Idles high after being in gear.

[BigRedOne]

So I put a GM Reman ecu in. Seemed to be what a few people on other resources had issue with when nothing else worked. Well we can put that down as another thing that is new but didn't resolve the issue. I'm at my wits end here. The new ecu seemed to run smoother in the beginning as it learned its idle. Once warmed up I shifted to reverse and let it settle on idle there. Put back in park and Idles to 1000-1050rpm. Not as bad as before but still not right. Took it for a ride and let it learn cruising and excelleration all seemed good as usual drivablilty is good. Stopped and back to park and 1000-1100rpm. Turn key of and start back up 750rpm perfect. Back in gear and to park. 1000-1100rpm. WTF? Had a friend of mine who is a tech drive it. Did some slow and faster start stops and restarts. Same thing. But then we get back to my shop and he's playing back and forth to gear and p/n and it starts missing ever so slightly in gear put it in park and it revs to 15-1600rpms then settles around 12-1300rpms. and is running a bit rough. SHut it of and restart. 750rpm and purrs like a kitten. Any idea what could cause this? Is there a intermittent fueling problem that is making the IAC stay open cause its rich?
I rebuilt the tbi and put new screens on the injectors. At idle the cone of fuel looks good no drips no weird pattern. rev it up all looks good. Maybe different under a load?
Sorry for the long rant. Just throwing it all out there and hope someone has an ah ha moment that i'm not considering.

 

[Schurkey]

Had a friend of mine who is a tech drive it.

Did he drive it WITH a scan tool connected?

What is your fuel pressure? How old are the usual "tune-up" parts--cap, rotor, plug wires, spark plugs? EGR work right? PCV, air filter and fuel filter OK? Charcoal canister verified?

 

[PlayingWithTBI]

One thing, when you turn the engine off, the IAC goes to its park position, ~140 counts. Then when you restart, it goes to its commanded position which, gives you your 750 RPM. This is a long shot but, maybe your IAC is getting stuck until you turn off the engine? I don't think a scanner will tell you this since it's reading commanded steps for the IAC, there's no feedback for actual position.

 

[BigRedOne]

One thing, when you turn the engine off, the IAC goes to its park position, ~140 counts. Then when you restart, it goes to its commanded position which, gives you your 750 RPM. This is a long shot but, maybe your IAC is getting stuck until you turn off the engine? I don't think a scanner will tell you this since it's reading commanded steps for the IAC, there's no feedback for actual position.

It's a brand new AC Delco IAC. But I know they can be bad out of the box. The problem I have is this one acts just like the original I took out. And if it were getting "stuck" going back to its park position why does it do it without a problem when you cycle the key? Its as if something is tricking it into thinking it needs to be open. I need to set up a way to check fuel pressure. I rebuilt the TBI and the old Pressure diaphragm was corroded and stretched out looking. But there is no way to know if the new one is working properly with out a pressure tester. I need to make or locate an adapter that screws in between the fuel filter and feed line. I have braided line at the TB so I can't just spice a tee in up there.

 

[BigRedOne]

Did he drive it WITH a scan tool connected?

What is your fuel pressure? How old are the usual "tune-up" parts--cap, rotor, plug wires, spark plugs? EGR work right? PCV, air filter and fuel filter OK? Charcoal canister verified?

Everything is New. How do you "verify" a charcoal canister? I unhooked and plugged all vacuum to it. It made no difference. So I hooked it all back up again. Not actually sure what that does. There is no other lines that run back to the tbi or EGR from it. So what is it filtering? and does it return something to the engine? It seems only to filter air going to the vac port on TBI.

 

[PlayingWithTBI]

I need to make or locate an adapter that screws in between the fuel filter and feed line. I have braided line at the TB so I can't just spice a tee in up there.

This fitting goes between the TB and your braided hose. Then you need an 1/8" elbow and a gauge.

Our fuel psi guage to fuel line adapter mounts inline directly to your GM tbi throttle body!!!

Our fuel psi guage to fuel line adapter mounts inline directly to your GM tbi throttle body!!!

marine-performance-parts.com

It'll look something like this, along with an AFPR.

You must be registered for see images attach

You must be registered for see images attach

 

[Schurkey]

I need to set up a way to check fuel pressure. I rebuilt the TBI and the old Pressure diaphragm was corroded and stretched out looking. But there is no way to know if the new one is working properly with out a pressure tester. I need to make or locate an adapter that screws in between the fuel filter and feed line. I have braided line at the TB so I can't just spice a tee in up there.

