Tdc 411 & 412

[sprocketdog]

I have a 93 Ranger XLT 4x4 4.0L Auto Trans all stock except a Jet Performance Chip which did seem to help a little on mpg and maybe HP.

It's under powered I think and get barely 14 MPG.

I haven't had it long but the idle rpm has always been high I think 1200 warm

Anything I do like put it in park, drive, reverse, the rpm jumps up to the point I have to brake to keep it from leaving without me

I've had a tune up plugs, wires, filter etc. right after I bought it to try and stop all this.

I just bought a ford reader and did self tests, the KOEO gave 111 but the KOER gave 411 Cannot control RPM during KOER low RPM check.
and 412 Cannot control RPM during KOER high RPM check.

I have read until my eyes are bleeding trying to find out what might cause these.

One said to pull the plug on the IAC and that the rpm should change but it didn't, so I pulled it and did an OHM test which gave around 10 and did a low voltage bench test and proved the magnet did open the valve ports.
Put it back without magnet and hand slide the valve and it reved the rpm and would idle back to around 1100 +

Back together with that since to me, it's just a dash pot and working.

What would be some likely causes and fixes

Thanks

 

[dogfriend]

If your idle is too high, (and it is) then the first thing to look for is a vacuum leak. The IAC can't control the idle speed because there is too much air leaking in from somewhere else. Check all vacuum hoses and fittings for leaks.