I have read many of the posts regarding others who are experiencing poor acceleration, stalling, and poor idling. I have checked some of what was suggested, but no luck. My 1985 4runner (EFI) runs great until 4-5 minutes into the ride and I start going up a steep road all of the sudden the 4runner starts hesitating in every gear and exhaust begins to cough (no smoke just sounds like it is struggling), but not backfire. Once the hesitation starts, it will continue even if going downhill until I get home. However, the vehicle always idles fine. I checked the following and in working order: vacuum hoses, spark plugs, changed dist. cap and rotor, ignition timing at 5 degrees advanced, cleaned throttle body, no air leaks between air filter and throttle body. Could it be a clogged catalytic converter causing excessive back pressure after it warms up? Looking for suggestions to narrow down the issue so I can spend more time off roading with the kids than working on the vehicle. Thanks

 

Have you ever changed the fuel filter ?, if not i would try that next.

 

I changed the fuel filter today and it still hesitates when it warms up. The 4Runner runs great when it is cold, but as soon as it gets to normal running temperature it hesitates. What would warm up with the engine and then cause hesitation if it was working improperly. All I can think of is a clogged catalytic converter causing excessive back pressure as it heats up. Maybe I am answering my own question, but looking for your suggestions.

 

I have not adjusted the valves since I bought it. What is a valve lash?