My 1994 Ranger was having idle issues, idling real high after AC replaced. I replaced the TPS sensor, and it's been fine for about a week. Then today, Started ok, went to the store and when I started it to leave, it's racing again. I got almost home and shut it off and started it again, it's worse. I was just watching a video about changing the ECM and there was mention of the idle air control valve. Could this be my problem? When they did the AC, the snorkel was split so he just taped it. If I unplug the TPS, it idles fine with the check engine light on. Will this hurt anything? Thanks.

 

a) Sounds like it could be a vacuum leak. Big defffo on careful inspection of the taped repair and rest of the 'air tubes'.
Do that first.

b) With an engine idling, unplugging the IAC should cause stumbling / near stalling.
If the rpm stays the same / increases, you have a leak.

c) Just watching an ECM replacement video? You're not considering changing your ECM, are you?

 

No, I was just watching the video to see where it is. Yes, it does sound like a vacuum leak. I went out and started it a little while ago and it was fine. Something is changing. The air ducts are all bad, cracked an falling apart in places. Before the AC was replaced, it ran fin with all the cracks and all. There is no vacuum in for 4" ducts, just air flow to and from the air filter. You say unplugging the IAC, what's the IAC? I said unplugging the Throttle Position Sensor it will idle fine. I'm in Florida, it seldom gets cold enough to require a warm up period at high idle. Something got damaged or changed when the repaired the AC. When I replaced the Throttle Position Sensor, all was good for about a week, and now it's acting up again.

 

" I was just watching a video about changing the ECM and there was mention of the idle air control valve. Could this be my problem?" << There it is.
Unplugging the IAC (I assume the '94 trucks have one since it was in the video) checks if it's working.

 

Before I started it earlier, I unplugged it and plugged it back in. The idle started high but went right back down. If I unplug it when it's running, what should happen?

 

I started it up, idled fine. I disconnected the IAC, didn't make any difference. I went to take it off, the bottom bolt wasn't tight, it wasn't real loose, but it wasn't tight. I just tightened it down, I'll see what it does in the morning. Thanks.

 

I went and disconnected the IAC when it was idling nicely, no difference. I went to remove it, the bottom bolt was loose. I tightened everything up and I'll see what happens tomorrow. Thanks.

 

With unplugging, the rpms are supposed to drop to 500, or so. I believe 'no change' is not good and means a bad valve.

 

The idle was already low, so I'm not sure if it was supposed to change or not. I'll see in a while if tightening the bolt helped.