I need help with a problem I'm having with my 92 E 250 4.9L . 304K miles. The idle is very rich ( bad enough to fail PA inspection) In addition when I put the van in reverse it stalls. This only seems to occur after its been running a few minutes. I check the TPS and IAC ,at least for freedom of movement, and they seem ok , anybody have any ideas?

 

Well, you can really test the TPS, IAC by just looking at it for physical damage. You need to use a multimeter to test it.

You could try removing the IAC and clean the carbon of it and clean the spot whre the IAC goes in the TB. IAC is usually around $29 and TPS is around $19. Both easy to replace.

What about your sparkplugs? spark plug wires? When was the last time they were replaced? BTW, check the spark plug wires for nicks as it might be rubbing on a metal surface.

 

I did measure the resistance on the IAC and found it to be 9 ohms across the terminals. I also tried running the van with it disconnected and found that it ran ok in park but seemed to idle down when I put it in drive. That tells me that is working at least to some degree or am I misreading it?