JEBSR5

What is it with the 3slo idle? Maybe it's just me, but every vehicle I have ever owned that was fuel injected has had a rock solid idle once op temp was achieved.
My case, really no big deal, but I ask all you experienced people out there why is it I can set idle at rock solid 800 RPM and it stays there on 3 slo until I move the vehicle. Meaning from red light to red light the idle is never the same. It will vary from 600 to 900 RPM. Heck, sometimes it even goes a few lights at 800 RPM at rest or idle. Mine has always done this, so I figured normal for the 3 slo and no big deal, right. What's a few hundred RPM in the scheme of things?
My rig is in very good condition mechanically, engine wise anyway. Well maintained, clean intake and all the tune up maintenance.
Is it a crappy computer control involving the computer or is it crappy sensor or do all 3 slo's do this and I'm way off on calling it crappy. Like I said, it's done this for 200k miles. Obvious choice to me would be IAC valve, but since you would have to buy a whole new throttle body to test that out, obviously my money tree is stunted this year and won't be producing for awhile yet. Any thoughts, dare I say debate or arguments?

Chime in anyone.

I would like to put this mystery to rest, since I will be DD'ing this rig for some time.

Maybe I'm just , but I have searched and researched. Now it's time to rely on experience and wisdom.

Hey, good time for you MDT techs to chime in too. I'm about to with this for living for so long with it.

itsmeagain5789

when mynes warm, it will idle down to 300 rpm and try to cut off, i still havent figured out whats up with it. it started yesterday. but myne is pretty well tuned also.

rdharper

Disconnect the TPS connector (carefully), restart (you will throw a code which won't hurt anything). See if variable idling goes away. If so, the TPS is misadjusted or not working correctly, if no change in performance, reconnect the TPS... code will go away.

JEBSR5

Mine used to do that, but only when AC was on and it would kick up to 700 RPM or so and drop down again. Turned out the resistor block in front of radiator that routes power to AC fan was broke. After fixing that, all was well. Must have also fed some kick RPM up switch also. May not be your problem, but throwing that out there.

Maybe we can get some experienced comments in here and help us both out.

JEBSR5

Haven't tried that specifically and the reason is that I have adjusted TPS twice with same results. Toyo mechanics have been unable to resolve either, I'm sure this has no bearing on the problem and only pointing out if they don't know, what do I know compared to them?

I think I read somewhere that you can drive quite a ways with it disconnected with no harm, but just checking before I try it.

rdharper

In the case of the TPS you can disconnect it with no harm, guaranteed. One guy in Poland found that was the only way he could get his 2nd generation to run correctly. And the ECU he had, didn't care about the code (Poland doesn't have the same requirements as the US), so he is running that way to this day. I believe what the ECU does, is, knowing the TPS is disconneted, it is bypassed. If in, it will use the info.

MudHippy

No arguments, comedic over-tones, bordering on megalomaniacal tyranny, at times. These episodes, when merely periodic, can lead to "good" things. I'm out the door at this very moment, to start my truck. She'll need to warm, before I apply rdHarpers treatment. Thank you sir, by the way.

JEBSR5

Good to know, I go out and unplug it and drive to work in the morning. Hopefully this will tell me something. I suppose if it works, then I have been driving for 200K for nothing just to find out that I may have a faulty TPS or possibly out of tolerance piece of electronic.

JEBSR5

MudHippy, you're alright. Wish I had that kind of attitude.

JEBSR5

Disconnected TPS and other than high idle, really can't tell any difference. Not sure why it idles around 1200 RPM. I've adjusted it back to 800 RPM, but next trip its back to 1200.
Maybe if I could keep it at 800, I could tell a difference.

Any ideas on what is going on?

rdharper

Ok. Make sure your throttle is returning all the way against the stops. The dashpot could prevent that (probably not as you had the symptom from the begining). I think the ECU is seeing the open condition, rather than the short, when your throttle is physically in the idle condition.

Had the same symptoms with mine. I ended up adjusting the TPS with the engine running. The idle position is a knife edge. What I did, maybe not the recommended method, was to loosen the adjust screws just enough such that I could move the adjust. You should see the low rpm condion, and, then the high rpm condition. What you want (this is counterintuitive), is the point where the high rpm case just barely is caught at physical idle. Tighten it down, and then continue to bring the rpm down just the way you did when the TPS was disconnected, with the TB idle adjust.

After a few such adjusts of the rpm, the surging should be reduced to less than a hundred around 800 rpm. Which is what you wanted, if memory serves.

May take multiple adjusts down (maybe the ECU relearning, whatever) over some period of time. This is what mine did. Surging at idle should continue to go down at the same time. Mine now sits at 800, and stays within a 100rpm band now. Also, and this may be coincidental, as other minor changes I made in the same time period, (mostly fluids) my mpg went up one or two mpg over the same period.

