I have an 87-92 350 TBI with a 700r4. It's got less than 5k on the rebuild and it has pretty much always had issues. When cold it surges at idle, sometimes stalling out. When cold, it will bog down when you give it throttle, eventually coming to life. When warm, it will stall out on occasion when coming to stop. It will, every now and then, run strong. Here is the full background of what all I have tried:

Adjusted:

1) Adjusted the timing

Replaced:

1) Replaced the temp sensor with a new one
2) Replaced the MAP sensor with a new one
3) Replaced the IAC with a new one
4) Replaced the ignition module with a back up copy
5) Replaced the TPS with a back up copy

Tried:

1) Removed the EGR completely (and left if off)
2) Unplugged the O2 sensor (and plugged it back in after testing)
3) Unplugged the MAP sensor (and plugged it back in after testing)

Tested/investigated:

1) I sprayed starter fluid everywhere and could not find any leaks in any lines or joints. Nothing.
2) Tested the fuel pressure - steady 11 PSI at all times
3) Pinched off (with my hands) the return gas line to drive the pressure up
4) Tested the MAP pressure - and even 20
5) The PCV valve is clean and functioning

What has "helped":

1) Unplugging the MAP sensor from the ECU ended the surging right away. Interesting?
2) Advanced the timing to 0. It was off by a good 15 degrees. That ending the surging right away. But I re-enabled the advance and it wouldn't start, so I had to retard it to get it to start and, of course, the surging returned.

I have no codes in the ECU except for when I unplug something.

I am totally running out of ideas/test/things to replace. Heck, I'd re-test anything if we think it might help. I am open to any suggestions at all.

Thanks in advance.

 

Did you check the power brake booster for vacuum leaks?

 

Oops, I missed that one! I have so many non-power items and the booster hose is buried in the back, so I totally overlooked it. I will check that out tonight.

I should also point out that it's totally possible that I did a poor job at testing something. So going back and retesting or getting a second set of eyes on any element is a good thing.

 

Try getting another MAP sensor. I know you replaced it already but if you can, return it and try another one. Several of us here have had issues with those sensors even when they're "brand new". Another thing that I would recommend is to check your catalytic converter. If it's clogged trust me your car will barely run if at all. Take it to a muffler shop and they'll test it for you. Good luck!

 

Huh? You ADVANCED the timing to "0"? So it was 15 degrees retarded before that? No wonder you have problems.

Did you verify that the timing marks on the damper are accurate?

Did you verify that the computer is actually advancing the timing properly?

What is the data stream telling you when you connect a scan tool? I'd be looking at O2 voltage and cross-counts, short- and long-term fuel trim, Coolant temperature, MAP voltage, knock-sensor activity, and anything else that looked odd.