Idles high after being in gear.

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BigRedOne

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So I am doing some more testing today and I think I'm narrowing down the problem just not sure what the issue is. I unhooked the O2 sensor to keep it in open loop to see if there was a difference. There was not. But I was still seeing O2 sensor voltage? WTF is that normal? Hooked it back up and did a base idle reset and just wanted to see what the computer thought when I played with the idle speed with the IAC unhooked. If I set it high it lowered the counts but never got below 13. If I set it low the counts would climb until I set it back under 750 and the counts would stop but not lower. This got me thinking. So I set the base idle to 700 with the IAC unhooked as per service manual. Left the IAC unhooked and put the truck in gear. Idle dropped to 500 and stayed there. it also stayed in open loop. Now I was watching the ecu trying to raise the IAC counts all the way up to 145. The O2 was reading 695. but BLM was still at 128 because it was in OPEN loop still. I reved the engine with the brake on up to 750rpm. It went into CLOSED loop and my BLM dropped to 115. This I believe means the engine is running RICH. Correct me if I'm wrong. And the IAC is trying to compensate for it. I also noticed that when I went back to park it idled at 700-750 no problem but it went back to OPEN loop.
So here is my thoughts on this. When I bought this truck it had been sitting for awhile only being moved around the lot it was at. It ran good but was sluggish. On my way home it ran out of gas. Gauge was froze at 1/4 from sitting unmoved for so long. When I filled it up I ran some fuel system cleaner thru it. It ran like **** after about 20 miles. I changed the fuel filter and it was full of crap. Figure the fuel system cleaner loosened up a bunch of stuff in tank and lines. so I ran that tank down and changed the filter again and It was better but it still ran kind of ruff. I figured it got into the injectors. Their spray pattern was a bit irregular. So I did a rebuild kit on the tbi with new injector screens and they indeed had garbage in them. cleaned them and when I put them back in they had a nice even cone of spray. and the truck ran smooth. Problem solved. RIGHT? Well what if they are dumping to much fuel? although it runs good and runs great at WOT. I may have the base Idle set way wrong because they are dumping fuel. This would explain why my IAC counts in gear at 750rpm are at full open 145 counts. I don't have anyone to help at the moment but I have never had someone sit in the truck with it in gear while I watched the injectors to see if they may be leaking or dripping or I don't know what. Could it be as simple as Needing New Injectors? Wouldn't that be something. Just hashing this out while I type. If you have an opinion on this please speak up.
Thanx
 

BigRedOne

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IDK, it's a possibility. If you do buy injectors, make sure you get flow matched ones.
How do ya do that? If I get them from Rockauto or Amazon? This old of tech kinda hard to find a matched set isn't it? I know I need to be patient. I just want this ordeal to be behind me. I just don't like mailing my injectors out and waiting both ways to get them back with no way of moving my truck in the meantime. Wouldn't the ACDelco or Bosch ones be pretty close to the same? Or am I just hoping? lol
 

PlayingWithTBI

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This old of tech kinda hard to find a matched set isn't it?
Here's another site. He will rebuild yours or sell a matched pair. The link above doesn't appear to be for your engine. I don't know what happened, I thought I was clicking on the correct ones, oh well. I'm gonna delete the previous link.

 

Sabinoerc

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It went into CLOSED loop and my BLM dropped to 115. This I believe means the engine is running RIC
as long as BLM is not pegged in closed loop, I think it means ECM is able to see O2 respond as expected to changes in commanded A/F ratio. there are a lot of reasons in an old engine BLM may not be perfectly centered. I don’t think you can conclude your rich just on that.
problem but it went back to OPEN loop.
this is what I’d investigate. I don’t think it should be normally going back into OL, at least it should not on a year/engine like mine (93). If on your year it should stay in CL on hot idle and it’s not, something is causing that and that’s the clue perhaps to chase?
Could it be as simple as Needing New Injectors?
anything’s possible but it wouldn’t be my first guess. Your injectors aren’t changing between good case and bad. It could be fuel/injector related but it’s hard to hunt and peck these sorts of things without the data. Eg. I had a problem once where idle was surging and smelled rich. Problem was low fuel pressure. ECM was enabling some save mode at idle called something like “idle enrichment” or the like and dumping fuel to compensate for inability to stay in closed loop at idle
 

