I have posted this before and still haven't gotten it fixed yet. I have a 93 vert 6sp, 383. It has always ran great but recently has developed a rich stumble when it goes closed loop. It has never set a code, which I wish it would. It never hesitates to start. Runs perfect in open loop and if I let sit and idle as it transitions into closed loop you don't notice anything differant. The O2's kick in and start bouncing back and forth between 400-600, still idleing great. Now after it's in closed loop if I hit the throttle hard it comes back down to idle and almost stalls but never does, it idles back up but now it will have the rich stumble. The O2's now stay up in the 900's telling the ECM that its running to rich I assume and cutting the fuel back.

I do have a Helms manual and have been using it like a madman. I do have a Auto Xray 5000 scanner but it's not a tech 1 so I can't do all of the troubleshooting like the helms tells you to do. I swore I would not just throw parts at it to try and fix it but slowly over the last couple of weeks I have replaced the following:

IAC, TPS, O2's, Coolant Temp sensor, fuel filter, new plugs, All Opti parts are fairly new, and I just installed new EM long tubes and random Tech cats (Headers kind of unrelated to the problem I just wanted them). Now when I replaced the TPS I didn't have a Tech 1 to initiate the learn process for this. Is this something that could affect it only when it goes closed loop and do I need to find a Tech 1 to do this?

Any help or suggestions would be appreciated!!

 

-the cars PCM will initiate the "learn" process.
-the idle is pre-programmed in the computer, the TPS voltage is used by computer soley for throttle response(ie A/F ratio adjusted at any given TPS voltage)

What the Throttle Position Sensor is:

The throttle position sensor (TPS) on the throttle body is a little known yet very key sensor. The TPS tells the computer what position the throttle blade is at; from this, the computer can see how to control timing/fuel as well as shift points for the transmission. The TPS is a resistor sensor, it will alter a 5 volt input based on its position and send that output voltage to the PCM, which will inturn recognize the voltage as a percentage of throttle opening.

Things to take note of:

To perform the "TPS learn procedure" upon first startup, turn the key to on, wait 30 seconds, then turn the key off. Now start the vehicle and let the idle learn.
The engine may idle high for the first few startups, especially if the computer hasn't been reset. This is normal and it will learn the idle adjustments needed to reach factory desired idle speed.

 

How old are the O2's? 400 - 600 is a narrow range of oscillation. Might think about replacing them. If you do, I'd go with Denso instead of Delco.

 

MikeC4- Good info but I've had the new TPS in for a little while and it should have learned by now besides it only has the problem when it goes closed loop and I hit the throttle hard.

Lone Ranger- The O2's are brand new but I used Bosche. I know they are cheaper but they should still be good.

 

My Bosch O2's were bad from the git go. There are some things on these cars that really need stock parts reguardless of cost.
1.Anything that requires a lot of time and effort to replace.
2.Opti
3.O2 sensors
I learned this lesson the hard way.My car ran lean with the Bosch's in runs fine with GM.
If your car runs good in open loop then the likely candidate for the closed loop difference is the O2s.

 

I think I may run and get some stock O2's and try that out, I don't know what else it could be to make it run like crap only once it hits closed loop, soon to find out though.

 

...good point on the O2 sensors. I had error code which pointed to the drivers side O2. When I pulled it out, it was a Bosch. I replaced with OEM sensor and my CL operation improved dramatically. Caveat to this is that I have heard/read that the AC Delco O2 is supplied by Bosch.....don't know if this is accurate or not...