Truck shudders at idle with A/C on

[Laser145]

Hey guys

Just picked up a new 87 R10 (305, 700R4, stock exhaust, emissions, etc).

It runs great, no codes from the computer... However... When the A/C is on and you're sitting at a stop light the truck will shudder every 15 seconds or so... feels like it's going to die, but never does... just shivers for a few seconds then the idle picks back up.

Also, When I operate the power windows, the battery needle drops... you can tell it's a strain. Is that normal?

Cheers
Taylor

[Smoothride]

what temp is the AC at, it might be cold. blanket?

[old Rusty C10]

that is the cycling of the compressor.. its pretty normal also try lubing the tracks on the power windows and see if that helps alot of time it lags because of friction

[Laser145]

What kind of lube would you use for this... I have new seals, so this makes sense.

Originally Posted by old Rusty C10

that is the cycling of the compressor.. its pretty normal also try lubing the tracks on the power windows and see if that helps alot of time it lags because of friction

[88Jimmy4x4]

isnt there an idle stop solenoid that pushes throttle to rev up some once compressor kicks on?

[Laser145]

Would this solenoid also be responsible for increasing the idle at cold startups?

Originally Posted by 88Jimmy4x4

isnt there an idle stop solenoid that pushes throttle to rev up some once compressor kicks on?

[86dragracer]

1987 should be fuel injected right? If so I would look more toward a faulty idle air control valve. Listen for the compressor to cycle and see if the idle drops at the same time. The IAC valve might be sticking and not able to catch the extra load placed on the engine.

[88Jimmy4x4]

Originally Posted by Laser145

Would this solenoid also be responsible for increasing the idle at cold startups?

no that would be the choke, this solenoid gets its signal from when the compressor is on it idles up the throttle to compensate...you can visually see if its working or not

[Firebirdjones]

Originally Posted by 88Jimmy4x4

no that would be the choke, this solenoid gets its signal from when the compressor is on it idles up the throttle to compensate...you can visually see if its working or not

In most cases,,,those solenoids aren't there for compressor operation. If it doesn't physically have a wire running to the compressor power wire to trigger the solenoid,,,then you are simply looking at a TCC solenoid.

They have been used since 71 as an emissions device (transmission control spark) and they are designed to kick on when the trans shifts to 3rd gear (or 4th gear with a manual) and kicks the throttle arm up a tad so when you let off the gas,,,it doesn't close completely, less engine braking, less throttle movement, less gas used.
The second operation that this controls (up until computers took over) are the vacuum lines running through it and to the vacuum advance on the distributor (hence the name transmission,,,then control spark) The transmission gear activates this solenoid,,,not only kicking up the carb throttle,,,but also now allowing vacuum to travel to the advance can on the distributor,,,,giving you additional timing during high gear cruise operation only. Once the tranmssion is downshifted from high gear,,,,this solenoid cuts off vacuum supply to the distributor,,,and releases the throttle arm so the engine returns to idle. This reduced timing is why so many cars got crappy gas mileage around town,,,but less timing reduced emissions and that was the whole purpose of it

I should also add that in some instances these were used as "anti-diesel" solenoids in which case they were activated when the key is turned on and off. In this case your engine idle speed is adjusted using this solenoid only,,,not the screw on the carb. That way when you turn the key off the throttle blades close completely,,,stopping the diesel or "run on" that is sometimes an issue.