Idles too rough for components selected
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Supreme Member
Joined: Sep 1999
Posts: 7,072
Likes: 13
From: Philly, PA
Idles too rough for components selected
Just finished my brother's Miniram-injected 409ci GTA motor swap. It runs good but even after an hour of driving around the ECM doesn't seem to have learned how to idle this thing smooth.
Its got a tiny cam in it. In my carbureted engines it idles dead-smooth, indistinguishable from stock.
Yes, I have a custom chip for it- TPIS burned it for us to match the larger cubes, cam and bigger 32# injectors.
The valves are adjusted correctly. I have checked for and not found any vacuum leaks. Anything over it's 700RPM idle speed it's smooth as gless and all the block learns are very close to 128. Just doesn't want to idle smooth. The idle speed seems to search up and down constantly.
Diacom says everything's clean and green- TPS voltage dead-on (.67V). Timing's right- 6* initial with timing wire disconnected, more with it connected. Knock sensor is not piking up any false knock. Nothing's leaking, squaking, smoking or scraping.
Ideas?
Its got a tiny cam in it. In my carbureted engines it idles dead-smooth, indistinguishable from stock.
Yes, I have a custom chip for it- TPIS burned it for us to match the larger cubes, cam and bigger 32# injectors.
The valves are adjusted correctly. I have checked for and not found any vacuum leaks. Anything over it's 700RPM idle speed it's smooth as gless and all the block learns are very close to 128. Just doesn't want to idle smooth. The idle speed seems to search up and down constantly.
Diacom says everything's clean and green- TPS voltage dead-on (.67V). Timing's right- 6* initial with timing wire disconnected, more with it connected. Knock sensor is not piking up any false knock. Nothing's leaking, squaking, smoking or scraping.
Ideas?
Member
Joined: Jan 2001
Posts: 165
Likes: 0
From: CT, USA
It sounds like the same problem I'm having with my 355 w/ cam. I have no idea whats wrong with mine either. Maybe your engine is just so nasty, that it doesn't wanna run smooth 
Another thing is maybe the IAC is toast.
------------------
1990 Pontiac Formula 350
Rebuilt 355
COMPCAMS 212/212 .440/.440 cam
Flowmasters 80 series.
Another thing is maybe the IAC is toast.------------------
1990 Pontiac Formula 350
Rebuilt 355
COMPCAMS 212/212 .440/.440 cam
Flowmasters 80 series.
Supreme Member
Joined: Nov 2000
Posts: 1,078
Likes: 0
From: San Antonio, TX
Car: Damn
Engine: This
Transmission: New Stuff
TPS voltage at .67? I don't know what year your car is or if the systems are the same, but mine is right at .54 at idle. I know that is what mine is supposed to be at stock.
But even though, a high tps setting would just raise idle speed, which would help your problem.
I too have idle problems with my 356. It idles up and down roughly between 500-700 rpms. Maybe your solution can help me.
good luck
------------------
'88 RS (originally 2.8)
-350, .040 over, vette alum. L98s, stock tpi.
-305 injectors & chip
-TES headers & edelbrock cat back
-3.73 gears, 700r4.
Best with 2.8-17.4@77mph
Best with 305-15.0@93mph
Best with 356-13.7@101mph
on a 2.050 60 ft.
(Damn the 2.8!)
But even though, a high tps setting would just raise idle speed, which would help your problem.
I too have idle problems with my 356. It idles up and down roughly between 500-700 rpms. Maybe your solution can help me.
good luck
------------------
'88 RS (originally 2.8)
-350, .040 over, vette alum. L98s, stock tpi.
-305 injectors & chip
-TES headers & edelbrock cat back
-3.73 gears, 700r4.
Best with 2.8-17.4@77mph
Best with 305-15.0@93mph
Best with 356-13.7@101mph
on a 2.050 60 ft.
(Damn the 2.8!)
Senior Member
Joined: Apr 2001
Posts: 725
Likes: 1
From: Norhtern NJ
I just fixed the exact same problem couple of days ago. As 90Form said my IAC was broken completely and as soon as I put a new one in everything started working just peachy (by my car's standards ) A nice smooth idle at 6-700Rpms.
) A nice smooth idle at 6-700Rpms. 