LS1Steve

mine does the exact same thing, I haven't been able to figure it out either. at my last smog check the guy had to retard the hell out of my timing just to lower it for the test.

I can adjust the screw till it bottoms out and when driving around, rpm returns to about 1200. i'll be keeping an eye on this thread!

it is most likely the TPS, heres a link on how to check it, I haven't had time
http://www.4crawler.com/4x4/CheapTri...l#Introduction

MudHippy

Well, mine didn't need it. I was experiencing normal operation it seems, idle only varying 25 rpm +/- 800. I like to fiddle with things anyway. Previous owner had idle way misadjusted, looks like I got it without TPS trouble. Good to rule out.

JEBSR5

I'll have to try it the way you are describing as I have tried the adjustment LS1Steve suggests in next post and checked twice after tightening screws and after mounting back on plenum. It's adjusted right according to those spec's, but it may be worn and can't be adjusted the conventional way thus indicating a need to be replaced. If it weren't so high, I would be willing to buy a new one to get it right on the money, so to speak. Yes, you are correct on the dashpot as that was the first thing I checked and it's not causing any problem.

JEBSR5

Tried this approach today. What a difference. I will attest that I definately had it adjusted right. Checked before changing anything and all specs were right on. With that in mind, loosened screws and adjusted knife edge and bingo. Works much better now. I have no idea what this indicates as far as being correctly adjusted according to OHM's, but being much better with knife edge motor running adjustment, unless OHM meter is way off.

TNRabbit

I'm going to throw this out; two other situations can cause erratic idle:

1. Crud can build up where the throttle body plate seats against the wall and allow additional air thru at idle. It only shows up after hot becuase the ECU is throwing additional fuel (cold start injector) into the engine before then, which masks a lot of these type problems.

2. Vacuum leaks are VERY common with the fourteen thousand miles of vacuum hose on these things. Go all over the hoses with an UNLIT propane torch; if it idles up when you pass over a spot, you have a leak there.

Good luck.

JEBSR5

Wise words, but
1. Clean as a whistle.
2. All hoses checked and some where replaced, although not leaking they were replaced due to age and hard as a rock in danger of breaking. No leaks found.

I'm having no problems with idle after knife edge method.

rdharper

It would be of some interest to see what the measurements are set to now. I'm sure they are VERY close to the spec method of setting the adjustment.

Could have made that check myself, but frankly, once I'd done the adjustement this simple way, and it worked, I didn't care what the "spec" said. The idea came from buying a working inexpensive TPS and understanding how it works and what it does.

Mine continues to work just fine, after 8 months or so.

JEBSR5

Was going to check those settings this weekend, but ran into a snag today. Went to start the vehicle and wouldn't start, turned over OK and acted like it wanted to start, but wouldn't. Checked ignitor, coil connections by removing and plugging back in. That didn't work, removed top of air cleaner (AFM) reached in and moved vane, it was OK then tried to start and it did. Got home and pulled one code (51). Not sure, but I think I may still have a TPS problem. No AC was on.

It's run fine since adjustment and last post date above using RDHarpers method of adjustment on TPS. It's actually ran better than it ever has since I have owned it, til today. Still runs, just this incident and code.

Not sure where to proceed from here.

Oh yeah, the above connections were cleaned and lubed due to similar incident awhile back from a similar code about something didn't receive rpm trigger for a period of time. Don't remember code, but the symptoms above were the same each time.

Mr. Harper, thanks for the education on TPS. It's never ran better and I think it could be possibly bad TPS at this point, waiting to hear some input on this latest development.

As I said, it runs fine now, but this is the second time it has acted this way in maybe 2 months.

rdharper

51 could be the TPS although I never got that code. I think you have another unrelated problem. But while you are on it, don't forget you can simply disconnect the TPS. It will then throw a code, but if the TPS is the problem, the vehicle will start and run fine with the TPS connector disconnected.

I'm wondering about the AFM. I never had a problem with the one on my '94 3vze, but I did have problems with the one on my '85 22rec. They work identically, and they do "wear out", as their is a phenolic plate with a little arm on it that acts as the pickup to tell the ECM where the gate is. If that information is not right due to wear on the phenolic plate that is being "read", then you will get odd symptoms, sometimes making the vehicle undriveable until the AFM is replaced.

The AFM is an expensive part, so following the checks available in the FSM, probably in Chilton's and probably available somewhere in this forum, is worth doing. They are easy if you can use a DVM. Note that if it is starting to wear, the problem may not show up except in a slow sweep from closed to open. In that case you are looking for a "jump" in the reading indicating a discontinuity in the contact to phenolic plate.