Back in my 80's highschool shop class they had us setting mixture screws with the sniffer, so I do understand that. It seemed pretty stupid to me and my stuff was treated to a little richer mixtures setting them by a combination of feel/sound and or tachometer readings. Eventually I started tuning idle by vacuum readings.

 

I tested my IACV out again but this time in a precisely controlled temperature chamber we have at work. I put it in at 0°C (32F) and 90°C (194F) to see the change. As seen from the pictures, at valve fully closes at the high temp, so I would say it is working pretty well.



I pulled the TB off again today and double checked the TPS. Everything was good. I put my IACV back on as well.

I haven't taken it for a drive, yet, but the initial startup in the driveway seemed pretty good. A nice high cold idle (1500) that settled down as the IACV warmed up. It was idling around 850 and I wasn't getting any surging or stalling after letting off the throttle. We'll see how it goes after driving it for a bit.

 

Quick report on mine, I finally checked my TPS.
I checked it while the engine was stone cold. Every reading was within spec but when I opened it up from closed throttle to WOT with VTA & E2 connected it had a dead spot around 3/4 throttle, guess I need a new one. I also tried disconnecting it when the engine was warmed up and running. It responded by gaining rpm.

I don't think it'll solve all my problems though. It's kinda acting like it has a vacuum leak after it's fully warmed up. I tried finding leaks with a propane torch but didn't get any response out of the engine that I noticed. I'm starting to wonder about the PCV valve/gasket/hose.

If I snap the throttle open revving the engine the rpm's come back down but it'll start climbing again after several seconds.

 

After driving it for a few days it seems to be a bit better, but not all the way back to normal. Every once in a while I'll see the idle dip after letting off the throttle (e.g. letting off the throttle the idle might drop down to ~600 RPM before coming up to normal idle). This is not normal for sure.

I did notice one time some surging like before while idling, but never happened again.

Another thing is that the idle speed is not consistent. Sometimes it idles around 850, other times it is down around 750. It does hold steady and doesn't hunt around, though.

Maybe my EGR valve is slow to close/getting stuck open when I come off the throttle? I can't think of anything that might be causing it. Maybe the O2 sensor? I guess I can test the EGR and O2 sensor next.

*Also, I think my idle is set a bit higher than before. I have a feeling that if I try to bring my idle down to 750 I will see more issues come back. As far as the mixture screw on the AFM, the times when the idle holds steady and runs fine makes me thing the mixture screw doesn't need to be messed with. Something else is causing the stalling/surging.

 

Well that sucks.

Keep hunting though, it would be nice to see a successful conclusion.

 

I've also had a terrible idle surge issue for the past several months. When cool, my truck ran great but, when warm, began surging badly when I touched the brake pedal. I checked the brake booster for a vacuum leak, but that was ok. I began by turning my idle screw as far in as possible, but that only slightly lessened the issue. After enough research to make me crazy, I then focused my attention on the idle air control valve and found (thru several posts) that removing the air chamber going into the throttle body and taping off the hole which goes to the iacv tests the valve. After doing this, replacing the air chamber, and resetting the idle, the truck runs and idles great again. I have tested it not only when warm, but after it cooled. I now know that I need to remove the throttle body and iacv and clean them to see if the valve can work again or has to be replaced. I bought another iacv just in case, but hope the old one might be junked up or can be cleaned enough to work. Since it is my only transportation, and I am not a wiz mechanically (I can do it, but would feel better if I could take as much time as necessary) I am a bit nervous about my next steps.

My question is this...can I run this thing for a few days or weeks with the valve closed off? It runs fine now, but I suppose it is there for a reason? I don't want to cause myself further problems.

Any advice and info is greatly appreciated!

 

To answer your main question: running without the IACV will not cause any problems. Its only function is to raise your idle when the engine is cold.

If I understand correctly, you taped off the port inside the throttle body that leads to the IACV. This essentially removed the IACV from the system (i.e. air can no longer bypass the throttle body and go into the upper plenum). There is no issues with running the truck like this, I did it for a while. About the only issue you might see if hard starting/idling when cold because the job of the IACV is to increase the idle when cold until it warms up.

As for the surging, if the IACV is the problem it is most likely not closing off all the way when warm. Either it is not getting warm enough (coolant flow problem) or the valve isn't shutting all the way (out of adjustment or just broken). When the IACV doesn't close all the way when warm, you will get a high idle and in turn the ECU will cut fuel, causing surging. Basically the ECU sees a warm engine and high idle, but a throttle that is still at idle, so it cuts fuel to bring the idle down. It would help if you elaborate on what is exactly happening when it is "surging" for you.

As far as the surging being caused by your brake pedal. I've read a little bit about that, but not enough to know for sure. I know the ECU receives a signal from the brake circuit and when the brake is applied the ECU will cut fuel, which can cause surging. Someone with more knowledge on that might chime in.

 

I appreciate the reply. I feel better knowing I can drive the truck for a bit if necessary.

My "surge" was only when warm, and when the brake was applied. (started and ran great when cool) When I removed my foot from the brake it stopping the rapidly rising and lowering it was doing, (not sure what rpm was involved because my truck has no tach) but the idle was still too high. Since I'd already lowered my idle as far as possible via the idle screw, it felt like a vacuum leak.

I believe your explanation of the brake involvement is correct as far as cutting the fuel, and I will be interested in knowing why the valve isn't closing. The truck has only 60k original miles, and there isn't a big carbon build up in anything. I must say though...when I checked the hose lines going into the valve and out of the valve, with the engine warm, they were not hot. not really even warm, which makes me wonder about how much coolant is even flowing thru it? I had the "valve" located behind the thermostat pulled and it was clean as a whistle, so no plug up there.

