Need help sorting out no idle on new 5.7 TBI engine

[53charlie]

I have recently installed a new 5.7 long block in my '87 Chevy pickup. after i had the engine installed and connected i made a very stupid mistake (I was very tired!), first connected the positive cable to the negative battery terminal, and when i brought the negative cable close to the positive batt terminal, there was a big spark.
After i fixed this egregious mistake, connected the battery properly, turned ignition on, fuel pump relay kicked in for a few seconds and the engine started as long as i kept the foot on the accelerator. In fact i was able to do the recommended break in for the engine (2,000 - 2,500 rpm for 30 minutes), at that speed the engine runs smooth as silk. My problem is that if i let go of the accelerator the engine starts to miss, run rough and then stall. i have the timing somewhere close to where it needs to be, since i cannot set it at idle for now.
I have read the alternator diodes is the first thing to go when hooking battery backwards, but already checked those, they are fine.
I put in my spare ECM assuming something could have melted there, but no change.
Found IAC valve apparently stuck, replaced it, still no idle
This morning i verified the EGR valve moves in and out with vacuum, tried to start with EGR disconnected, nothing, disconnected and plugged the port in the back close to the distributor, still no start.
I have checked all four hoses that are connected to the base of the throttle body, all are solid with no breaks. If this is a vacuum leak, where else could it be?
The motor has a new Autozone distributor
I installed a new set of the larger 5.7 injectors, but I have tried to go back to the 5.0 injectors and made no difference.

I am running out of ideas on where to look, and i will greatly appreciate your recommendations.

Be well and stay safe,

Charlie

 

[Vbb199]

You must perform a IAC relearn after removing.

Go to ALDL plug close to hood release, jump ports A and B, turn key to "on" (not crank)

Wait maybe 10 seconds for IAC plunger to full extend.

UnPlug IAC,

Turn key to "off"
Wait a moment, turn truck back on.

If truck doesnt turn on, facing the firewall from the engine bay, on the far right of the physical TBi, you will see what looks like a mini freeze plug, dig it out.
Behind that reveals a torx screw.

That is what adjusts idle BEFORE the idle air control valve takes over

Screw it clockwise to open the butterflies for a higher rpm idle, keep adjusting and trying to crank until the truck will run.

If you have a tach, set between 6-700 rpms

Once thats done, turn truck off, plug IAC harness back in, disconnect battery, , remove the ALDL jumper, wait 10 min maybe, reconnect battery (correct terminals lol), fire the truck up.


Try that and see what your results are.

 

[Vbb199]

^ thats best done once engine is at operating Temp.

 

[53charlie]

Thanks so much Vince. I did as you recommended, i had to turn the idle screw to open the butterflies a tad, i this seems to have helped but the engine is still running very rough and had to keep it around 1,500 rpm or it died. all of this was done with the IAC disconnected, and while it was running the Check Engine light came on, codes 33 (MAP sensor signal voltage high) and 42 (bypass or electronic spark timing). would these be due to the IAC being disconnected? when i ran the engine to break it in for half hour above 2,000 rpm it did not produce any error codes. i have disassembled the throttle body a couple of times, i will go through it this weekend to make sure everything is right. the spray pattern of the injectors seems to be pretty clean and uniform but i will change the o-rings.

 

[Vbb199]

Thanks so much Vince. I did as you recommended, i had to turn the idle screw to open the butterflies a tad, i this seems to have helped but the engine is still running very rough and had to keep it around 1,500 rpm or it died. all of this was done with the IAC disconnected, and while it was running the Check Engine light came on, codes 33 (MAP sensor signal voltage high) and 42 (bypass or electronic spark timing). would these be due to the IAC being disconnected? when i ran the engine to break it in for half hour above 2,000 rpm it did not produce any error codes. i have disassembled the throttle body a couple of times, i will go through it this weekend to make sure everything is right. the spray pattern of the injectors seems to be pretty clean and uniform but i will change the o-rings.

Sounds like you left the IAC unplugged?


After you set the idle manually, you have to plug the IAC back in, disconnect battery, thus resetting ecm, connect battery again and start it up.
The IAC controls the idle. You just have to manually set it first with it disconnected.


did the truck run with the ALDL ports A and B jumped?

