I have a 1987 Toyota pick up. 22R carb, 2WD 4 spd.
342,000 miles. One owner. (me) I replaced the head at 300K. In the last few weeks the truck will run great until it warms up and then after a sustained speed drive of 10 mins or so at 55mph the truck will idle roughly.Also when accelerating from say 45-55mph the engine seems to hesitate and respond roughly until the new speed is reached. I replaced the EGR, checked the tubes for carbon build up, replaced the vacuum modulator and the BVSV. Ignition timing is spot on. Plug wires, fuel pump, fuel filter etc are all new, and compression is well within specs. Any ideas as to what is causing this? Any help would be most appreciated."
Interesting problem.
Have you checked for vauuum leaks and/or sticky valves with a vacuum gage?
Have you checked the vacuum solenoid that operates the EGR valve?
Have you checked the fuel pressure regulator? (although the erratic idle yet good highway cruising would tend to put that low on my guess list)
Have you checked the distributor for play in the shaft? For erratic vacuum in the vacuum advance (leaks)?
It the lever that operates the accelerator pump clean and free? These can get gummed up and sticky on these carbs.
I’ll keep cookin’ this one on the back burner, but that’s all I can think of at the moment.