I have an 88 305 TPI T/A that has been stalling when it reaches a certain temp...it also has a slight part throttle stumble to it....I have replace the coolant temp sensor/02 sensor /cap rotor/cleaned IAC motor/passage/new coil...still same problem....also failed emissions a few months back...
Finally got a scanner today...
I got some strange reading from the scannner...it seamed to take the car awhile to get into closed loop,but would go back into open loop after awhile...
I put the car in first and at idle I recorded this data..after allowing it to warm up a bit...
coolant temp.... 216.5 F
02 sensor...160mvolts
02 cross counts...218
Idle air steps......16
Manifold air temp 109.4 F
Injector pulse ...1.3ms
Mass air flow 4 gram/sec
02 sensor... not ready(earlier it was ready)
rich lean flag...lean
loop status...open

Looks like a bad 02 sensor I would say.....the car should not be in open loop with coolant at 216 degrees...I just replaced the 02 a couple months back...could the exhaust be clogged to give it a bad reading...(car runs great when you give it gas,its problem is part throttle/idle)so I don't think it is a clogged exhaust.


Any help would be appreciated.

 

Are you using a heated o2 sensor? Do you have headers? As far as I know the o2 sensor is not what determines if your ecm goes to closed loop, its the CTS.
What failed on the emissions? Did you get it to pass?

 

Stock manifolds...non-heated 02 sensor...have not retested the car yet for emissions...hydrocarbons failed on the test...but everything was way up from where it should be...
Earlier in the scan the 02 read as being ready putting out around 630mvolts...but then went back to not being ready and 130mvolts...
The ECM is a AC delco i put in about a year and a half ago...

 

I actually had a similar problem
Open loop to closed loop, stalling when warm.

All I did was up the min. idle a bit and never stalled since.

I dunno, it worked for me?

 

I was thinking about the injectors being bad as well....I ohmed them out and they read good...but if they are clogged it could be causing the 02 to give bad readings...

 

FWIW, my TPI switches between closed- and open-loop quite frequently while at idle. My assumption is that there isn't enough O² activity to satisfy the ECM, despite the coolant temperature.

Other possibilities are:

1. Leaking FPR;
2. Streaming injectors, causing fuel puddling;
3. Contaminated O² sensor;
4. Incorrect fuel pressure;
5. Intake air duct leakage after the MAF;
6. Vacuum leaks'
7. Incorrect fuel map (stock PROM?)

I'm sure there are more.

 

Played with it more today...I see where the 02 switches back and forth at idle...i can't find much wrong except that there is anywhere from 3-10 dgrees knock retard during heavy acceleration.....I did more data capture around idle and noticed that the engine load jumped dramatically for a second right as it was about to stall....