btw...jstluise...is that second hose, the back one on the bottom, also a coolant hose? when you pulled off the iacv, did it contain fluid, or is it an air hose?

thanks

 

I would be surprised if your IACV was bad. Sounds like you found your problem (coolant flow).

 

Hope so!! I appreciate your help. I just hope that back hose isn't plugged.

I also hope anyone else who deals with IACV's checks the front hose. It is fairly easy to remove and could be plugged easily due to its shape(s).

I'll post back in a few days with a follow up.

 

The saga continues. The latest little test I tried was completely disconnecting the coolant temperature sending unit just to see what happened. It ran fine and when I first started driving it I noticed right away that the idle wasn't undershooting like before when I let off the gas. The idle was a little higher because I'm guessing the ECU was in some sort of safe mode (CEL was on), but when letting off the throttle the RPMs would drop and stop exactly at 950ish and stay there...no hunting or moving around. I thought I was on to something, but a bit later in the drive I noticed the RPMs undershooting again like before...

Figured what the heck and replaced the coolant temperature sending unit ($17) even though my other one tested fine. I drove it today and didn't notice any improvement, so I'll probably return the sending unit. The RPMs still undershoot and my idle point is never consistent (sometimes it is at 750, other times 850-900).

The last two things I have not touched yet are the EGR system and the O2 sensor. Since my idle point changes regularly throughout a drive, maybe my EGR valve isn't fully closing (or closing sometimes, but not others)? I'm not sure what RPM the EGR valve starts to open...does anyone know? I've read about people deleting the EGR valve...that might be a good test for me to do, just to eliminate it as a possible problem. Or at least take off the EGR valve and see what it looks like.

I know this thread is getting long, but just to summarize here is what I've done:
-Replace cap/rotor/plugs/wires and set timing (routine maintenance)
-Cleaned & recharged K&N air filter
-New AFM (old AFM was out of spec)
-Cleaned TB and made sure all ports were clear, including idle screw
-Confirmed IACV is operating correctly
-Inspected TPS (passed)
-Inspected coolant sending unit (passed), but also replaced
-Inspected dashpot system (passed)

 

That sounds like what happened when I turned my idle speed screw all the way in. I finally found two vacuum leaks by spraying carb cleaner in different areas. From now on I'm only looking for vacuum leaks with carb cleaner, starter fluid, or by blowing smoke/fog into it.
I haven't fixed them yet so I don't know if it will 100% fix my idle issue.

 

I've been told to make sure the engine isn't warm when doing the carb cleaner vacuum check as it can catch fire. Is this a safe thing to do when the engine is fairly cool? I wanted to try it, but didn't. Wouldn't have helped me as my issue was a blocked coolant line into the IACV, but it would've been my first test before all others.


My truck seems to be running well, but I still need to fine tune my cold start idle a bit. I have no tack, so will have to get a meter.

 

You should check it when the engine is warmed up but yes there is the possibility of fire when using carb cleaner, starter fluid etc. That's why using an unlit propane torch is widely suggested. You can't get it into tight spaces as easily though.

Maybe you should do the poor-boy smoke test. You'll want to put a rubber glove or something of the sort on the end of the throttle body before you begin to help contain the smoke. I'd also try to do it using two people so one is free to look for areas of escaping smoke.

 

That guy in the video is sure a character lol

Lately, I blocked off the EGR completely to see if it had anything to do with my problem. Just undid the pipe going into the upper plenum and slid a piece of aluminum can in between before tightening back down. Drove it and didn't notice any improvement.

Right now I'm just to the point where I am going to leave it alone and drive it how it is. As long as I have my idle set at 850-900, the undershooting isn't that bad (I tried moving it down to 750 where it should be and it was pretty annoying). I haven't noticed any surging lately so I guess I'll just deal with it.

I wonder if my problem is somehow mechanical related, but I don't know exactly what that would be.

 

Dang, I was really hoping you would find it. If would be nice to see more posts like this ended with the fix. You gave it a dang good effort though.

 

I have a 1994 22re 4x4. The idle would surge up and down at a stop. Drove ok once going. I cleaned the throttle body and chamber . The carbon build up was bad. Cleaned the ports where the vacuum line are connected. The throttle body idle screw , pulled that out also and was full of carbon. Replaced the Oring on the screw. I couldn’t find one anywhere, so I found a Oring kit at harbor freight for $7.00 . Had over 300 Orings ,18 of each size. I put the 010 size on the screw and fit perfectly. ( Metric ) Started and warmed up my Engine, adjusted the screw to just under 1000 RPMs at idle. Runs like a new truck. Plus it had better power and less pinging, almost none at 3000 RPMs while driving. I’ve had no problems with the idle since.

 

From what I understand, if the idle is too high, I think above 1000, but it might be slightly higher, when you apply the brakes, the ECU cuts the fuel pressure down. After all, you don't need the engine running anywhere above idle when you're braking. SO, if the idle is above 1000, the ECU cuts the fuel down, or off, until the engine drops below 1000, then lets the fuel flow again, but it rises above 1000, so the ECU cuts the fuel, rinse repeat. Thus, the engine surging when the brakes are applied.

I believe the idle is supposed to be 850. It should be set to that before adjusting the timing as well, so the ECU doesn't interfere in the timing incorrectly.

Please don't misunderstand, all the other cleaning/repairing you did is great, no question, and definately essential. Especially the vacuum ports and the idle screw repair. But the engine surging when braking was just because the idle was a bit too high. IF the idle was too high because the idle screw had a bad o-ring, and was letting too much air past, replacing the o-ring and cleaning out all the crud in the air passage is absolutely the right thing. However, once it's cleaned and repaired, setting the idle too high will get the same surging when braking. Something to be aware of.

A note, BTW: If you spread a very thin coating of Vaseline onto the rubber o-ring when you install it, it will seal better, and last a fair length of time. Longer than the o-ring "naked", so to speak. Just something to think about. As long as it doesn't come into contact with gasoline, it won't interfere with the way the engine functions, either. Vaseline is a good thing for rubber. I use it on a lot of things. Heck, I spread a layer onto my door, and window, rubber every fall. It keeps the doors from freezing shut in cold weather. Easier to open by far. Windows, too, and helps the rubbers seal up better. Keeps the rain out. I graphite up the locks, and the key lock on the steering column, too. Again, keeps them from freezing up.

Good fortune to you!
Pat☺

 

Yea the ECU cutoff is iirc 1100 rpm when the brake is applied and the idle circuit is closed. There is a secondary cut out at around 2100 when the IDL is closed.

I actually thought about this on the way home tonight and I'm not clear if it's ignition, fuel, or.both that get cut...

 

I just checked THE BOOK (FSM). It said 1) The correct idle speed is 800, and 2) The ECU cuts the injectors off when the engine speed is above 1100 RPM. It says to run the engine up to 2500, then drop it back to idle, or press the brake pedal to activate the brake light, and you should either hear the injectors stop operating if you're using a sound scope on them, or feel them, stop operating momentarily, until the engine is back to idle. Then you should hear/feel them return to normal operation.

I hope this is some help...
Pat☺