My car idles rough, and hesitates in the lower RPMs (idle to 1500-1800 or so). If I hold the RPM's at anywhere from 1000-1800 in neutral, they drop and go back and forth and the engine stumbles.

The car still pulls hard at WOT....

Here's the deal though, once I unplug the O2 sensors, it runs like a dream, so I know it's not opti/ignition/fuel related, or even a vacuum leak. Even after I replaced the O2 sensors with brand new AC delco ones, it still has done this. My passenger side band clamp on the slip-fit collector does not leak at all, and the driver side has a VERY tiny leak. So small that you can't even hear it, but if you put your hand beside it, you can feel a TINY bit of air coming out.

Every once in awhile the car will run just fine, and will idle great....then the longer it idles, it starts idling rougher again.

I don't think the exhaust leak is big enough to make it run rough like this. The difference between the car with the O2s plugged in and the O2s unplugged is night and day. I can't even feel it running with them unplugged.

Could it be a tuning issue?

Please help....

Thanks in advance,
Matt

 

???

What?

 

That's what I'm thinking....I don't think I have a leaking header gasket though, because that would be pretty obvious. I'm gonna have a friend hook up a scanner this weekend.

 

Did I do something wrong? It seems like my posts always work their way a few pages back and get numerous views and not many replies.

 

dont feel bad mine gets the same treatment. next time ask about which catback you should get and at least someone will tell you to use the search lol

 

FYI, I do not modify part throttle tables on stock or bolt on cars. I do some timing changes but they are close to WOT area.
I'd clean up the MAF, check for vacuum leaks, etc... the usual stuff.

 

But it couldn't be the MAF and it's definitely not a vacuum leak because it runs perfect with the O2's unplugged....

 

You can send the PCM back and I'll put a stock tune on it for you to try if you want. I can guarantee there is nothing with the program that would cause what you're describing though.

The only way this would be the program or PCM is if this started the same day you put in the programmed PCM.

 

PS I wasn't blaming it on your tune, I was just asking if it could be tune-related or if it's the exhaust leaks throwing off the O2 readings.

*EDIT* I still have my stock PCM. I could swap it in, I'm just asking if tuning can help the situation.

I'm gonna hook up a friend's scanner this Saturday and let you know what happens.

 

I doubt you'll see anything helpful on the scanner.
Put in the stock PCM just to see what happens, then let us know.
Also, you didn't say when all this started...

 

Well, the car was running perfect after my header install (new O2s, plugs, wires). 2 weeks later, my O2's crapped out and the car would barely run in closed loop. I replaced them, and it has still had a rough idle ever since I put them in.

Atljar told me that if the exhaust leak is messing with the O2 readings, that the voltage would come up low.

 

Just because you unplugged the O2s and it runs fine, doesn't mean you don't have a Maf or other problem. Let's say you have a vacuum leak. It should run lean until the pcm corrects for it. Unplugging the O2s should make it rich as it will be in Open loop. That might correct for the unmetered air and cause it to run fine. Try disconnecting the MAF with the engine off and the O2s plugged in. It will be in s/d mode and you will get a ses light but it might give you a clue. Just an idea.

 

I already ran the car w/the MAF unplugged and noticed no difference.

 

If it throws a code it could be the MAP sensor, the air temp sensor, coolant sensor, etc. See what the scanner has to say.

 

Tonight my car ran:

13.5@103 2.0 60'
13.5@103 1.9 60'
13.5@103 2.0 60' - cutout open
13.4@103 1.9 60' - cutout closed
13.5@103 2.0 60'

So we know it's running hard at WOT....getting it scanned tomorrow. I think it's the O2's.


For those of you who care, 29.94 baro, 90 degrees, 85% humidity, 28psi in my BFG's dead hooking every time with the pedal to the floor.