Anybody with some expert advice please. I've been trying to solve this rough idle when in gear problem. In open loop it idles as smooth as silk and when you first start it up after it's warmed up for the first few minutes is perfect too. I believe the car will always start in open loop for like 3 minutes even warm, before going to closed loop. As soon as closed loop hits, it idles rough in gear. Car idles at 550 in gear. Tach needle doesn't move and I don't think it's a miss. The following is all new: wires, plugs, coil, PVC, MAP, TPS, O2's, cleaned IAC and checked. Vacuum leaks checked and none. TB and intake has been cleaned. It did it before the headers were installed also, so I think I can eliminate exhaust leaks. I'm down to thinking it's because of the ported MAF or original opti. I don't think opti because it's fine in open loop. Putting the screen back in the MAF didn't change anything either. Other than the idle the car runs flawless with no hesitations. Any other suggestions to check on?

 

I would say try to borrow someone's MAF and see if it idles better.

 

Not really an option for me since I just moved to the area and don't know anyone. Can I unplug my MAF when it's in closed loop? Will it go into speed density mode and check that way or will it run like crap and throw codes?

 

Well it might throw a code for your MAF but yes you would go into open loop and it shouldn't have a rough idle.

Some parts stores let you buy the part and if it turns out that wasn't what was wrong they let you return it as long as you do it within a couple of hours.

 

My car did the same thing, and we figured out it was the Opti. It would start up and run just fine in open loop, then once it hit the Closed it started to hesitate, and sputter.

 

Scan it and see if it throws any codes. Then you'll have an idea.

 

I guess I need an elementary lesson on open-loop, closed loop. My understanding is that the ECM is in closed-loop at idle and open loop when pedal to the metal. I.e, the ECM tries to maintain optimum A/F in closed loop but in open loop the maping takes over and along with the throttle position and 02s the ECM provides optimum A/F based on conditions.

I'm hearing you say that its in open loop when you start it up. Probably a misunderstanding on my part.

I will say that when I first had my A/F optimized by Ed for my small cam everything was fine, but I did realize a bit better idle with PCMFORLESS when I had the heads done and Brian did some A/F tuning for the idling as well.

It seems to idle a bit nicer since Brian did some programming for idle as well as WOT.

So someone please set me straight on the closed loop vs open loop condition.

Thx.

 

open loop on start up and at WOT

closed loop during normal driving

that was my understanding

 

Open loop it is running off of some basic sensors and the tables. Closed loop requires your oxygen sensors to have heated up. Once they are heated and you go into closed loop the computer trys to compensate for the a/f ratio. WOT is also open loop. It stops reading the O2 at WOT. This is why dyno tuning for WOT is so helpfull.


Ben

 

Yea. I guess it would be in Open Loop on start up until the 02s had a chance to warm up. Seems though that as soon as the 02 warmed up and the ECM went into closed loop (for idling and normal cruising) that either the 02s need some work, or the ECM needs some A/F programing for closed-loop operation to maintain a smooth idle.

I obviously don't know what I'm talking about, but...

 

Could the ported MAF have anything to do with it?

It's obviously not calibrated and may not work optimally with prgramming.

Hell, I don;t know. Good luck, and tell us what you find out.

 

Have you tried using a scan tool? It sounds like your O2 sensors might be fouled. I see you have replaced them, but you need to check the mV readings to see that they are operating correctly. If one bank looks different than the other, check for burnt plug wires first (common when installing headers), then swap out that particular O2 sensor. Hope this helps.

JR

 

Well, I just reread what Vizard said, and he says that the overlap stuff doesnt work on the street. He did say that on race motors with enough overlap that the exhaust scavenging during overlap(while both valves are open) pulls more intake air into the cylinder. He said that on the budget motor that he was using as an example it exerted what would be equal to 1 psi of force on the intake air, but in winston cup motors it exerts what would equal to 6 or 7 psi. He says "In practice, then, the exhaust phenomena makes a race engine a five-cycle engine with two consecutive induction events."

He also states that you can get a wider powerband with the correct exhaust diameter. I dont know the 3" collector with the reducer effects all of this though.

Ben

 

Say what?

 

It doesnt matter. Other than the fact that I still dont believe that all motors need dual 3" pipe or could all benifit from it, the rest of it just applies to racing motors for the most part. If I would have realized that before I posted it I wouldnt have bothered.

Ben