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Q: Engine hesitates when warm - 1997 Toyota Tercel

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I have replace the fuel pump, fuel injectors, fuel filter, fuel regulator, tps, idle control valve, map sensor, ignition coil and cables, etc. That car has no catalytic converter and no engine codes. One thing I have notice is that when is cold runs better than when it warms up(when cold I can the rpm up to 3,500 as when warm will only go as high as 2,500 rpm, and when cold will run up to 60-70 min as when warm will only go up to 55-60mph.Another thing I have noticed is than when I clean the throttle area and intake manifold the problem seem to get better. I have check for vacuum leaks and nothing. I'm guessing either a gasket is bad when it warms up or I have a leak somewhere that I can't find. Any ideas will be greatly appreciated

My car has 190000 miles.
My car has a manual transmission.

A: Hi there. As you already know, replacing co...

Hi there. As you already know, replacing components without diagnoses can be expensive and time consuming without resolution. A few things come to mind concerning the lack of performance. First, camshaft timing needs to be checked. When the engine is at TDC (top dead center) #1 cylinder on compression stroke, the camshaft timing marks need to be lined up.

Second, with the engine at operating temperature, the ignition timing needs to be set at the manufacturer’s specification. Once timing is checked and set, put a vacuum gauge to a manifold vacuum source and then you should see 17-22 inHg. Even though there is no catalytic converter, the exhaust system may still be partially restricted by a faulty muffler or resonator.

I recommend having a certified mechanic, such as one from YourMechanic, come to your location to determine why the vehicle is hesitating and showing a lack of power.

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