If youve done the above and still have issues, next id look into vaccuum leaks or CTS (cts voltage)
What does the exhaust smell like? Excess gas caused by a faulty CTS reading will choke it out.
Hook a vac gauge to one of ghe front port on the TBI and see what kinda vac it pulls (maybe while someone flutters the gas if it wont run) if its bouncing around, id start with the TBI base gasket.

Also, check your fuel pressure (its hard to do, i tap into the fuel filter with a spare piece of hose thats chopped off i have for checking tbi fuel psi)
You need 12 to operate.
Are both injectors spraying a fine mist? Or is it.... uh..... splashy? And uneven?

 

[Vbb199]

Code 42 is your ignition module possibly failing , its under the distributor cap.

 

[Vbb199]

Heres some good data i can share about diagnosing Code 42.

https://www.gmsquarebody.com/threads/87-91-chevy-tbi-issues-code-42.29926/

 

[53charlie]

Thank you again Vince. I thought that the "minimum idle" is set with the IAC disconnected, that is what i was trying to do, but the engine is running so rough that i am nowhere near setting a minimum idle nor able to set the timing.
One thing i try to avoid (apparently not very successful in this case) is to make several changes at the same time. I have a new long block, and i put a new distributor and new injectors, and on top of everything, I connected the battery backwards! if they engine does not run right, its hard to say what caused the problem. The old 305 was running fine (burning oil but fine) so i tend to think the fuel pressure is not the problem.
I had seen the code 42 one time before when i disconnected the little plug to set the timing, but as far as i know that is connected right now, i will verify that and will read the link you provided. over the weekend i will go through the throttle body one more time and i may even put the old distributor back just to take it off the suspects list.

 

[Vbb199]

Thank you again Vince. I thought that the "minimum idle" is set with the IAC disconnected, that is what i was trying to do, but the engine is running so rough that i am nowhere near setting a minimum idle nor able to set the timing.

Yessir, you are correct, but you want to aim for around 600-700rpms with no IAC.

One thing i try to avoid (apparently not very successful in this case) is to make several changes at the same time. I have a new long block, and i put a new distributor and new injectors, and on top of everything, I connected the battery backwards! if they engine does not run right, its hard to say what caused the problem.

Remember to handle 1 thing at a time and test your work!

The old 305 was running fine (burning oil but fine) so i tend to think the fuel pressure is not the problem.

That backwards battery mightve caused some damage to your fuel pump. Its definitely worth consideration friend!

At this pace, you have to forget everything you "thought" was good, and revisit it.

I know this is tuff to diagnose with a ****** running engine.

I had seen the code 42 one time before when i disconnected the little plug to set the timing, but as far as i know that is connected right now, i will verify that and will read the link you provided. over the weekend i will go through the throttle body one more time and i may even put the old distributor back just to take it off the suspects list.

Your timing bypass wire is a single plug over by the brake booster.

In my opinion , even with the electronic advance in bypass, and the IAC unplugged, it should still run.


Check your CTS voltage and check for vacuum leaks.

Hook a gauge to it and see whats up. If shes bouncy theres your issue.

 

[Vbb199]

@53charlie

Wonder if you fried the Ignition module under the cap, or damaged the coil when you hooked the battery backwards? Which by the way, thanks for being honest about that lol, nobody wants to admit when they made a mistake.


When the module dies, i dont believe itll run at all however.


I would investigate into vacuum leaks firstly since we've determined your IAC is "fairly" ok.
Make sure all the tbi vac ports are capped or used appropriately.

In regards to your EGR - even faulty the truck would fire up. (I would know)

Another thought to consider, while your 02 is rather dumb being a 1 wire, you dont have a chopped off exhaust or a leak at your newly installed primaries do you?

 

[Vbb199]

What does your exhaust smell like? Rich? Lean? This is important data on a tbi motor.

 

[53charlie]

Wonder if you fried the Ignition module under the cap, or damaged the coil when you hooked the battery backwards? Which by the way, thanks for being honest about that lol, nobody wants to admit when they made a mistake.

