Idle Misfire
Thread Starter
Staging Lane
Joined: Mar 2008
Posts: 89
Likes: 0
From: Michigan
Idle Misfire My car is missing at idle and only at idle. I took it to a shop and they put it on the dyno. They are saying throughout the rest of the power band it doesn't really miss at all. They told me that they think I have a clogged injector and to run seafoam in the gas tank for the next 1000 miles to see if it dislodges it. Does this sound right or what???????
TECH Regular
Joined: Dec 2005
Posts: 437
Likes: 9
From: Indianapolis
Check your plugs and wires. It could be a clogged injector but it's not real common if your running 93 gas in it. Shell and a few other stations have an additive in it already and some stations have ethonal blend in it which really cleans things out. I had the opposite of you with a missfire under load/accel and it was a cracked plug.
TECH Regular
Joined: Dec 2005
Posts: 437
Likes: 9
From: Indianapolis
No if it misses all the time it will throw an SES code and you can track down what cylinder it is in. Mine never threw a code and idled perfectly and did WOT perfectly, it was while the car was getting up to speed or on the highway it would miss. A bad plug or wire causes some wierd **** to go down.
TECH Fanatic
Joined: Aug 2006
Posts: 1,407
Likes: 63
From: Knappa, Oregon
No if it misses all the time it will throw an SES code and you can track down what cylinder it is in. Mine never threw a code and idled perfectly and did WOT perfectly, it was while the car was getting up to speed or on the highway it would miss. A bad plug or wire causes some wierd **** to go down.
Plugs and wires are the main cause of all misfires. When were your's changed last? 
Staging Lane
Joined: Jun 2008
Posts: 78
Likes: 0
i got the same problem but my car is cammed it has misfire on all 8 cylinders at 825rpm as soon as you bring it to 900-950rpms the misfire goes away i've put new plugs and wires and nothing, my mechanic said its normal that the
LS1 with a cam will due that on very low rpms
LS1 with a cam will due that on very low rpms
Staging Lane
Joined: Jun 2008
Posts: 78
Likes: 0
found some info if you're car is cammed
http://ls1howto.com/index.php?article=23
"- If you have a check engine light, use an autotap scanner to pull the codes. A common code at this point is P0300 (Random Misfires), and may happen from time to time when idling depending on the size of your camshaft. This is nothing to worry about, and if it bugs you, tuning can get rid of it."
http://ls1howto.com/index.php?article=23
"- If you have a check engine light, use an autotap scanner to pull the codes. A common code at this point is P0300 (Random Misfires), and may happen from time to time when idling depending on the size of your camshaft. This is nothing to worry about, and if it bugs you, tuning can get rid of it."
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Thread Starter
Staging Lane
Joined: Mar 2008
Posts: 89
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From: Michigan
My car isn't cammed but I am going to go ahead and change the plugs and wires. I have already pulled them all out. One was cracked but that may have happened when I was trying to loosen it. All of them are black on the end and I believe they are the original plugs and wires that came with the car. What plugs and wires should I go with?
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I had this problem and changed plugs and wires and the problem stayed. After messing around with everything I decided to change my front O2 sensors. Now my car has no misses and idles as smooth as glass.
TECH Regular
Joined: Dec 2005
Posts: 437
Likes: 9
From: Indianapolis
Look in the sales thread there are plenty of MSD wires plus free NGK TR55 plugs. Those are widely accepted here as the choice plug. Basicly your paying for just the wires and you get free shipping. Front O2's you should (in theory) notice some other issues like sluggish accel.
Thread Starter
Staging Lane
Joined: Mar 2008
Posts: 89
Likes: 0
From: Michigan
I wouldn't worry about it but it sets my SES light off and says the bulk of the misfires are in cylinder 7. Should I be pulling the heads to determine if there is a valve issue. A few months back I bent a couple of pushrods.
Might try swapping external stuff first, like the
#7 injector with #5, same for coil, wire & plug;
one thing at a time, Looking for the misfire location
to move. The heads can always come off later.
Believe I've seen somewhere that the misfire
may be mis-reported for location. You might try
running cylinder balance tests etc. to get some
confirmation on the bad site.
#7 injector with #5, same for coil, wire & plug;
one thing at a time, Looking for the misfire location
to move. The heads can always come off later.
Believe I've seen somewhere that the misfire
may be mis-reported for location. You might try
running cylinder balance tests etc. to get some
confirmation on the bad site.
TECH Fanatic
Joined: Aug 2006
Posts: 1,407
Likes: 63
From: Knappa, Oregon
Thread Starter
Staging Lane
Joined: Mar 2008
Posts: 89
Likes: 0
From: Michigan
I've been told that the vehicle does run rich. I don't really smell any gas. I've also had a compression test done and the number 7 cylinder is lower than all the others most of the time.