87 Runs poorly when cold

[GM 4 Life]

My 87 has a rebuilt older "orange motor" 305 in it w/ the complete 87 tbi setup on it installed from the po.It also has the 700r4 & 2:73 gears. The motor has less than 1,000 mi. on it. It has a new complete tune up, egr valve, coolant sensor, rebuilt tbi, new vac. lines, new fuel pumps & filter. I also verified the timing.When cold it fires right up, but then starts idling down roughly & stalls if I dont keep feathering the throttle @ 1,800 RPM'S or so. It also runs rough while driving /stopping untill it warms up. When it does die it always fires right back up. Once warm it smoothes out somewhat & has good power/pick up w/ no stalling, but its not what I'd call perfect.The outside temp. seems to have no factor on this issue. The fuel injectors werent replaced on the tbi rebuild & they have 255,000 mi. on them. Could that be whats causing this or could it be one of the emission sensors? I am @ a loss here & dont want to start expensive parts swapping on a whim. Thanks in advance.

[Jonboy]

You might try the 88-98 board. There are some sharp TBI guys over there, that generally don't come over here much.

[jonessmc87]

probably a bad temperature sensor. Its telling the computer that it is warm all the time and therefore it is too lean when it is cold. If the sensor was working properly the computer would know that the engine is cold and would richen up the mixture. Instead, its your right foot keeping it running until it warms up and then the "lean" mixture is the right mixture to keep it happy.

[rfmaster]

Originally Posted by GM 4 Life

My 87 has a rebuilt older "orange motor" 305 in it w/ the complete 87 tbi setup on it installed from the po.It also has the 700r4 & 2:73 gears. The motor has less than 1,000 mi. on it. It has a new complete tune up, egr valve, coolant sensor, rebuilt tbi, new vac. lines, new fuel pumps & filter. I also verified the timing.When cold it fires right up, but then starts idling down roughly & stalls if I dont keep feathering the throttle @ 1,800 RPM'S or so. It also runs rough while driving /stopping untill it warms up. When it does die it always fires right back up. Once warm it smoothes out somewhat & has good power/pick up w/ no stalling, but its not what I'd call perfect.The outside temp. seems to have no factor on this issue. The fuel injectors werent replaced on the tbi rebuild & they have 255,000 mi. on them. Could that be whats causing this or could it be one of the emission sensors? I am @ a loss here & dont want to start expensive parts swapping on a whim. Thanks in advance.

You may have low fuel pressure. Stock TBI is spec at 9 to 13 PSI. TBI will run with as little as 6 PSI but poorly! When CTS reports low temperature (cold) ECM will try to add fuel, but with low fuel pressure it may have hard time supplying enough fuel to a cold engine. During cold start only CTS and TPS are used - O2 sensor is ignored for the first 2 minutes (and while CTS is below 45C).

Check Fuel pressure (and fuel filter) - It is common for fuel pumps to get tired after 24 years in service (255k miles).

//RF

[chevymotocross]

I've had the same issue with my 87 305 tbi and still do to this day. Worse when it's really cold out. I replaced the CTS with no luck. I believe it actually started doing this after I installed the TBI spacer. Not positive but I don't remember the issue before that install.

Once it gets up to temp, idles and runs great. Sounds like I have a lumpy cam on the first initial few minutes.

Fuel pressure is also at 13.5 psi