Whenever I pull the TB off, I will dunk the IACV in hot water and see if it closes. If not, I will put the new one on.

As for now, the engine cranks ok, but I need to give just a bit more gas than normal. All else is good.

Thanks again for the reply!

 

Yes, it sounds like your IACV isn't closing enough or at all, so you are getting a high idle regardless of engine temp. Then, your ECU sees a high idle, no throttle, and the brake being applied so it cuts fuel.

If the coolant bypass hoses to the IACV weren't warm, then I would be looking at possible coolant flow problem. Drain your coolant and pull the TB and the IACV. You can blow air through all the coolant lines and see if they are free flowing or not.

While you have the TB off, you can make sure all the vacuum ports are clean and free flowing...use intake cleaner. Also remove your idle adjustment screw (mine was pretty gummed up) and clean it...check the o-ring on it as well. Be careful with getting any cleaner on your TPS. While you have everything off, double-check your TPS using the guide that was posted in this thread. Might as well since it is easier with the TB off.

With the IACV disabled right now, are you able to bring the idle down with the idle adjustment screw? Or is it still bottoming out with a high idle?

 

OK, will do. Already removed the idle screw early on in the process and it was clean and the O-ring was good. Went ahead and added plumbers tape to make sure there is no leak. I have been, and am still, controlling the idle completely with the idle screw. In my case, I actually had to increase my idle once I blocked of the IACV. It was too low to crank with the valve out of the picture. I had it so low because the idle increased too much when warm. Right now, it is great. It really seems like this is what has been the issue.

Just had my coolant replaced and the system flushed a while back, but it was really junky, so could still be a blockage, I guess. It was very rusty. I hope it looks like hell when I take it off, and then cleans up like a new one! We shall see.

I think I will clean the MAF while I am at it. Did you check that out on yours?

 

Depending on how your coolant looks coming out, it might be worth flushing it again. As long as its not freezing outside, I usually just fill back up with distilled water and run it for a while, drain and repeat with distilled water. Once it is coming out looking good, then fill with coolant.

There isn't much to clean on the AFM (aka MAF), ours is just an airflow flap and a temp sensor, nothing fancy. Right now I am running a replacement AFM because my original one failed the tests. Was hoping that was my problem but it is not looking that way.

 

Can anyone tell me what the large, black screw is in the photo and what it does? Might as well learn all I can while I'm at it. I assume the hoses coming out are air hoses and not coolant?

 

Hmm, I'm not sure...that port on my plenum is plugged off. Definitely air, not coolant. Follow the hoses, where do they go? Maybe something to do with the A/C? (I don't have A/C)

What year is your motor?

 

That's either an A/C or P/S idle speed adjuster, can't remember which one.

 

It must be the A/C idle speed adjuster. The P/S idle speed adjuster is the next port forward...at least on mine it is.

 

Thanks guys. I've no idea for sure. I do have a/c, so could be that, but not sure why the screw? Anyway, my truck is a 92, 22re, 4cyl, 5 speed, 4wd. original owner (me) with 60k.

Sooooo, today I made a big discovery. Since I've been afraid to just pull off the tb, I keep making a step each day more than the day before. Today, I had taped off the iacv, but was worried about it, and when I checked the tape was beginning to come off. So, I decided to pull off the hose on the front bottom of the iacv, which is a coolant hose. I did so because it has not been hot even when the engine is. As I suspected, it was COMPLETELY blocked with rust. the hose is so oddly shaped with so many elbows that it can easily get plugged. Truth is, no coolant has been getting into my iacv!

After completely removing the hose and running a flexible but strong piece of coated wire, I was able to get water moving freely through it again. Before reinstalling, I unplugged the iacv port it was connected to, as well as the upper port it came from. I then ran water under pressure through the top port (the one behind the thermostat that often gets plugged) and the water flowed freely out the iacv

I took it for a long enough drive to know the valve must be working again, although it may need to be removed and cleaned better. I've no tach, so I adjusted the idle speed by ear, and it seems to running very good again. Hopefully it will continue.

I also sprayed and cleaned the tb as much as possible. It was dirtier than I thought it would be. If it continues to work, I will still want to take the tb and iacv off and clean them really good.


Wish me luck!

 

Looks like you are on your way to getting it back to normal...now when you are done with that come over and fix my truck!

Pretty sure that is what it is. The screw is for adjusting the idle when the A/C is engaged. The screw adjusts how much air is bypassed. Basically you just have to turn the A/C on and then use the screw to dial in the correct idle as specified by the FSM.

 

Good one! This whole ordeal has about driven me mad! I need a week in the islands with a swimsuit model to recover! Or for any reason actually....

Truth is, all these issues are trial and error. I still need to clean out the other IACV hose, but it is so hard to get to unless the TB is removed. I hope it isn't plugged also. For now, I am optimistic!

 

Biggest challenge of getting the TB is breaking those coolant hoses free since they have been on there for so long, but once that is done it comes on and off pretty easily. Might want to grab a new TB gasket. It is worth doing so you can check your TPS and clean out any gunk.

Your IACV is built into the TB, isn't it? I don't know what year they switched from the separate to the integrated IACV.

 

already picked up a tb gasket as well as an iacv gasket. that one wasn't easy to find. as far as the hoses, they are tricky for sure. the one came off fairly easily today, but the back one seems difficult. one of the hardest parts is that those clamps seat deeply into them and it takes a long pair of pliers to reach them. I really need one of those 10-12" needle nose. I used regular needle nose and it was difficult.

my iacv is separate, but screws into the bottom of the tb. bought one for $120, but hope to take it back.