Rough idle L99

[Frank in MD]

Om my way home from work Saturday night. my car seemed to have difficulty running. Idle was harsh, the tach reflected the rough idle, dipping below 500 rpm. The rough idle was accompanied by some popping from the tail pipes on acceleration but the car runs ok.

No CEL, no warning lights of any sort. I had my car in the shop previously for a misfire in cy #5 almost exactly a year ago.

Previous issue here.

about 9600 miles on the odo. Mods are catback, shorty headers w/ factory cats, CAI.

Driving her back to the shop Monday morning. Any ideas on what the deal might be?

[Frank in MD]

Well, she started out ok this morning but halfway to work she started idling rough again and the exhaust pops, gurgles and chokes up to about 20 mph then seems to smooth out.

MAF sensor? Dirty CAI? (doesn't look dirty and the car has less than 9600 miles) Fuel injectors? Maybe the coil packs again?

I've got an appointment for Wednesday morning. Very frustrated, this should not happen on a barely two year old car.

[Frank in MD]

same issue has returned. Error code U0401 and P0300. Might be trading this car is very soon.

[strych9]

I read through your other references, and it appears that a loose plug wire on #5 cyl. was the cause, correct? If so, was the plug changed at that time? If not, it could be leaking compression that would cause your plug wire to pop off over time. It's not as uncommon as one might think.

[Frank in MD]

Originally Posted by strych9

I read through your other references, and it appears that a loose plug wire on #5 cyl. was the cause, correct? If so, was the plug changed at that time? If not, it could be leaking compression that would cause your plug wire to pop off over time. It's not as uncommon as one might think.

From what I understand the tech said he swapped coil packs from 5 to 7 to see if the issue then jumped to cylinder 7. It did not reoccur so he put everything back into place and the issue did not reoccur until recently.

Leaking compression from what? Cylinder? Headers?

[Frank in MD]

So I'm going to ask for leak down and compression tests.

[thahemp]

A missing cylinder will feel rough at low RPMs and smooth out as RPMs increase. I wouldn't drive it like that though if you don't know what is wrong yet. Mine was a sheared rocker arm bolt. I limped it to my garage and tore it open before running it again.

Your shop should at least pull the valve covers if there is nothing obviously wrong with the spark plugs or wires. They should know how to troubleshoot a misfire.

[Frank in MD]

I hear you, but since this is the same symptoms as last year I don't believe I have bent rods or rocker bolts. It was the coil pack last year. Something is making it come loose, I just need to find out why.

[strych9]

Originally Posted by Frank in MD

From what I understand the tech said he swapped coil packs from 5 to 7 to see if the issue then jumped to cylinder 7. It did not reoccur so he put everything back into place and the issue did not reoccur until recently.

Leaking compression from what? Cylinder? Headers?

I should have been more clear: compression leaking through the spark plug itself. The pressure can cause the plug wire to disengage from the spark plug. Sometimes the ceramic seal inside the spark plugs fail, allowing cylinder pressure to pass through them.

[Frank in MD]

Well, the misfire is now in cylinder #4 instead of 5 as per the last issue. I'm not sure if it jumped to 4 because that's where the previous tech put the old coil pack or if this an indication of a larger issue. The svc writer inquired about my ARH shorties. That's troubling as now I get the feeling they'll say we fixed the issue and it's not covered b/c you modified your powertrain. We'll see, but as of today we still don't understand the problem or know of a permanent fix.

[RobertRS]

Do you think the headers are causing heat issue related to ignition components ? Just wondering.

[Frank in MD]

Originally Posted by RobertRS

Do you think the headers are causing heat issue related to ignition components ? Just wondering.

That's what the dealer says, and b/c of that they would not cover the $300 plus repair. I was told on the phone that the headers get hot and the wires melted/crystalized and cause the spark plug wire on #4 to crack and split. The svc writer says the protective sleeves don't make much difference if the plug wires are close to or on top of the headers.

I asked for the "melted wire" and I was presented with a cracked spark plug wire. Pics of damaged wire coming soon. Nowhere do I see heat damage inside or out.... having said that it might even be correct as this is the second time this has happened. It doesn't help that I have two different explanations from two dealers on the same issue, one year apart.

I'm looking into getting some hi temp spark plug wire and/or some type of harness that keeps a certain amount of separation between the wires and the headers.

[RobertRS]

Originally Posted by Frank in MD

That's what the dealer says, and b/c of that they would not cover the $300 plus repair. I was told on the phone that the headers get hot and the wires melted/crystalized and cause the spark plug wire on #4 to crack and split. The svc writer says the protective sleeves don't make much difference if the plug wires are close to or on top of the headers.

I asked for the "melted wire" and I was presented with a cracked spark plug wire. Pics of damaged wire coming soon. Nowhere do I see heat damage inside or out.... having said that it might even be correct as this is the second time this has happened. It doesn't help that I have two different explanations from two dealers on the same issue, one year apart.

I'm looking into getting some hi temp spark plug wire and/or some type of harness that keeps a certain amount of separation between the wires and the headers.

10-4 Frank....Maybe there is a possibility of retro fitting some sort of heat shield between the wiring and header pipes. Does the wire to header clearance seem to be consistent on both banks or are some closer as in #4 and #5 in your case?

Check these out...
http://www.ebay.com/itm/BLACK-1200-S...ee85ec&vxp=mtr

[Frank in MD]

This is the wire that was replaced. It was 90% cracked when I got it, the remainder broke while showing it.







The gaps are pretty consistent. There may be some that are closer than others but they're all relatively close.