ROCCO_16V

Hey guys, we were finally hit by a heat wave and even though I like to cycle my a/c every so often, I have been using it on a daily basis. Last summer I haven't used it as much because the center flap servo motor was stuck and no air was coming through, but it's fixed now.

Anyway, I got the car almost 2 yrs ago and the problem was always there, it did not really get any worse over time, this didn't really bother me until now, but I don't think it's normal... When I turn on the ac, the idle becomes very shaky - almost like losing a cylinder. The motor runs properly otherwise, no codes, fresh "R" coilpacks (1.8T), fresh tightened spark plugs, boost is there, etc.

The only known problem that I will adress soon because I got a replacement is a noisy P/S pump. It sounds like a muffled woodpecker cracking sound.

What would you check?

jjm's quattro

ISV - cleaning to start with. That sorted out my similar issue.

ROCCO_16V

That's a good idea that i haven't thought of (even though I've done it on my 16V Scirocco years ago).

Anyone else?

yodasfro

Could be a voltage issue. Or something to do with the compressor>serp belt tensioner>ps/pump.

ROCCO_16V

Hmmm, you mean the voltage drops too much and it makes the idle shaky, or something else? What's the lowest voltage that will still make the engine run properly?

The PS pump might be a problem like I said, but the tensioner was changed right before I got the car.

yodasfro

I would put a multi-metter on the battery and turn the a/c on and see how low the voltage drops anything less than 12v is probably not so good. So it could be p/s pump but I'd also take the serp belt off and see how freely the compressor pulley spins.

Jonny K

I have the same issue with my car - shakey idle with the AC on. In general, engine power seems significantly reduced with the AC on, so I leave it off usually.

ROCCO_16V

Update: I cleaned the ISV and it did help the problem, it improved the idle roughness but not completely which makes me think either:
1. I did not clean the ISV properly (which I doubt)
2. There is another reason why it's shaky and that combined with a very dirty (on the inside - looked like a coat of black soot) ISV made things worse.

Either way, it's an improvement and a fix that didn't cost me anything, so I'm happy.

yodasfro

I use wd-40 and a 9v battery with a spare connector to clean the isv. Q-tip and compressed air help too.

ROCCO_16V

Cool, I'll try that again because I had no "alligator clips" to connect it to a 12V source...