High idle after removing intake and valley cover
11-04-2014, 09:56 AM
#1
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High idle after removing intake and valley cover Hey guys!
I've been chasing an oil leak for a little bit now (last part to check is rear main), and Sunday I decided to remove my intake manifold and the valley cover to see if the leak was coming from the top end. On install, I replaced the valley cover gasket, the front knock sensor (top plastic piece broke off) with a BWD, and the knock sensor harness (original and both connectors exploded on removal). I have an LS6 intake that's been ground down on the bottom with an LS1 valley cover and coolant crossover tubes. I made sure to put a dam of RTV around the knock sensors as well.
After getting it all back together and putting 100 miles on it, my idle RPM is at 1300 and I have a bank 2 (rear) knock sensor low voltage code with slight (soft) backfires when sitting at idle.
Everything was torqued to spec, knock sensors at 15 lbs, valley cover bolts at 18 lbs, intake done at 2 passes with final torque at 15 lbs. The only vacuum lines I had to mess with was the small one (HVAC?) going to the back of the intake, brake booster (disconnected from boosted not manifold), and of course the 2 PCV lines up front.
My question is, would a loose valley cover and/or intake manifold cause a big enough vacuum leak to warrant a 1,300 RPM idle, soft backfiring, AND set off a knock sensor? I cleared the code after it first appeared, then 5 miles later it came back. Car has a slight rock to it also at idle.
I'm going to tear it down again tonight checking all torque specs (got a better torque wrench from the parts store), gaskets, connections, and replace the intake manifold gaskets to see if I can correct the problem. Just would like some input on this issue as I'm still new to LS engines.
Thank in advance!!
I've been chasing an oil leak for a little bit now (last part to check is rear main), and Sunday I decided to remove my intake manifold and the valley cover to see if the leak was coming from the top end. On install, I replaced the valley cover gasket, the front knock sensor (top plastic piece broke off) with a BWD, and the knock sensor harness (original and both connectors exploded on removal). I have an LS6 intake that's been ground down on the bottom with an LS1 valley cover and coolant crossover tubes. I made sure to put a dam of RTV around the knock sensors as well.
After getting it all back together and putting 100 miles on it, my idle RPM is at 1300 and I have a bank 2 (rear) knock sensor low voltage code with slight (soft) backfires when sitting at idle.
Everything was torqued to spec, knock sensors at 15 lbs, valley cover bolts at 18 lbs, intake done at 2 passes with final torque at 15 lbs. The only vacuum lines I had to mess with was the small one (HVAC?) going to the back of the intake, brake booster (disconnected from boosted not manifold), and of course the 2 PCV lines up front.
My question is, would a loose valley cover and/or intake manifold cause a big enough vacuum leak to warrant a 1,300 RPM idle, soft backfiring, AND set off a knock sensor? I cleared the code after it first appeared, then 5 miles later it came back. Car has a slight rock to it also at idle.
I'm going to tear it down again tonight checking all torque specs (got a better torque wrench from the parts store), gaskets, connections, and replace the intake manifold gaskets to see if I can correct the problem. Just would like some input on this issue as I'm still new to LS engines.
Thank in advance!!
Last edited by FishyZ28; 11-04-2014 at 10:30 AM.
11-04-2014, 01:18 PM
#2
TECH Fanatic
Don't know about the knock sensor codes but a intake gasket leak can cause a high idle and possibly backfiring. It might be a good idea to replace the intake gaskets whiles it's apart this time.
Also this belongs in the EXTERNAL ENGINE sections.
Also this belongs in the EXTERNAL ENGINE sections.