the warmer the truck gets, the worse the idle gets

[quote:838132e48c="danmad37"]Engine Performance problem
1993 Ford Explorer 6 cyl Four Wheel Drive Automatic 200000 miles

I have a 1993 Ford Explorer and the warmer the truck gets, the worse the idle gets. I have had a scan on it, and it read the mass air flow sensor was bad, so I replaced it, but no change. I have replaced plugs and wires, and still no change. The truck, however, seems to run fine while driving or accelerating. What could the problem(s) be? Thanks.[/quote:838132e48c]

Could be a problem with the throttle body. If it was ever cleaned, that may have caused the problem. The throttle body on these vehicles should NEVER be cleaned.

Also, look for air leaks in the intake system. All air entering the engine should go through the Mass Air Flow sensor. Look especially in the PCV line, vacuum line to the transmission, and intake manifold gaskets.

I had the intake manifold gaskets replaced and checked for leaks, but they said it was fine. Someone pointed me in the direction of the fuel pressure regulator. I can pull the vacuum line off of it, and it doesn't affect the idling of the truck, and someone told me that when you pull the vacuum line off of it, the motor should idle up. Could this be my problem? I was also told to check the EGR valve and ignition coil?

[quote:305d09bef6="danmad37"]I had the intake manifold gaskets replaced and checked for leaks, but they said it was fine. Someone pointed me in the direction of the fuel pressure regulator. I can pull the vacuum line off of it, and it doesn't affect the idling of the truck, and someone told me that when you pull the vacuum line off of it, the motor should idle up. Could this be my problem? I was also told to check the EGR valve and ignition coil?[/quote:305d09bef6]

The fuel pressure regulator should not have much effect on idling. With a fuel pressure gauge connected, removing the line should cause the pressure to rise to about 45-48 psi. This is the only way to test the function of the regulator. The idle may rise slightly because of the air entering the vacuum line.

If the ignition coil was causing a bad idle, it would be more pronounced under load. A bad spark at idle becomes a bigger problem under load.

EGR is a possibility. You can check this with the self-test. During self test, the PCM opens and closes the EGR to verify operation while monitoring the EGR backpressure sensor for correct readings.

The most sensitive part is the throttle body. This is designed to never need cleaning because the throttle plate is sealed when the throttle is closed, and idle air is directed through a calibrated hole in the plate to maintain a minimum idle speed. The PCM then operates the ISC valve to obtain the correct idle speed and to compensate for engine loads such as A/C, power steering, and transmission being in gear. A sticky ISC will give you a fluctuating idle as will a throttle body that has been cleaned.

I just went out there and sprayed some carb and choke cleaner around the vacuum lines and mass air flow sensor and the intake manifold, but never heard the motor bogg down to indicated a leaky line or gasket. What is a sticky ISC?

[quote:496542b22b="danmad37"]I just went out there and sprayed some carb and choke cleaner around the vacuum lines and mass air flow sensor and the intake manifold, but never heard the motor bogg down to indicated a leaky line or gasket. What is a sticky ISC?[/quote:496542b22b]

ISC is the Idle Speed Control motor. Lotated near the throttle body, and has a 2-wire connector plugged into it. This controls idle speed by bypassing air around the throttle plate. It is controlled by the computer. This can stick and cause idle quality problems.

I went out and sprayed some carb cleaner in the idle speed control valve your talking about and srayed some penatrating oil in it, but it is still idling really rough. What should I do now? Thank you.