I need help with a rough idle
Thread Starter
On The Tree
Joined: May 2002
Posts: 174
Likes: 0
From: san jose, ca
I need help with a rough idle I have been trying to pass smog the shop said the low idle failed but the high idle passed. I have removed the supercharger and headers. I did pass smog with this same setup except I was running 36lbs injectors versus 42. The thing I notice and the shop mentioned was since I pulled the supercharger and headers the car runs rough. It seems like an intermittent miss. I have changed the sparkplugs and wires and there was no change in the idle. I swapped coils and I am still having the same problem. Another thing that is weird is when I go WOT N/A I am registering 4 degrees of knock. The motor is quiet so I believe it is false knock. Also, I am running 26 degrees of timing.
I'm not sure what I should trouble shoot next. Any suggestions would be greatly appreciated.
Thanks for your time,
Jason
I'm not sure what I should trouble shoot next. Any suggestions would be greatly appreciated.
Thanks for your time,
Jason
Need more info. Low/High idle? 
Idle is not a pass/fail test. It is only a measure of your car's efficiency. Perhaps you failed the 15 MPH test and passed the 25 MPH test.
What test did the car fail, and by how much?
Are you running oem catalytic convertors?
Did you fail the "pre-test"?
Idle is not a pass/fail test. It is only a measure of your car's efficiency. Perhaps you failed the 15 MPH test and passed the 25 MPH test.
What test did the car fail, and by how much?
Are you running oem catalytic convertors?
Did you fail the "pre-test"?
TECH Addict
Joined: Nov 2001
Posts: 2,659
Likes: 1
From: Bellevue, Wa
I tune the car.
idle Ltrims are -6 - 10
well within spec. I could work a little harder to get them closer to zero, but you don't smell raw gas or anything like that and as soon as you start driving they are -1 to -2.
the car just idles rough like it has a hardcore mis. car literally shakes side to side like he had a radical cam. yet misfire counts are very low, just a few here and there that I attribute to the cam. as soon as you bring the rpms up over 1200 or so the car is smooth as can be.
the 4 degrees of knock is really weird as well. Ltrim's zero out at WOT and o2's are 900 so I don't feel it's overly rich, but the car is a dog if he gets on it.
Going to make him hook his wideband back up to be sure.
I am wondering if one the cats hasn't gone bad and is clogged up. although i don't know that this would be a symptom of a clogged cat. power loss yes, but rough idle???
There were no problems until he pulled off the blower and mac headers and put the stock stuff back on.
idle Ltrims are -6 - 10
well within spec. I could work a little harder to get them closer to zero, but you don't smell raw gas or anything like that and as soon as you start driving they are -1 to -2.
the car just idles rough like it has a hardcore mis. car literally shakes side to side like he had a radical cam. yet misfire counts are very low, just a few here and there that I attribute to the cam. as soon as you bring the rpms up over 1200 or so the car is smooth as can be.
the 4 degrees of knock is really weird as well. Ltrim's zero out at WOT and o2's are 900 so I don't feel it's overly rich, but the car is a dog if he gets on it.
Going to make him hook his wideband back up to be sure.
I am wondering if one the cats hasn't gone bad and is clogged up. although i don't know that this would be a symptom of a clogged cat. power loss yes, but rough idle???
There were no problems until he pulled off the blower and mac headers and put the stock stuff back on.
Thread Starter
On The Tree
Joined: May 2002
Posts: 174
Likes: 0
From: san jose, ca
I'm running my stock cats. They have about 52k miles on them. Hydro carbons around 300 versus being at about 150. Where I live they still only do the sniffer not the dyno. Thats why I say I failed while the car was idling.
