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Toyota T100 starts rough when warm, now idles rough

For quite some time (years) my 1995 T100 (base model 4 cyl 2WD manual tranny) has started easily when cold but gets cantankerous when starting warm (or hot engine). The check engine light would intermittently come on and go out on a weekly to monthly basis, but has not come on in 3-4 months.

A friend has played around with the EGR valve, and the problem has gotten worse. Tonight, it was running a bit rough even after startup.

Have a new rotor/distributor cap, plugs & wires are relatively new, air cleaner is K&N and clean, vacuum hoses all seem good and well-connected, PCV valve is clean. Mileage is a bit lower but not drastically lower.

I’m thinking, just replace the EGR valve. But could it be something else? What could it be?

First clean your MAF sensor (if so equipped) and if that helps you should either ditch the K&N or at least get the oil level down. Over-oiled K&Ns notoriously create intake issues.

Nothing that you said has been done or inspected involved fuel supply. Put a fuel pressure gauge on it to investigate. Leave it on for a while to see what the pressure does on warm shut down. My first guesses about your actual problem involve either a bad check valve at the fuel pump (too little fuel on restart) or a leaking fuel pressure or injector (leaking fuel into the intake). How old is the fuel filter?

Without knowing either the error codes associated w/ the check engine light or what about the EGR was messed with it would be hard to comment. However, if your EGR were stuck open it could behave like this - it basically acts like a vacuum leak.

I think you have a fuel problem tho.

My friend/mechanic will be doing a fuel pressure test next.

He’s tried to clean the EGR valve with carb cleaner (yesterday) and it started & idled fine. Later, it began to idle roughly again and this morning it has varied from idling & running roughly to running & idling smoothly.

BTW - truck is gently approaching 200K miles; 198,500 & counting! See pic from Feb storm (before the 2nd 30")

Nice looking truck!