[Brooksy]

I recently bought a 91 sierra and rebuilt the engine, so I haven't driven it much yet, just finished putting it all back together. I started up the A/C today and the revs went up to 2000 rpm, from the standard 850rpm, has anyone got any clue why? I understand that the rpm should increase, but I wouldn't have thought it would rise 1000+rpm?

[MacDaddy]

Brooksy wrote:

I recently bought a 91 sierra and rebuilt the engine, so I haven't driven it much yet, just finished putting it all back together. I started up the A/C today and the revs went up to 2000 rpm, from the standard 850rpm, has anyone got any clue why? I understand that the rpm should increase, but I wouldn't have thought it would rise 1000+rpm?

That is all normal, nothing to worry about, its so the a/c has enough rpm's to actually do something, and so it doesnt stall out the engine when it activates, its called Idle Up, 2000rpm is normal...

[Brooksy]

Ah, I see! I've seen the idle up on a cruiser before, but you had to press a button to activate it. Does the idle up stop when the A/C reaches setpoint? I didn't run it long enough to find out, thought I'd check that it's nothing serious first!

[MacDaddy]

Brooksy wrote:

Ah, I see! I've seen the idle up on a cruiser before, but you had to press a button to activate it. Does the idle up stop when the A/C reaches setpoint? I didn't run it long enough to find out, thought I'd check that it's nothing serious first!

Yep... Once the thermostat reaches set temperature, yes the idle up will stop, and then kick back in again when the A/C activates again... all normal... if you have an electric thermo fan, that should start up, and cycle on and off with the idle up as well...

[johnmath]

The idle speed should be 1000 rpm +/- 50 with the A/C on and everything warmed up. You set the A/C idle with an adjustment screw on the A/C VSV. Here's the complete installation manual including idle adjustment instructions: http://www.suzukiinfo.com/sierra/samuraiacinstall.pdf

[Brooksy]

Thanks guys, that is exactly what I have been trying to find John haha lifesaver!

[Brooksy]

Went to try and find the idle up adjustment screw and I realised that it is actually the indoor fan that sets the idle up to 2k rpm, even with the A/C off and even when I switch the slider to heating.. Any ideas?

[Brooksy]

Scratch that, just found out that any electrical stress on the engine causes idle up, rookie error

[Brooksy]

I'm adjusting the idle up screw (or at least what I think is the idle up screw) and it seems to be doing absolutely nothing to change the rpm. I can see the actuator engaging. Is anyone able to take a photo of theirs for me please?

[johnmath]

There is also an idle up adjustment for electrical load, which is a bit pointless. Maybe it helps idle for a cold engine. There is an "idle up system" which is comprised solenoid on the front of the carby, right hand side of the carby when looking from the front. Whenever the fan, lights or rear defogger is turned on, the solenoid operates and opens the butterfly valve a small amount. There is an adjustment screw for the amount of opening. You can back it off so it doesn't do anything. See page 4-9 of the full service manual. http://www.suzukiinfo.com/sierra/suzuki ... 413fsm.pdf

[Brooksy]

Yeah I have tried that, the screw I have been adjusting is the one directly above the idle adjustment screw. There is no change regardless of which direction I turn the screw. There seems to be a switch or something that the idle up adjustment screw touches to change the rpm, but it does absolutely nothing.

[johnmath]

Get someone else to turn on and off the fan whilst you watch the carboy to see which bit is the actuator for the idle up. You should see it moving when it comes on or off.

[Brooksy]

I had my pop helping me, I could see the diaphragm engaging and pullin it in, but the idle up screw just does absolutely nothing, I took photos, but it won't let me post them

[Brooksy]

Bump, going back to work on this again this weekend, is anyone able to help me out here? A picture of your idle up would be greatly appreciated!

[johnmath]

Brooksy wrote:

Bump, going back to work on this again this weekend, is anyone able to help me out here? A picture of your idle up would be greatly appreciated!

Sorry, I ripped the carby out and put in a TB EFI from a Swift. (I could never get the carby idle sorted out LOL). The electrical load idle up isn't really needed. Just cut the wires to the actuator, or unplug it. There is a separate idle up system for the A/C, which is needed of course.

[Brooksy]

Hahaha classic! Where is the one for the a/c? I thought they would have been on the same screw?

[johnmath]

Brooksy wrote:

Hahaha classic! Where is the one for the a/c? I thought they would have been on the same screw?

I posted the link with the adjustment instructions and illustrations previously: http://www.suzukiinfo.com/sierra/samuraiacinstall.pdf

[Brooksy]

The samurai's are efi aren't they? The diagram I was looking at was different to my carby