I have been searching for answers about my car problems on this site and am impressed with all of the help.

I have a 305 TPI automatic. It has a stall/cut back or hesitation after applying throttle while cruising. at a light or under load - going up a hill. It has also had irratic idle. Here is what I have done and it still isn't better. It seems to do it most after heating up - 20 minutes of driving.

New: O2 sensor, IAC, TPS, coil, ignition module, MAS, fuel injectors, gaskets, fuel regulator, EGR (now disconnected and capped at EGR and EGR solenoid), plugs, wires, cap/rotor.

The fuel pressure and fuel flow are within spec.

I am now clueless? Any ideas?
Thanks,
Jim

 

Welcome Aboard! And welcome to the ranks of the clueless - You are not alone.

You've apparently already addressed the usual suspects. What is the standing fuel pressure?

What spark plugs and at what gap?

Is the ESC connected and not retarding spark?

Base timing set at ???

Cam specs?

Idle vacuum reading?

 

Hey thanks!
The fuel pressure, idle vacuum, timing and stock cam are within specs. I don't know about the ESC and timing retarding correctly?

Plugs are AC delco and set at .035, if I recall correctly (what ever the book called for). I forget what the base timing is set at, a GM auto shop just reset it. Basically, they spent 2 hours ($175) on the car and could not figure it out. They said maybe another 2 hours and they could figure it out.

Since it operates perfectly until it get to max running temp I am starting to wonder if there is some part failing after it gets hot. The idle vacuum, even after the car is hot, still does not act like a vacuum leak and and can't hear one. Could it be a head gasket? Fuel pump wearing out after 20 to 30 minutes of use?

Thanks so much for the help. This car is like new - except for this issue. Frustrating!

 

I was actually hoping for definite readings, instead of "in specs". The specified ranges of the variables can be a little broad, and error can be cumulative. If it were on the low end of the idle vacuum specification, but at the high end of the idle RPM specification, and the fuel pressure at the low end of the spec, with the O² at the low end of the spec, it could be running quite lean and still not set error codes.

The thermal issues could include the pickup coil and reluctor, ignition coil, HEI switching module, EST module, ignition primary power and general ground connections, ECM output transistor problems, ECM connections, injector coil resistance and conductivity, and probably numerous others.

Your description of the symptoms could indicate a lean condition and/or weak ignition.

 

Thanks again. Unfortunately, we are starting to get beyond my "backyard" mechanic ability. I guess its back to the shop. I just hope they can figure it out!