another noob question about rough idle
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WOW thank you all so much for your support. It makes a huge difference. On the cats idea, could they cause a rough idle issue? One thing that has been happening since i bought the vehicle is that when i really get on it, and the rpms go above 4500 there is a rattling sound coming from what seems to be the exhaust. I only run chevron 91 so i didnt think it knock at least not from gas but i read where someones vette did the same thing as mine with the rattling under load and it was their cat was bad. So i ask again, could a problem with a cat cause a rough idle? is there a way of testing to see if that is the issue, i am going to devote all of saturday to trying out these ideas that have been givin since last saturday so any ideas would be great thank you all again
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Joined: Jan 2007
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From: Dyer, IN
WOW thank you all so much for your support. It makes a huge difference. On the cats idea, could they cause a rough idle issue? One thing that has been happening since i bought the vehicle is that when i really get on it, and the rpms go above 4500 there is a rattling sound coming from what seems to be the exhaust. I only run chevron 91 so i didnt think it knock at least not from gas but i read where someones vette did the same thing as mine with the rattling under load and it was their cat was bad. So i ask again, could a problem with a cat cause a rough idle? is there a way of testing to see if that is the issue, i am going to devote all of saturday to trying out these ideas that have been givin since last saturday so any ideas would be great thank you all again
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From: Fort Worth, Texas
True, but I'm having the same problem as the OP it sounds like and have checked everything he has. I'm thinking they have "partially" failed(mine seems to be more intermittent), going to straight pipes soon and will find out for sure. It makes sense because the lessened flow will cause reversion and the rough idle. When rpms speed up, it'll worsen causing the detonation from a diluted intake charge. I agree you should notice the power loss, I'm going to the track tomorrow to see. Jon does it get better initially when you reset the pcm by pulling the fuse?
Last edited by PRE-Z06; Aug 27, 2009 at 09:55 PM.
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ok, so i did what you said, i pulled the fuse for the pcm. Didnt seem to make a difference unless i did something wrong. All i did is when the car was off i pulled the fuse out and put it back in. A sneaking suspicion says i did it wrong. please let me know
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From: Fort Worth, Texas
hmmm, that's all you do to clear the memory. I just got back from the track and trapped 120mph on street tires, so it seems to be running ok...I'll let you know more once I get the cats removed.
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ok, so i took it down to a local corvette guru and he hooked it up to his tech 2. The car was doing the rough idle thing the whole time he was scanning. Fuel trims were perfect, o2 sensors were behaving normally, MAF was working fine, everything was running great. he said the engine sounded nice and smooth, he took a ride in it and said it was pulling fine in all the gears and at all rpm ranges, there was an old MAF code so he is gonna swap my maf for his and let me drive it for a day or two and see if that may make a difference so we shall see.
Drifting
Joined: May 2005
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From: Littleton Colorado
Forget the cats idea. More than likely removing them will help nothing, and its a LOT of work and $. Cats really are not a source of issues.
There are several sensors that are involved in the fuel management for your Vette, the front O2s, the MAF, the Intake Air Temp, Engine Coolant Temp, and Manifold Air Pressure. Any one of these sending in incorrect data can make your engine run rough. Did your friend check the ECT, IAT and MAP values when they scanned? Next any slight air leak can cause a problem. The air bridge can be deceiving, it can look like its on but it will not always be on. Also, it has two pieces and you can develop a leak at the joint. I'd triple check every thing before dumping any more money into it. Next, the PCV system does have a connection at the throttle and it can leak. The only vacuum connection is at the back of the intake. You have the brake booster and then the vac line that actuates the routing of air in the cabin. If the brakes are fine and you can switch your AC from the floor to any other position, then those systems are OK.
Good luck with it.
There are several sensors that are involved in the fuel management for your Vette, the front O2s, the MAF, the Intake Air Temp, Engine Coolant Temp, and Manifold Air Pressure. Any one of these sending in incorrect data can make your engine run rough. Did your friend check the ECT, IAT and MAP values when they scanned? Next any slight air leak can cause a problem. The air bridge can be deceiving, it can look like its on but it will not always be on. Also, it has two pieces and you can develop a leak at the joint. I'd triple check every thing before dumping any more money into it. Next, the PCV system does have a connection at the throttle and it can leak. The only vacuum connection is at the back of the intake. You have the brake booster and then the vac line that actuates the routing of air in the cabin. If the brakes are fine and you can switch your AC from the floor to any other position, then those systems are OK.
Good luck with it.
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Ya, he did scan those values as well, also i just replaced the pcv and the vacuum hose that connects it to the intake. It was cracked. Still didnt solve anything. I tried the old starter fluid test on all the connections from the MAF back to see if any cracks existed and none were obvious. Also i am able to change the ac from floor to the others, even tho all it does is blow hot air out at this time. Another project for next summer lol
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From: DEXTER NM
My 2004 has what I consider a "rough idle" since the day I brought it home....Someone posted about the stock LS1 having a "shivery" idle, and this describes mine exactly!
"- First, the stock LS1 has a characteristically "shivery idle"....not rough but shivery......another way to describe it is stable RPMs with a slight "tremor". I have a 2001 LS1, A4 and it idles nicely at 500 RPMs in drive when warm. Are you sure it's just not shivery?"
I glad I found this tidbit of info, so I can finally forget about my rough idle woes...
"- First, the stock LS1 has a characteristically "shivery idle"....not rough but shivery......another way to describe it is stable RPMs with a slight "tremor". I have a 2001 LS1, A4 and it idles nicely at 500 RPMs in drive when warm. Are you sure it's just not shivery?"
I glad I found this tidbit of info, so I can finally forget about my rough idle woes...
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Ok, i will do that once i am home tonight, this only started happening about 5000 miles ago, it idled infinitely better before, still it had that minor shiver like everyone described but not the roughness it has now.
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From: Fort Worth, Texas