I am at my wits end with this thing. It seems so common for people to have the OPPOSITE problem, where their truck runs rough when warm. But for me it runs rough when COLD. I have to feather the gas pedal to keep it alive for a few minutes and eventually the RPMs stop dive bombing and it stays alive on its own. Dont want to have to do that - something is not right. Chain of events: Ran beautifully off the boat. Drove for 6monts and wouldn't fire one day. First assumed it was fuel pump so I replaced that. No dice. Then I figured out that the Distributor cap had water and corrosion in it. Replaced Dist cap, rotor, and ICM. (When I replaced the dist cap, I scored a line across the dist & the block so I lined it up EXACTLY to where it was. ) Then it started up and runs. However, after that is when it is not running right. Also all this trial & tribulation occurred over a few months so the truck more or less sat the entire time. I have replaced the following: • Distributor Cap & Rotor • Plug wires & plugs • ICM • BOTH Carb Solenoids • Fuel Pump • Fuel Filter • Air Filter • Some (not all) Vacuum Lines I have cleaned the carb (but did not replace any carb bits, such as diaphragms.. They are not cracked) I have adjusted the Fuel Mix screw.. It seems to run best around 3-3.5 turns out. I have run Non-Ethanol gas I have run the fuel line into a clear bottle to see flow and it is flowing fast & freely. I have tested the issue by running gas from a bottle directly into carb (purpose of bypassing fuel system).. issue persisted. I tried replacing the Thermovalve (Ported Vacuum Switch) and broke the new one while installing it today. Just ordered another. But I doubt that's the issue, at this point I am just throwing parts at it and praying. LOSING MY MIND. WHAT ELSE IS THERE. It was running amazingly before the initial problem with the distributor. I can upload a video if it is helpful to anyone interested
This is the exact issue I have with my 98 HA4 (just picked it up) "surges & stall when cold, runs alright once warm" I however haven't replaced anything yet so was planning on doing the solenoids but interested in what the outcome of this is for you.
Hopefully someone has insight for us and chimes in. I think next I'm going to replace all the vacuum lines. It's gotta be that and/or choke related. I need to remove the air intake boot and physically watch the choke butterfly and see what it's doing. Also I bought a new ignition coil. Going to install that after doing the vac lines. Like I said, I'm at the point where I'm just throwing parts at it. Who knows maybe its got weak spark when cold. This sucks.