Two common kinds of TBI fuel pressure testing adapters, and AT LEAST three kinds of Schrader valves--you need a Schrader valve fitting on the adapter that matches the threaded connector on the pressure gauge. There's two kinds of threaded Schrader valves, using different thread sizes. OTC and some others use a quick-connect style that doesn't thread onto the gauge.

One kind of adapter goes in place of the fuel filter. Remove fuel filter, install adapter. When done testing, put a fuel filter back in. I had to use one of these on a van, because the van had no clearance behind the throttle body for the other kind of adapter.
Example:

xc_hide_links_from_guests_guests_error_hide_media

The other common kind screws in-line behind the throttle body. Again, make sure the Schrader valve fitting is the same as what's on your pressure gauge. I bought the wrong kind, then had to buy a ten-pack of the other kind of Schrader valves to get it to thread onto my gauge.

GM TBI Adapter 7/16 | Actron

GM TBI Adapter for Professional Fuel Pressure Tester Kit CP7838.

actron.com

If you need the gauge, too, you can buy the second adapter with a gauge and some other adapters like this. This way you're sure the Schrader valves are compatible. The downside with this product is that the gauge goes to 100 psi, while the TBI works on 9--13 psi in most cases. The gauge has poor resolution when used at the bottom of the scale.

xc_hide_links_from_guests_guests_error_hide_media

Everything is New. How do you "verify" a charcoal canister? I unhooked and plugged all vacuum to it. It made no difference. So I hooked it all back up again. Not actually sure what that does. There is no other lines that run back to the tbi or EGR from it. So what is it filtering? and does it return something to the engine? It seems only to filter air going to the vac port on TBI.

The fuel tank vapors vent through the charcoal canister. The fuel fumes get trapped in the charcoal, then get purged by filtered fresh air drawn through the canister via the vacuum from the throttle body.

If the canister doesn't purge properly, it fills up with liquid fuel. The charcoal dissolves and becomes a gritty disaster in the throttle body--or worse yet if it's carbureted.

 

[BigRedOne]

Sorry its been a bit. Had to walk away from all the $$ I was hemorrhaging with no results. So I went and bought the proper fuel pressure gauge that Schurkey suggested and my fuel pressure is at 10.5psi in park and in gear and back to park. Unhooked the charcoal canister and no difference to idle at low or high idle. Down to the prom (chip)being bad. Again I don't want to waste money on one more thing that isn't the problem. Just not sure what else could be. I thank you all for your input and ideas. Where do I go from here? Thought about taking it a Chevy dealer and see what happens but I'm sure it will be $1k for diagnosis and still won't figure it out. The guys that ACTUALLY worked on these back in the day are few and far between or retired. New guys haven't ever seen a TBI like this. lol

Thanx again everyone for trying to help.

 

[Schurkey]

What results are you seeing on the scan tool?

 

[BigRedOne]

What results are you seeing on the scan tool?

Well I haven't been able to find a different scan tool that allows you to disable the 10k resister. The one I was borrowing tends to make the Idle better. But everything I did see while using it seems to be working. CTS is reading 189 in the scanner and my dash. IAC seems to be working just doesn't settle back to where it needs to when put into park from gear. Cycle the key and iac goes right to park position and idles no problem. P/N is shown on scanner and shows in gear and back to P/N as it should. Closed loop and Open loop shows to be working. TPS is showing .55 when idling in park or gear. Plug IAC hole and idles at base idle no problem(no vacuum leaks) . Lean /rich on scanner cycles back and forth as it should. Doesn't stay still. something is telling or not telling the IAC to return to idle table setting once in gear. If I warm it up idling in place. The rpms once I go into gear and back tend to be around 1050-1200. If I drive it somewhere when I stop and idle then go to park it tends to be higher like 1500-1900. I'm at a lose here. I'm going to recheck and reclean all the grounds at the tstat housing and I think Im going to replace the egr valve(even thou it passes testing) just in case there's a obstruction of some sort. Not sure why it Idles perfect in park when you cycle the key(all day if you let it) then when you go to gear and back it idles so damn high. Oh and if I hadn't mentioned it before. It idles about 700-800 in gear. But it is trying to idle higher which is what the real issue is. Fighting it in traffic with brakes it starts to get hot. If you let your foot of the brake it idles up to speeds of 20 or so mph. No codes for the chip(prom) but It seems to me that is the only thing left that would mis inform the IAC.