my 90 bird 3.1 takes a while to start on the first start of the day regardless of ambient temp. Once it starts it takes a couple seconds almost like it is refilling the fuel system. it runs really rough at idle. Driving is fine tons of power ( for what it is ) runs great and smooth at any thing not idling.


I have

changed the injectors

fuel filter

fuel reg

egr valve

air filter.

coolant temp sensor

checked all the vac lines

re set the timing to 12 btdc

new cap and rotor

new 195 thermostat.


any ideas. I can hear the fuel pump priming when I turn the key on and from what I understand about e pumps is they either work or they don’t. Is there ever a case where they don’t pump enough at idle. Car has 146k pretty sure that’s the original pump. It has never stalled or died just runs rough

any hints or ideas would be great.

 

Doesn’t sound like the proper timing for a 3.1, what happens to fuel pressure during prime ? Peaks to above 40 and holds ?

 

As tuned performance said, check your fuel pressure. There's a valve for checking it on top of where the fuel lines go into the rail. If you haven't tried it already, hop on youtube and find a tutorial on checking your codes on an OBD1 GM ECU.

After that (assuming it doesn't give you your answer) I'd check your IAC. After a while the plug itself and the passages get clogged with carbon and can mess with your idle. I'd recommend taking the valve itself and the passage off and cleaning them both with throttle body cleaner. While you're at it make sure the IAC valve is working properly. There's a video on youtube that goes over diagnosing and resetting them as well.

Next, there's quite a few sensors on there that the computer reads to determine AFR and if any one of them is bad or not connected properly you're gonna get a rough idle. You've already replaced the coolant temp sensor so that's probably fine, but also check your O2 sensor, intake air temp sensor, and your MAP sensor. They should all be on the passenger side of the engine, and the MAP is on the firewall with a vacuum line going to the intake manifold.