90 F150 warm idle and hot start issues
 

I've been having a high idle issue with my truck after driving for 20-30 minutes. If I push in the clutch in, the idle will jump up in between 1200-2000 rpm. If I tap the gas it'll drop back down to 700-750ish but as soon as I take off or start letting the clutch out it jumps back up. It'll also run in gear at about 1500 rpm with my foot off the gas.

The hot start issue is that the truck won't start up again after driving for 30+ minutes unless I let it cool off again. If I give it throttle it sounds like it runs on half the cylinders and putters out when I let off the gas. Other than these two issues it runs like a champ.

The high idle could be throttle position sensor, vacuum leak(s), IAC system, even a binding throttle body or sticking EGR valve issue. . Those would need further diagnosing before any parts are replaced. Those are not temperature sensitive and I doubt they are causing a no start issue. . I believe the hot start problem is another issue. Being a hot start issue, I would determine if you are losing spark or have a fuel pressure issue. You would have to diagnose when the engine fails to start. Fuel trims might give some direction indicating a rich or lean problem.

I don't think it's a vacuum leak because it only does it when it's hot and I'm stuck in stop and go traffic. If the truck the engine isn't hot it runs just fine. As far as the hot start, I'm gonna throw a timing light on it and see if it's right. Then I'll check the coil and fuel pressure.

It's not timing. I wouldn't mess with it.

There is a possibility of a poor ground connection to the engine that depressing the clutch makes a better connection.

Might be a good idea to check all the grounds you can see that connect the sheet metal to any ground. If you start at the negative battery post and clean each ground connection, you might hit the questionable one. A good electrical tech can pin point this problem with voltage drop testing..

Ground connections are usually behind the kick panels, engine block, fender and on the firewall within the engine compartment.. Not near the clutch pedal and its mechanism. My bet is something sticking with the accelerator linkages or air is being introduced to the mixture. Yes, vacuum leaks can be temperature sensitive depending on where its leaking.An EGR valve which is stuck wide open may not allow the engine to restart.

Keep in mind when the clutch pedal is depressed it moves a lot of metal that is connected to the engine and sheet metal..