Hesitation and Stumbling when Cold

[seanpinoobers]

Hey there everyone. I have a mystery that might be fun to solve. So In the morning I will start up my truck and if I go to accelerate too hard the engine will bog down and hesitate and stumble like the timing is off. While it is cold but still running I advance the timing by rotating the distributor cap and I can accelerate hard and there is no hesitation. But I don't leave it like that because the actual timing (using a timing light and grounding out the ecu) was fine before I did that (about 5 - 7 degrees BTDC). Also I don't leave it like that because as it warms up, after less than 10 min of driving the hesitation and stumbling goes away. I could put the pedal all the way to the floor and it accelerates just fine after it warms up. SOoo any ideas?

[geezer101]

Idle air control valve either fouled or non functioning?

[seanpinoobers]

Okay, so this is what you are talking about? It sits right behind the throttle body looking toward the firewall.

1992-mitsubishi-mighty-max-fuel-injection-idle-air-control-valve-l4-2-4-original-equipment-w0133.jpg

[geezer101]

Yep. If it's faulty you will get idle surge. When you replace it you will need to get the ECU to go into tune mode so it can unlearn bad habits. BUT before you go out and buy the assembly make sure it's not an O2 sensor failure first or another issue. If you can read fault codes or can take it to someone who can hook up a diagnostic tool it will stop you from throwing cash at a problem without really knowing what it is. There are a number of issues that can cause an erratic idle.

[seanpinoobers]

Well technically the idle isn't the issue, It's only during acceleration. It Idle okay but when I take off from a stop light, or if I'm under the hood and I snap the throttle cable quickly it hesitates and misfires like the timing is off but the timing is set proper.