Ok guys, I've got a huge problem I've had for over a month now. Some of you that go to LS1.com might remember some of my problems but here's everything: My car idles rough, surges, misses, shoots black dust out of the exhaust, smells like half burnt solidified fuel, basically runs like sh*t. I've replaced the fuel filter, coil, and opti. No wire is burned, plugs are most likely fine but not 100% sure. Got the car scanned and it said that the passenger side O2 sensor wire rubbed through from rubbing against a bolt so I replaced the O2 sensor and electrical taped up where the wire was rubbed through. I have no idea what could be wrong here. I really need you guys' assistance! Thanks in advance for your help.

 

well just to point out the obvious, your running EXTREMELY rich.

first thing-
unplug your MAF and see whats up.
then check your fuel pressure.
then change your plugs

are your headers/manifolds glowing red?

 

Surging is usually a sign of a vacuum leak of some kind. I would check to make sure no unmetered air is coming in, and I would definitely check the intake gaskets for leaks. Also, were you able to monitor your PCM data with the new O2 sensor? That would tell you if the new one was working correctly.

 

I've checked my MAF and cleaned the sensors with a Q-Tip just in case. How can I check my fuel pressure? I have Bosch Platinum +4s I got for crazy cheap before I knew they weren't that good. Should I use them or wait and buy TR55s?

Headers aren't glowing red. Neither is cat or any other part of exhaust.

 

I haven't checked for a vacuum leak yet. I guess I will soon. My intake is leaking oil very slightly... but that couldn't cause these problems right? Just did the new O2 sensor this afternoon.

 

Any other suggestions or should I try what's been said so far and see what happens?

 

ttt for ya buddy, i hope this gets solved

 

I'll try and explain it then a little bit. When you first start your car and until it warms up it runs in open loop. During this cold idle (open loop) it's running off the stored PCM idle readings and making sure it's idling off the PCM stored values and not of the values of the sensors. When your coolent gets to a certain level, this is where your sensors will come into play. The sensors will pick up there data and send it back to the PCM where this will adjust the a/f ratio according to the values of the sensors. Also the a/c compressor has to be off (I believe it's off) in order for to go off the values of the sensors, and in manual transmissions in neutral, or automatics in drive.

Also, something I heard about is a the minimum idle air speed, which is set with a stop screw in the throttle body. This allows certain amount of air to enter the engine reguardless of the IAC position. This is unregistered air entering into your engine if its set too far out and won't allow the blades to close to their desired level that the PCM determines.

The main three sensors that could and will hurt idle (and A/F ratio in general when under 2/3 throttle or less) is the MAF, o2s and the IAC. The IAC meters the amount of air coming in through the throttle body and adjusts air flow into the engine by opening the blades up slightly. The o2 sensors will sensor your o2 reading through the exhaust and will cause the PCM to add or subtract fuel/air from the mixture to get it to read the 14.7:1 air/fuel ratio.

However, even though the PCM might believe the A/F is at 14.7:1, it might be running rich or lean due to faulty sensors, exhaust leak, ect.

The o2 sensor will pick up a lean condition, causing the PCM to add more fuel, making it run rough even though its running ok at the 14.7:1 A/F ratio.

The case with my idle problems and missing at idle and low RPMs under partial throttle was a combonation of the two. I had a faulty o2 sensor causing it to add more fuel under slight load, but under idle it wasn't adding any fuel. However, my IAC was clogged and wasn't picking up the air coming in, so the PCM opened the throttle body blades a little farther causes it to run too lean.

Best thing is to get a monitoring device, and driving around town and watch the o2 sensor readings, and the IAC counts, other sensor reading. A IAC count of 0 is the blades are fully closed, where a 140 count is fully open. I believe normal is around the 60-80 count mark. This can be monitored by a scan tool.

The mass air flow (MAF) sensor is something else to watch for. This measures the amount of air passing through it. In return the PCM adjusts the fuel delivery depending on the operating condition of the engine. A large quantity of air indicated accerlation (adds fuel), and low quantity determines idle of decleratio (subtracts fuel)

Keep in mind all sensors on board play a huge part in the a/f ratio at idle and if one is back you'll get a irratic or bad idle. Best thing to do is to monitor the sensors if you can, so you don't just replace parts that are good and waste money.

 

That's some crazy input. And you thought there might be an easy answer...

 

Thanks Braden.

That's some damn good info. My O2s and MAF are fine so how can I check my IAC?

 

The way I have always checked IACs is run "Freescan" from my laptop, which is a program that monitors the sensors and their readings. I thought there was a way to check it with a ohm meter, but I could be mistaken.

Without any tools, an easy way is to spent a 1/2 hour, take it out and just visually inspect it, if it's black, carboned up between the little coils, it might be the problem. Either way, clean it up with some q-tips and brake parts cleaner then drive around and see if that helped.

 

I'm thinking of getting Diacom soon. Would that do the same thing? Also, where is the IAC? Is it on the same side as the TPS?

 

Its on the passenger side of the throttle body.

http://csce.uark.edu/~jgbertr/rb/iac3.jpg

 

Do I have to take the tb off like in the picture to get to it or can I just take the IAC right off?

 

On mine, I removed the 4 bolts holding on the TB, but didn't remove any of the hoses. Slide it out far enough to get the torx bits in there.