Rough Idle in GenIII

Demons1964 · #1 10-05-2006, 10:30 AM

Driving home last night stuck at the lights and the idle suddenly became really rough (like being buffeted in high winds). The revs aren't dropping but the idle is erratic and it feels like it wants to stall. Much more amplified in drive/reverse but I can still feel it in neutral. There's a slight lag when increasing the revs but once it's up high it seems ok. No fault codes logged. It's almost like it's missing on 1 cylinder but only at idle. My thoughts are: faulty lead, faulty IAC (or whatever the equivalent is in the GenIII), leaky vacuum hose in the inlet manifold or even crap stuck in the throttle body. Any other thoughts from those more learned? Also can anyone give me a how-to on how to remove the throttle body and clean it?

Doctor Bob · #2 10-05-2006, 08:32 PM

if its not a misfire i would be guessing the PCV hose is leaking vacuum at the throttlebody end, it may not log codes for a few km of driving.

Rob

Demons1964 · #3 11-05-2006, 09:04 AM

Thanks Rob, I'll have a look at it on the weekend. I've done about 30km with the problem and no check engine light yet. I'm hoping it's a vacuum hose because I started it cold last night and it ran fine, but once the engine bay temp got up after a couple of minutes the problem started again. Makes me think the hose is expanding with the heat, thereby opening up the leak and explains the symptoms. Thanks again for your help.

PSK · #4 13-05-2006, 06:47 PM

Removiong the throttle body is simple on the ls1. Just 3 bolts. There is also a coolant hose running through it. Once you take that off just connect it to the block directly bypassing the throttle body. It's just meant to warm up the throttle body in colder climates where it snows. eg USA
When cleaning be careful not to get any carb cleaner in the sensors. Pull off the IAC and give it a good clean too while your at it. It's definately worth doing although it may not solve your issue. Vacuum leak sounds on the money to me.