- Joined
- May 11, 2026
- Messages
- 1
- Points
- 1
- City
- Spanish Fort
- State - Country
- AL - USA
- Vehicle Year
- 1993
- Vehicle
- Ford Ranger
- Drive
- 2WD
- Engine
- 4.0 V6
I have a 1993 Ford Ranger XLT, 2WD, 4.0L OHV, Automatic Transmission with 190,000 miles. The truck had been sitting for about 5 years and the fuel system was shot.
I flushed the fuel system and replaced the fuel pump and filter, fuel regulator, spark plugs and wires with new parts. I cleaned and "rebuilt" 10 fuel injectors and used six with equal flow rates. Of course replaced both intake gaskets in the process. I replaced most of the vacuum lines and confirmed there are no leaks. The IAC was stuck, so I replaced it with new. The truck ran pretty good at this point, but I still have a rough idle. I have since replaced TPS, CKP, O2 sensor, and coil pack with new parts. I also replaced the ECM, MAF, and ICM with parts from a junkyard with no change in idle.
The rough idle starts about 30 seconds after startup as the idle settles down to around 600-700. When it warms up the idle is about 600 and the vibration is worse. When I step on the gas, there is little hesitation and the engine seems to run great at any speed above idle. If I disconnect the IAC when the engine is cold, the idle drops. When the engine is warm there is no noticeable change. I put an oscilloscope on the IAC and the voltage is pulsing from 2V to 8V at about a 50% duty cycle. Is this normal? I was expecting to see 0-12V pulses. If I snap the throttle open, the pulse width shortens to about a 10% duty cycle which is expected then returns to 50%. Also, If I hold the RPMs at around 3000, there is no change in the duty cycle. I would expect the IAC to remain closed at anything above idle. Both ECMs (original and junkyard) are doing this. Resistance on the white/blue wire between the IAC and ECM is 0.3 ohms. I jumper-ed the red wire on the IAC directly to bat+ and there was no change in the signal or idle. The red wire also reads about 0.3 ohms between the IAC and bat+. I cleaned and re-seated the salt and pepper connectors.
A couple of cylinders have compression of about 130 while the rest are at 160. A vacuum gauge shows a little jitter at idle indicating a valve issue. Could these mechanical issues be causing the rough idle yet still allow the engine to run fine at anything above idle? I soaked the piston in some Sea-Foam and added some to the oil in hopes of loosening any possible stuck rings. I will do another compression check after I change the oil in another 100 miles.
This free truck is getting expensive. Any ideas would be appreciated.
I flushed the fuel system and replaced the fuel pump and filter, fuel regulator, spark plugs and wires with new parts. I cleaned and "rebuilt" 10 fuel injectors and used six with equal flow rates. Of course replaced both intake gaskets in the process. I replaced most of the vacuum lines and confirmed there are no leaks. The IAC was stuck, so I replaced it with new. The truck ran pretty good at this point, but I still have a rough idle. I have since replaced TPS, CKP, O2 sensor, and coil pack with new parts. I also replaced the ECM, MAF, and ICM with parts from a junkyard with no change in idle.
The rough idle starts about 30 seconds after startup as the idle settles down to around 600-700. When it warms up the idle is about 600 and the vibration is worse. When I step on the gas, there is little hesitation and the engine seems to run great at any speed above idle. If I disconnect the IAC when the engine is cold, the idle drops. When the engine is warm there is no noticeable change. I put an oscilloscope on the IAC and the voltage is pulsing from 2V to 8V at about a 50% duty cycle. Is this normal? I was expecting to see 0-12V pulses. If I snap the throttle open, the pulse width shortens to about a 10% duty cycle which is expected then returns to 50%. Also, If I hold the RPMs at around 3000, there is no change in the duty cycle. I would expect the IAC to remain closed at anything above idle. Both ECMs (original and junkyard) are doing this. Resistance on the white/blue wire between the IAC and ECM is 0.3 ohms. I jumper-ed the red wire on the IAC directly to bat+ and there was no change in the signal or idle. The red wire also reads about 0.3 ohms between the IAC and bat+. I cleaned and re-seated the salt and pepper connectors.
A couple of cylinders have compression of about 130 while the rest are at 160. A vacuum gauge shows a little jitter at idle indicating a valve issue. Could these mechanical issues be causing the rough idle yet still allow the engine to run fine at anything above idle? I soaked the piston in some Sea-Foam and added some to the oil in hopes of loosening any possible stuck rings. I will do another compression check after I change the oil in another 100 miles.
This free truck is getting expensive. Any ideas would be appreciated.
