I have been fighting this issue for a couple of months. Trying to sell the car but I want it to be "right" when I do.

I start the car, it fires right up and idles smooth, no misses. Put it in gear and it either stumbles right away, or as soon as I hit the gas. It feels like it is gonna stall but I let off the gas and it starts moving then I can give it gas slowly. When I get in closed loop mode everything is perfect. I can stomp it right from a dead stop, or anywhere in the RPM range, and all is fine. I don't have a scanner but I haven't got any ser. Eng. lights the whole time I've had this problem.

Here is what I have changed so far:
installed TPI Fuel pump and new filter
plug wires/ cap/ rotor button ( a couple wires were chaffed so I changed 'em all)
new TPS
cleaned IAC

 

it sounds like a fuel pressure problem. too rich when cold. possibly too much fuel pressure that the int and blm have adjusted for when warm. any trouble on a warm restart?. search for the ohm check on a ect sensor. there was a resistance table posted for it but i dont remember where.

 

Rocko, no problem at all on a warm restart.

 

Did it do it before the modifications or just after. Also after the modifications, has it run normally and just started acting up?

Finally for grins, put a CTS in it. The last one I bought was under $10.00, and they are located right up top by the thermostat housing. The CTS is a common failure on high mileage GM vehicles. I have seen them read 100+*F on a 40* day, prior to a cold start. What happens there is the cold engine needs more fuel, but the ECM thinks the engine is already 120*F and it does not get it. This causes the engine to hesitate and stumble. Then as the engine temperature increases, the problem goes away.

 

Fast, the problems started before the mods. The mods were a result of me chasing the problem. I will try the CTS, that is one of the things I haven't tried. Does the CTS or the fan switch provide the guage its signal? The temp guage seems to be acting correctly.

On the tech board someone said the base timing may be retarded, and I will check that too, but the way you explained how the CTS operates on startup sounds like that may be my fix.

 

Wasn't the CTS. Still have to check timing.

 

sometimes the connector on the coolant temp. sensor fails causing the vehicle to malfunction like the CTS is malfunctioning, no check engine light on or anything?

 

Nope, never a check engine light.

 

I know this is super old but I am experiencing this same problem. As this thread has already been started but not completed, I'm hoping to revitalize this and hoping that after nearly 20 years, perhaps folks have found solutions.

Thanks!!

-Chris

 

WHAT VEHICLE??? Why wouldn't you tell us what you're working on?

AFTER connecting the scan tool to interrogate the computer, consider disconnecting the battery or pulling the ECM fuse(s) to give the computer amnesia--and "restart" the computer from it's base tables instead of whatever it's "learned".

The Usual Three:

1. Verify fuel pressure at prime, at idle, and under load. Most fuel pressure gauge assemblies have a push-button pressure release connected to crappy vinyl tubing. Route the tubing so it empties into a drain pan, then push the button while the engine is running. This simulates higher fuel demand if you can't check fuel pressure on the highway. Fuel pressure should remain steady even with fuel flowing down the pressure-relief tubing. TBI systems don't hold pressure when the pump stops running, but the other fuel injection styles should. How old is the fuel filter? Have you ever dumped a bottle of Chevron Techron Complete Fuel System Cleaner into the gas tank? (Recommended at every oil change.)
   
2. How old are the usual “tune-up” parts and procedures? Inspect/replace distributor cap, rotor, plug wires, spark plugs. Use quality parts sourced from an authorized seller (NO COUNTERFEIT PARTS FROM AMAZON, EBAY, OR OTHER SKETCHY SELLERS!) Be sure the ignition coil will reliably fire a spark-tester calibrated for HEI when the coil is fully warm, and misted with water from a squirt-bottle. Cranking compression test of all cylinders while the spark plugs are removed. Verify EGR, PCV, EVAP, and Heated Air Intake (if used) systems for proper operation. Verify proper initial timing (TBI) and electronic spark advance (TBI and Vortec). Replace old O2 sensors unless you can PROVE that they're working properly—old O2 sensors get lazy, they don't provide accurate data, but they do provide “data” that fools people into thinking they're “working”.
   
3. Connect a scan tool (NOT a crappy “code reader”) and look for “codes”. More important, look at the data stream to verify EVERY sensor and computer output. Verify fuel trims during the time that the vehicle is not running properly. Look for misfire counts for each cylinder (OBD2 only.) “Codes” have official diagnostic procedures that will be found in the service manual set for your vehicle.

 

Thanks @Schurkey for the breakdown. Ended up being a restriction in the fuel filter and a failing fuel pump. After connecting the Moates ALDL cable and running Tunerpro RT I was able to see the BLM's and INT shooting way hi.

After rebuilding the TBI, completing the TBI mods to include an adjustable fuel regulator, injector pod spacer, replacing the fuel sending unit, fuel pump and fuel filter and adding a fuel pressure gauge this problem was more than resolved and finally running nicely again.