87 caprice 305 running issues when cold

[bracketshark]

Customers car. The car only has 70,000 miles on it and has been running great up until few days ago. The choke works great, the car will crank up cold and idle fine, the problem is when trying to drive the car within 5 minutes of cold start up, it acts like its running out of fuel when accelerating. When this occures it will still idle fine. After the 5 minutes or so of messing with it and thinking it just isn't going to run, the car will run perfect, acceration and all. We have installed new distributor cap and button, new fuel pump and filter. I swaped in another map sensor and disconnected the EGR with no noticable differance. I forgot to mention the carb. is one of the electronic controlled Q-jets. Any information will be helpful. Thanks.

[j cAT]

Originally Posted by bracketshark

Customers car. The car only has 70,000 miles on it and has been running great up until few days ago. The choke works great, the car will crank up cold and idle fine, the problem is when trying to drive the car within 5 minutes of cold start up, it acts like its running out of fuel when accelerating. When this occures it will still idle fine. After the 5 minutes or so of messing with it and thinking it just isn't going to run, the car will run perfect, acceration and all. We have installed new distributor cap and button, new fuel pump and filter. I swaped in another map sensor and disconnected the EGR with no noticable differance. I forgot to mention the carb. is one of the electronic controlled Q-jets. Any information will be helpful. Thanks.

with that cold air down your way this is where the carb , choke adjustment to be correct...with the electric choke in the chevy 305 quadrajet the bi metal heat choke spring gets weak and as a result drops out too soon....replace the electric choke ...

I have had to do this several times...a little way to get around buying a new one if you cannot locate part is to modify the choke so that there is more choke ...this is done by filing down the plastic key and rotate about 1/8 in..

[LoveMyChevy]

Like he said it is most likely the carb. I have the same car, same year, same carb, same engine size and the same problem. Rebuild and clean carb and replace electric choke. ( I dont expect you to do this yourself so if you have funds then go to a reputable shop) Shouldn't be more then $250 for professional rebuild and cleaned carb with new electric choke.

Not a bad idea to replace plugs and plug wires also. Check for vacuume leaks too.

[caffeineaholic]

Another possibility may be the THERMAC system's vacuum motor; if it is not the main cause of the problem it could be part of it. The snorkel coming out of the air filter should have a vacuum diaphragm and it will actuate when it is cold (so long as the temp sensor in the THERMAC assembly is good).

This heats the intake air because some/most is taken from air around the exhaust. Lastly, there should be a tube going from the bottom of that snorkel to a metal piece near the engine's exhaust manifold.

This page may be of assistance: http://www.73-87.com/7387garage/drivetrain/thermac.htm

My 85 305ci Caprice has issues in the cold because the temp sensor does not work right (costs too much for me to replace currently). It will stall and be sluggish until about 3-5 mins of warming up on cold days.