4.3l Engine Idle troubleshooting

YJJPWrangler

YJJPWrangler

Well-Known Member
Joined
Jul 19, 2005
Location
Charlotte
1992(ish) 4.3L TBI in the Willys.

Symptoms: High Idle. It typically idles around 1500rpm. The warmer it gets outside, the higher it goes. If I blip the throttle, the rpm comes down to around 900-1000 for a few seconds and then shoots right back up. I've been chasing this thing for a while now. I found that my TPS sensor was reading higher than normal voltage. Normal voltage at closed throttle(idle) is supposed to be between .45 and .55 volts, I was around .85. I was able to manually adjust the TPS down to .48. I also replaced the IAC and did the ECM reset where you jumper the A and B pin. Still no change.

Right now it will idle around 1600-1700 rpm, pedal response is flat. It won't rev past 3k and I'm getting some backfiring. It will also just randomly die, continues to drop idle until it kills itself.

Ideas?
 
I struggled with high idle on that motor with the same conditions. I chased it also and then learned to live with it. When I built my current 4.3, it idles high at times but I'm used to it now I guess. I thought it was something with my ECM or sensors, or...? I replaced everything for one reason or another throughout the process.
BUT it would rev to the moon. Backfiring and dieing isn't good. (That was never an issue with me). I'm wondering what the condition of the distributor is?
The S10 groups on FB is a pretty good resource, I've been using them for help with Sweenz which also has a problematic 4.3
 
@R Q , I think it's the IAC reset. Before I went into the TPS/IAC, it would rev fine, no backfire etc. Once I changed those out, that's when the problems started. I'm going to pull the IAC back out, clean it and the TBI thoroughly and redo the reset. I've also thought about smoke testing it to see if there are any major vacuum leaks.
 
Pulled the IAC out again, cleaned everything well. Did the reset procedure. Pulled a chunk of crud out of one of the TBI's orifice. Confirmed that the IAC passage into the TBI is clear. Still no change. Motor stumbles hard. When it does idle, its around 1500rpm but it quickly dies. Now won't rev past 2500.

It smells very rich. Injector spray is in a cone but it is not a mist.


Prior to this work, the jeep ran fine, although it idled high. The ONLY thing I did was TPS reset and put on a new starter. I measured the TPS voltage again yesterday and it is at .50 nominal voltage at rest. Specs are between .45 and .55. I didn't touch distributor/timing.

What I think is happening: IAC is fully closed and is not actuating. Still need to physically verify the plunger moves in/out. I think the IAC plus the TPS is causing it to run in a rich position.

Thoughts?
 
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