Hello,
I am new to the forum and am looking for some Ford guru help. I have a 1998 4.2l w/auto tranny that I can not figure out for the life of me. Engine was replaced with a used unit when the original locked up. Have not been able to get the used engine to act right. At first the only issue was that it would die intermittently at idle or when first put into gear. At this point it has to be driven for a while for it to die, but it has a slight miss when barely accelerating which will go away as more throttle is applied(always occurring). Also when I press the accelerator from a dead stop it boggs down for a split second then it will go fine(always occurring). Then, it will sometimes miss for a split second stopped at idle in gear, or it will just die. Always will restart immediately. Also, every now and then at around 2k rpms it will buck a few times and then go away.
What I have replaced: fuel pump and filter, maf sensor, iac valve, cmp synchronizer and sensor, crank sensor, coil pack, swapped t-body with old one, replaced all vacuum lines, plenum gasket with good thick one, bank 1 sensor 1 O2 sensor(threw a heater code), umm I think that's it.
I need help...bad
Thanks!

 

From your description it sounds like two issues are occurring.
First, the idle is not acting right.
Re check the IAC and TPS assembly. They are mechanically linked together.
Do a check of the IAC control with engine at idle. Remove the IAC plug and note if the idle drops. If yes it's working, if no it's an issue.
The TPS is linked to the throttle shaft and must signal the computer of the throttle angle to add fuel as needed plus the signal is used for other functions.
Second is the misfire:
Check fuel pressure.
Check for codes set.
Is the cam position sensor set in and 'timed' correctly for proper fuel injection timing.
.
A problem you could now have is so much has been done that a new issue might have been created.
It will take diagnostics to track down the issues one at a time before changing any more parts.
Basically you changed a lot part in hopes of being lucky. It's costly and not the way to go about repairs..
Good luck.

 

Yes it does change the idle when I unplug the iac. When I changed the cmp synchro I got the tools & did it right. Whats strange is no codes. Fuel pressure is good. Is there a way to test the tps?

 

Yes, two ways.
1. With key on, measure the voltage change from center lead to it's return side, 'not to ground', for smooth rising reading.
2. Measure resistance rise from the same terminals with the plug disconnected for smooth change..
.
Good luck.