4.0 OHV rough starts and vibrating idle

[Nonstopmaximum]

I have a headscratcher problem my 94 Ranger starts fine with first drive of the day but if I'm away for about 15-30 minutes and try starting it again it will struggle to start unless I give it gas or keep key turned for a few seconds. It vibrates every 2-3 seconds with idle at 600-700 RPM in drive or reverse, slightly less in park. Replaced IAC and that made idle vibration way less severe, MAF cleaning did nothing, no vacuum leaks, everything fuel related except injectors themselves have been replaced. Injectors are my prime suspect right now but I think I'll try spark plug and/or coil pack replacement first. I'd like to hear what everybody thinks before I continue there.

 

[franklin2]

Replacing the IAC improved it, did you also clean out around the throttle body and the IAC passages? All that brown gummy stuff?

 

[SenorNoob]

So warm restarts are a problem? If so, I'd suspect cracked head or bad gasket. The coolant in a cylinder causes a misfire only after it's been up to temp and started to cool down.

 

[Nonstopmaximum]

Got rid as much grime in the throttle body I can get I noticed there's a lot inside the upper intake manifold. No cracked cylinders boroscoped them and they're good and I'm not losing coolant. Putting Seafoam in the tank has sometimes gotten rid of the rough starts for a few days but they come back. I'll bite the bullet on coil pack and new spark plugs and see if that improves anything.

 

[JJMaine]

So warm restarts are a problem? If so, I'd suspect cracked head or bad gasket. The coolant in a cylinder causes a misfire only after it's been up to temp and started to cool down.

I can attest.🫩

 

[Nonstopmaximum]

I'm not sure my Ranger starts normally if it's been recently refilled or fuel cleaner is in the tank even when it's warmed up so I would think it's fuel or spark plug related.

 

[SenorNoob]

The only way I can see recently filled up having anything to do with it is if there is a hole in the fuel line in the tank or something to do with the charcoal canister.

 

[Nonstopmaximum]

No fix for the hard starts at warm yet but I got rid of the vibrating idle by tightening the throttle body idle screw so now it's in the 900 RPM range in park and around 750 RPM in drive. Before that anything below 700 brought on the vibration. I replaced all the spark plugs in my Ranger with Motorcraft ones and performance is a little better but not a huge difference and did nothing about the vibration. I think there could be something wrong with my fuel pressure I know my last mechanic botched the fuel filler neck before they didn't screw the thing in when I picked it up and took it to a gas station the neck was dangling somewhere under the bed. What it does now at some gas pumps is if I try to refill it and keep holding the pump handle down all the way for several seconds it overfills and spills gas.