Can anyone help me out here. Once my car warms up I have a crappy idle, sometimes it will be fine, then the car will about stall, then it will be fine again. Happens multiple times at a stop light.

Also have a hesitation when cruising with steady throttle. It will start to bog and stutter. If I put my foot in it it will clean itself out, it bogs then goes like nothing is wrong.

I just put new oxygen sensors in it a couple hundred miles ago. Its been fine till now. Car is not driven much and has been sitting for the last month or so.

If you think this is an oxygen sensor problem what could cause my car to go through oxygen sensors so quick. I put new ones in about a year before I just put these new ones in.

 

if it's O2 related, it will throw codes--scan it. The bogging does sound like an O2 problem, if those are indeed what's wrong she's probably running really rich to go through them that fast. I suppose you could have multiple problems though--perhaps both your TPS and IAC both went out at the same time. More than likely though I'd bet on the TPS. No matter what, codes will tell the tale!

 

Oxygen sensors do not always throw codes.

TPS has the correct voltage, so its not that. I doubt its the IAC, it is clean. I have had this exact problem twice before. Once about a year ago or a little more, O2s fixed it till about 2 months ago, replaced the O2s again, it was good untill now. BLMs are split of course as with any heads/cam car.

I am at the point where I am just going to disable the O2 sensors and keep the car in open loop all the time.

After some searching I have found a lot of people have this problem with no way to fix it.

 

are you having a lot of timing retarded? knock from an unknown location?

 

No KR on showing on the datamaster when it hesitates.

No problems when in open loop, car runs and idles beautifully.

EGR tested good

No arching/bad plugs or wires

 

MAF maybe?

One of the signs of a bad MAF is negative fuel trims at idle BUT positive fuel trims at cruise.

Also check the voltage on the yellow wire with the engine running. It should be 3.7 volts or higher when you snap the throttle.

 

As of last night I disabled the computer ability to go into closed loop. Car runs better than it ever has before. Its my understanding that the MAF is still used when doing this. Can this rule it out?

 

Since you go into open loop until warm and you say it is running better than it ever has, it seems you got it into speed density mode as opposed to open loop.

Since it so easy to test it, why don't you just do that to rule it in or out?

 

So open loop = speed density mode?

The car always has run great when I first started it until it warmed up and went into closed loop. Thats when the problems began. Crappy idle/hesitation.

I will check the MAF this evening when it cools down outside a little bit and post back. Just an FYI, the screen still is in my MAF, I have never removed it.

 

OK, just went out and checked it real quick.

Idling it was around 4.3v when I snapped the throttle it went down to 3.8.

Sound right?

 

Good man. Don't EVER take the screen out. I think your test was flawed but the result is OK.

BTW open loop does not equal speed density. Speed density is just a different method of a closed loop control that does not use the MAF. If you were to remove the MAF, the closed loop control would revert to a speed density control table I believe were it relies on IAT, MAP and O2 readings for it's control. If you unplug an O2 sensor, it will go into open loop since it no longer has the final element to be able to use closed loop control. Understand? I'm sure someone will correct me if I'm wrong.

You need to look at the sensor readings when you first start it up and continue into closed loop mode with everything hooked up.

My closed loop problem was an O2 that was indicating rich all the time. My fuel pressure was holding long LONG after the engine was shut down so I felt reasonably sure none of the injectors were leaking. I had no misfires (all cylinders firing). So I knew the O2 was bad. What I thought was a rich running problem was actually a lean running problem. The fuel trims were going negative but the O2 kept saying it was rich. The injector pulse width was down as far as it could go and there were no misfires but the O2 still said it was rich. If I had a damn exhaust gas analyzer, I would have know right away that my problem was a lean condition. Then having seen the O2 reading I would know right away it was the O2 without having to bang my head for a day. LOL

 

What should the O2s be reading when the car is warming up in open loop. I will get a datamaster log and check it out.

I made the car stay in open loop by changeing the enable temp to 150*C. I cant look at the O2s readings when its in open loop set by me? I need to have it warming up towards closed loop?

When you were lean were you haveing the same sypotoms that Ive got?

Thats pretty scary. I do have a pretty rich gas smell though. I will put a fuel pressure gage on it and see how long it takes to bleed off the pressure. I know the pressure is good.

 

Optimum O2 readings I believe are around 450. Above that is rich and lower is lean. Pay close attention to other sensors as well like ETC, IAT, MAP and MAF.

 

So do I need to go back to a closed loop tune, but take these readings in open loop before it goes into closed loop? The O2s are supposed to bounce around when in closed loop normal droveing correct? Or do I have that backwards?

Thanks for all your help, I really apprciate it.