As I have gotten up in years (i am 67) i find it easier to accept my mistakes and even laugh at myself when i screw up. In fact ol' buddy, you seem to have some sway in this chat room, i propose the creation of a category up there with "Engine and Performance" and "Suspension" and we can call it "******* mistakes" for people like me to relate our screw-ups and how we fix them (hopefully!).
I think i am getting close to finding my solution. Yesterday i redid the IAC relearn procedure and now i can see the pintle has moved, allowing more air, so that is working. i can get the RPMs down to around 1,000 but at this point very uneven. injector spray looks very even (injectors are new) exhaust smells very rich, and the running is rough. although it does not sound like a uniform miss, i yanked a spark plug cable from the distributor and did not notice any difference. replaced that and pulled the next one, same thing, no difference. so the problem may be in the distributor.
on hooking up the battery backwards, i would think most circuits are protected by a switch (wipers have a switch, fuel pump has a relay, etc) so those should not be harmed if batt is hooked up backwards. But there obviously are some things that are "on" all the time. the fact that i got a major spark when i touched the terminal tells me current flowed (backwards) somewhere. So we will continue with the trial and error to find what got fried. I am ready to replace the module in the distributor with the old one, or maybe just replace the old distributor alltogether. But it has been raining all day here in Memphis and since i work in my driveway it will have to wait.
Y'all be well and happy Thanksgiving everyone

 

[Chevyguy]

As I have gotten up in years (i am 67) i find it easier to accept my mistakes and even laugh at myself when i screw up. In fact ol' buddy, you seem to have some sway in this chat room, i propose the creation of a category up there with "Engine and Performance" and "Suspension" and we can call it "******* mistakes" for people like me to relate our screw-ups and how we fix them (hopefully!).
I think i am getting close to finding my solution. Yesterday i redid the IAC relearn procedure and now i can see the pintle has moved, allowing more air, so that is working. i can get the RPMs down to around 1,000 but at this point very uneven. injector spray looks very even (injectors are new) exhaust smells very rich, and the running is rough. although it does not sound like a uniform miss, i yanked a spark plug cable from the distributor and did not notice any difference. replaced that and pulled the next one, same thing, no difference. so the problem may be in the distributor.
on hooking up the battery backwards, i would think most circuits are protected by a switch (wipers have a switch, fuel pump has a relay, etc) so those should not be harmed if batt is hooked up backwards. But there obviously are some things that are "on" all the time. the fact that i got a major spark when i touched the terminal tells me current flowed (backwards) somewhere. So we will continue with the trial and error to find what got fried. I am ready to replace the module in the distributor with the old one, or maybe just replace the old distributor alltogether. But it has been raining all day here in Memphis and since i work in my driveway it will have to wait.
Y'all be well and happy Thanksgiving everyone

Check your TPS. I did the same thing with the battery cables a month ago. I ended up replacing my IAC valve, TPS, and O2 Sensor. I will never let a neighbor touch my truck again. I thought my new alternator was fried, got lucky.

Sent from my SM-A705U using Tapatalk

 

[53charlie]

Hey Chevyguy, thank you. I have a spare TPS, i will just replace and see what happens. Are you saying the backward battery incident damaged the Oxygen sensor, or that was a separate issue? My O2 sensor is the single wire, which i assume works by varying resistance, and I don't think that there is any current to it when the ignition is off. i actually never did hook up the battery backwards, when i was about to hook up the second cable it gave me a major spark that is as far as that went. My alternator survived as well.

Vince, sorry for the excessive ignorance, i cannot figure out what you mean by checking CTS voltage

 

[Chevyguy]

Hey Chevyguy, thank you. I have a spare TPS, i will just replace and see what happens. Are you saying the backward battery incident damaged the Oxygen sensor, or that was a separate issue? My O2 sensor is the single wire, which i assume works by varying resistance, and I don't think that there is any current to it when the ignition is off. i actually never did hook up the battery backwards, when i was about to hook up the second cable it gave me a major spark that is as far as that went. My alternator survived as well.

Vince, sorry for the excessive ignorance, i cannot figure out what you mean by checking CTS voltage

No, my O2 sensor was just reading real slow on my scanner. It had been in the manifold since I rebuilt my motor 20 years and 40,000 miles ago.

Sent from my SM-A705U using Tapatalk