High idle acts like it is losing power

Hi and thanks for using 2CarPros.com.

This could be the result of many things. First, I need you to read through this link to see if there is anything that you find helpful.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

I would like start by checking for an engine vacuum leak. Here are the directions:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

You will need a vacuum gauge, but most parts stores will lend you one.

If there is no issue with engine vacuum, I recommend checking fuel pump pressure and pressure regulator. Here is a link with general directions:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Here are directions specific to your vehicle for checking fuel pump pressure. The attached pictures correlate with these directions. Additionally, based on your findings, there is a list of possible causes at the end which describe what can be causing readings which are not within the manufacturer's specifications.

2. CHECK FUEL PRESSURE
(a)Check the battery voltage above 12 volts.
(b)Disconnect the cable from the negative terminal of the battery.
(c)Disconnect the wiring connector from the cold start injector.
(d)Put a suitable container or shop towel under rear end of the delivery pipe.
(e)Slowly loosen the union bolt of the cold start injector hose and remove the bolt and two gaskets from the delivery pipe.
(f)Drain the fuel from the delivery pipe
(g)Install a gasket, SST, another gasket and union bolt to the delivery pipe as shown in the figure.
ST 09268-45012
(h)Wipe off any splattered gasoline.
(i)Reconnect the battery cable.
(j)Short terminals Fp and +B of the check connector with a wire.
(k)Turn on the ignition switch.
(l)Measure the fuel pressure.

Fuel pressure:
22R-E 2.7 - 3.1 kg/cm2 (38 - 44 psi, 265-3O4 kPa)
22R-TE 2.3 - 2.7 kg/cm2 (33 - 38 psi, 226 - 265 kPa)

If high, replace the pressure regulator.
If low, check the following parts.
Fuel hoses and connection
Fuel pump
Fuel filter
Pressure regulator

(m)Remove the service wire from the check connector.
(n)Start the engine.
(o)Disconnect the vacuum sensing hose from the pressure regulator and plug it off.
(p)Measure the fuel pressure at idling.

Fuel Pressure:
22R-E 2.7 - 3.1 kg/cm2 (38 - 44 psi, 265 - 304 kPa)
22R-TE 2.3 - 2.7 kg/cm2 (33 - 38 psi, 226 - 265 kPa)

(q)Reconnect the vacuum sensing hose to the pressure regulator.
(r)Measure the fuel pressure at idling.

Fuel pressure:
22R-E 2.3 - 2.6 kg/cm2 (33 - 37 psi, 226 - 265 kPa)
22R-TE 1.9 - 2.2 kg/cm2 (27 - 31 psi, 186 - 216 kPa)

If no pressure, check the vacuum sensing hose and pressure regulator.

(5)Stop the engine. Check that the fuel pressure remains above 1.5 kg/cm2 (21 psi, 147 kPa) for 5 minutes after the engine is turned off.
If not within specification, check the fuel pump, pressure regulator and/or injectors.
(t)After checking fuel pressure, disconnect the battery ground strap and carefully remove the SST to prevent gasoline from splashing.
(u)Using new gaskets, reconnect the cold start injector hose to the delivery pipe.
(v)Connect the wiring connector to the cold start injector.
(w)Check for fuel leakage.

I hope this helps. Let me know what you find and if you have other questions.

Take care,
Joe