BigRedOne

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as long as BLM is not pegged in closed loop, I think it means ECM is able to see O2 respond as expected to changes in commanded A/F ratio. there are a lot of reasons in an old engine BLM may not be perfectly centered. I don’t think you can conclude your rich just on that.

this is what I’d investigate. I don’t think it should be normally going back into OL, at least it should not on a year/engine like mine (93). If on your year it should stay in CL on hot idle and it’s not, something is causing that and that’s the clue perhaps to chase?
Hey thanx for responding. My year (89) is supposed to idle in open loop according to the service manual. Also I read that anything over 600 on the O2 is pretty rich(mine is 695) as well as anytime BLM goes 115 or lower means it is trying to correct a pretty rich condition.

"anything’s possible but it wouldn’t be my first guess. Your injectors aren’t changing between good case and bad"

I don't think they are changing between good and bad. I think they are just running rich all the time. I think that when I'm setting the base idle that I am setting it with a real rich injector. So when I put in good injectors my base idle should drop to maybe 450-500rpm's. If I'm right my problem is that setting base idle with a rich running injector I am setting the butterfly's to closed. And with that same injector running rich the butterfly's never open enough therefore the IAC is working over time to correct and unable to do it. If the new injectors aren't dumping fuel I should have to open the butterfly's more to idle correctly and when in gear the IAC will only have to open a bit to maintain idle instead of going full open without result. I noticed while testing that every time I revved the motor the IAC count went up not down. This is what caught my eye as to a RICH condition. It's not overly rich enough to set a code but enough to cause the base idle set up to be off trickling over to overall drivability. It doesn't have black smoke. Just enough to mess the idle up.
Fingers crossed This is the answer. Ordered 2 remaned injectors for WED. thru amazon. At least with Amazon Prime if it doesn't fix the problem I can return them.
 

BigRedOne

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Edit to above rant. Actually the butterfly's may be open to far at Idle allowing to compensate for the rich injectors. The new injectors should be shooting less fuel therefor the Idle will rise when I swap them because the butterfly's are to far open. which will allow me to turn the base idle down closing the butterfly's more. Also if the injectors are rich the ecu isn't able to turn down the fuel delivery that it commands so the IAC is turned up to try and compensate? Just thinking out loud here. Realized I was thinking backwards about the butterfly's in above statement. I hope I'm right on this. My brain hurts as well as my pocketbook. lol
Just need this old girl to be right so I can start using it for what she was bought for.
Thanx for listening (reading) to me rant.
 

BigRedOne

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well that didn't work(new injectors). It definitely was running rich. It is now just barely running lean 131 BLM and 129 Integrator. Nothing to worry about. But it is still doing the same BS. it is still lugging way down when put into gear making the IAC open all the way to 145 to bring the idle to 750 in gear. But the IAC will not lower when you put it to park. And there is no reason for the IAC to be wide open in gear. I actually set the base idle in gear to 700 and tried this again to see what would happen. In gear, 750rpm, 22 counts on the IAC. That is what the manual says to do. Put it back in park 1550rpm and the IAC counts drop to 13 and the rpms settle at around 1450. So that's no good. Set the base idle back with it in park. 750rpm, 18 IAC counts. Good right? Put it into gear and drops to 500rpm the IAC raises its counts to 145 and achieve 750rpm. Back to park IAC stays at 145 and RPM shoot to 1750ish and stay there. What is telling this IAC to stay put? I put the old IAC back in with the same results. And why no codes to help trouble shoot this. You would think if the engine is reving high and the tps says the throttle is closed that it would tell the IAC to close or set a code. I don't know why the Idle drops so far when put in gear. Is that normal? from 750 to 450-500? I mean my other vehicles only drop maybe 50-100rpms before the ecu raises it back up to normal. Is something overloading the engine? if so what does that have to do with when its put back to park that it doesn't control the rpm anymore? Leaving the IAC open till you cycle the key. I now have more questions than before. I guess I need more detailed info. I'm going to have to buy a regular cable so my laptop can connect. I need to see live data of what the ecu is actually commanding. ALDLdroid is good but I have yet to find if and how I can see commanding info. Only what is actually happening not what its commanding. My brain and my patience hurt.
 

Sabinoerc

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I bought a cable from Moates and it worked for me. Probably can find it cheaper but they did have some “how to” stuff on site at the time which I found helpful
 
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