Idle Stumble + Lower Idle when turning off AC (1 Viewer)

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Hey, y'all

Just got a 94 and trying to figure out this low idle situation I got goin' on here. When I start the truck, it stumbles (it's stalled once going slowly in reverse). I noticed that it idles around 400rpm and when I turn off the AC, it goes down to around 350rpm. This seems a little unusual, but when I start driving for a little while and stop at a traffic light, the low idle seems to go away.

Any of y'all have any thoughts/advice/wisdom?


 
Have you checked tightness of throttle cable? Can result in high or low idle if adjusted improperly.
 
Have you checked the fsm? I had to adjust mine and get it back to spec 700-800 iirc? You can also use some type of lubricant. Spray on one end and hold up high so it runs the length. I had to replace mine the jacket was gone and all rusty.
 
Have you checked tightness of throttle cable? Can result in high or low idle if adjusted improperly.

The throttle cable does feel very easy to pull from the engine bay, but I've driven other 80's and the cable feels similar? I can double check and maybe tighten it to reach ~650rpm. But does that still address the issue with the AC affecting the idle?
 
Have you checked the fsm? I had to adjust mine and get it back to spec 700-800 iirc? You can also use some type of lubricant. Spray on one end and hold up high so it runs the length. I had to replace mine the jacket was gone and all rusty.

I've tried searching, but it might take me a few days because that boy is beefy to sift through.

And would you be able to clarify getting yours adjusted? Are you referring to the throttle cable?
 
The throttle cable does feel very easy to pull from the engine bay, but I've driven other 80's and the cable feels similar? I can double check and maybe tighten it to reach ~650rpm. But does that still address the issue with the AC affecting the idle?

The A/C will affect your idle. The additional load from the compressor causes the idle to go up a little. Perfectly normal. Dropping as low as you are is not.

Use some cable lube if the cable feels notchy. You want to tighten it until it's firm and your idle sits right at 600-700 with no A/C on.

Might want to clean or replace your IAC and check your intake for cracks/leaks. Also a few posts in the past on poor idle related to crappy O2 sensors.
 
^^^^^^THIS^^^^^
Idle speed is set by the ECU pushing the ISC valve, not the throttle cable.
Tightening the throttle cable to raise idle is the EXACT WRONG thing to do. You have other issues to address.
 
Check the intake tube from the air cleaner for cracks on the underside. Cracks allow unmetered air to enter the engine impacting the idle RPM.

I'll check the ISC valve to see if the connections are clean -- and then I'll check the vacuum lines, as well as the intake tube. Will keep y'all posted in the next few days!

Edit: Do you think the intake tube would affect the low idle going away once the engine is warmed up??
 
^^^^^^THIS^^^^^
Idle speed is set by the ECU pushing the ISC valve, not the throttle cable.
Tightening the throttle cable to raise idle is the EXACT WRONG thing to do. You have other issues to address.

On mine, my incorrect idle speed was due to the throttle cable. I had no other issues however.

I also said check intake for leaks, check IAC and make sure throttle cable was adjusted correctly. Not "tighten your throttle cable until your idle goes up to mask other issues, problem solved".
 
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Hey, y'all

Just got a 94 and trying to figure out this low idle situation I got goin' on here. When I start the truck, it stumbles (it's stalled once going slowly in reverse). I noticed that it idles around 400rpm and when I turn off the AC, it goes down to around 350rpm. This seems a little unusual, but when I start driving for a little while and stop at a traffic light, the low idle seems to go away.

Any of y'all have any thoughts/advice/wisdom?



I had a similar issue and cleaning the throttle body helped out a lot.
 
Cleaned the throttle body and the mechanic replaced a failed EGR vacuum modulator. The idle is not "gurgling" as much, but still has low idle. Idles around 400rpm now when AC is not turned on, which is better than before. But still idles low. What the frick! Trying to chase this down.

Intake tube doesn't look like it has cracks -- maybe I should replace the vacuum hoses?
 
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Idle still hasn't really been fixed with cleaning and EGR vacuum modulator replaced. Trying to find a new IAC valve. Been scouring the internet, but haven't been able to find it -- Toyota and Partsouq are all unavailable. Maybe another vendor?

Part No.: 22270-66010
 
You know that the IAC works because your idle goes up with the AC on.

Remove and clean your intake manifold. The various internal passages get clogged with carbon. Soak the whole thing in Simple Green for a few hours and push guitar string through the passages. Replace every vacuum hose and maybe the EGR solenoid while you're under there.

Also, make sure that all of the throttle body passages around the IAC are clean. To some people, cleaning the throttle body just means the main passage.
 
Thanks for the insight! I did clean the IAC, it wasn't that dirty, which got me thinking that it may be malfunctioning. But I'll maybe just take apart the intake and go piece by piece. Should be a fun weekend job. I know there exists a post out there, but is there a list of vacuum hoses, location and part numbers?? Might as well try and get all that done at once.
 

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