sensor anyway, which i had intended to do months ago.

[Turbodave]

How are the A/C system pressures? Could have an issue with the A/C system that results in higher than normal pressures/and increased load.