Banned
Joined: Jul 2000
Posts: 1,157
Likes: 0
From: Columbus,OH
My 355 just had the SLP TPI cam in it and it didnt idle smootly it bounced from 500-700 rpm when it was warm. I just learned to live with it, funny thing was when I put the 58mm TB on later if started to idle smoothly.
what is you IAC count maybe it just can't feed an engine thatenough at idle to do it smoothly? Thats what my problem was.
------------------
89 Trans Am Turbo 3.8L All stock 43,000 miles #1053 of 1555
Past Thirdgen:
86 Trans Am w/ built 355TPI with SLP goodies and too much other stuff to List. One sweet *** car, wish I would have had a good enough Job to pay insurance on three cars so I could keep it, but for a 89 Turbo Trans Am w/ Low miles, I think I made the right choice!
what is you IAC count maybe it just can't feed an engine thatenough at idle to do it smoothly? Thats what my problem was.
------------------
89 Trans Am Turbo 3.8L All stock 43,000 miles #1053 of 1555
Past Thirdgen:
86 Trans Am w/ built 355TPI with SLP goodies and too much other stuff to List. One sweet *** car, wish I would have had a good enough Job to pay insurance on three cars so I could keep it, but for a 89 Turbo Trans Am w/ Low miles, I think I made the right choice!
Moderator
Joined: Jan 2000
Posts: 19,655
Likes: 309
Damon,
I'm leaning toward the IAC as well. I'm assuming you set the throttle minimum air position, and the IAC passages were clean.
Your IAC may be sluggish due to dirt or a dry rack gear (the "screw-looking" portion of the pintle that engages the stepper motor racks). You might try removing, cleaning, and lightly lubricating the IAC gearing.
What TB are you using? It is possible that you are starving the larger engine for idle air, but a properly adjusted minimum throttle position should accomodate that.
And unless you have a 1990-later TB, the TPS should be a little lower.
------------------
Later,
Vader
------------------
"Let the bodies hit the floor!"
Adobe Acrobat Reader
I'm leaning toward the IAC as well. I'm assuming you set the throttle minimum air position, and the IAC passages were clean.
Your IAC may be sluggish due to dirt or a dry rack gear (the "screw-looking" portion of the pintle that engages the stepper motor racks). You might try removing, cleaning, and lightly lubricating the IAC gearing.
What TB are you using? It is possible that you are starving the larger engine for idle air, but a properly adjusted minimum throttle position should accomodate that.
And unless you have a 1990-later TB, the TPS should be a little lower.
------------------
Later,
Vader
------------------
"Let the bodies hit the floor!"
Adobe Acrobat Reader
TGO Supporter
Joined: Jul 1999
Posts: 10,907
Likes: 4
From: The Bone Yard
Car: Death Mobile
Engine: 666 c.i.
TPS voltage of .67 volts is well within tolerance. My car idles @ .65 volts and its been like that since the day I bought my car in 1991 (also it is SD so you cannot adjust it).
A few guys have found this problem, including myself. It's an eprom problem and the easy fix is to adjust the IAC Idle Step Counts vs Coolant Temperature Table in the eprom. What I noticed when my car was doing this is that the IAC Idle Step Counts defined in the table versus was quite a bit off from the IAC Step Counts I got when my car was idling.
Also, if you are running an T-stat of any temperature lower than 195*, the eprom needs to have the IAC Learn Minimum Coolant Tempereature adjusted in the eprom to ensure the "learning" of the IAC is working.
This for SD, but there are similar tables for MAF. I would capture the data and then fire it off to TPIS to re-burn you a new eprom as TPIS eproms are "customized" in such a nature that they are not readily changeable using standard BIN Editors.
A few guys have found this problem, including myself. It's an eprom problem and the easy fix is to adjust the IAC Idle Step Counts vs Coolant Temperature Table in the eprom. What I noticed when my car was doing this is that the IAC Idle Step Counts defined in the table versus was quite a bit off from the IAC Step Counts I got when my car was idling.
Also, if you are running an T-stat of any temperature lower than 195*, the eprom needs to have the IAC Learn Minimum Coolant Tempereature adjusted in the eprom to ensure the "learning" of the IAC is working.
This for SD, but there are similar tables for MAF. I would capture the data and then fire it off to TPIS to re-burn you a new eprom as TPIS eproms are "customized" in such a nature that they are not readily changeable using standard BIN Editors.
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