454 tbi won't idle when warmed up...

[Nodnarb76]

So I have been working at this for a while.
Problem is when truck is first started (cold) it runs fine, then when warmed up, and I let my foot off the gas pedal it dies. It will restart if I give it some gas ( press gas pedal just to be clear) while starting but then dies when I let off the pedal.

When this started I was getting a code 44 lean exhaust so I replaced o2 sensor, fuel pressure regulator, fuel pump, and fuel filter, even a new gas tank and cap.
And the problem remains.

Prior to this I have replaced: erg valve, map sensor, coolant temp sensor, and cap,rotor,wires,plugs.

Any ideas/suggestions?

[Wellgeo03]

Have you checked / tested the air idle control? Could also possibly be a dead spot in the TPS? Just throwing out ideas, but from your post these might be all you have left to check.

[Nodnarb76]

I've been reading about checking the IAC and I don't have a tach to adjust the idle using the screw on the front of the tbi unit. Any other way to check it?
Thanks for the reply.

[Nodnarb76]

Update, when the engine was cold it was running fine. I disconnected the IAC valve, and it has run fine ever since.
My guess is in the past I squirted some brake cleaner down into the IAC passage, and I may have ruined it. My thinking is when the motor is cold the pintle is retracted all the way. When it was supposed to extend, it went past where it was supposed to and was killing the motor.

[rfmaster]

Originally Posted by Nodnarb76

Update, when the engine was cold it was running fine. I disconnected the IAC valve, and it has run fine ever since.
My guess is in the past I squirted some brake cleaner down into the IAC passage, and I may have ruined it. My thinking is when the motor is cold the pintle is retracted all the way. When it was supposed to extend, it went past where it was supposed to and was killing the motor.

You can not ruin IAC with a typical carb cleaner. The stepper motor is a sealed unit. However, bypass air passage is a common area for carbon buildup which will effect idle stability. BBC TB tend to develop a vacuum leak between TB flange and intake right around the front area of the TB.

//RF

[Wellgeo03]

This is good to know. I am also having trouble with my TBI 454, but when cold. It acts like a poorly adjusted carb engine when cold.

I will be checking the same things out. Sensors, vac. leaks, and so on. I do have a minor coolant leak at the front of then intake against the drivers side head and wonder if that can cause my cold stumble issues.

[Desert1957]

Small Block Chevy / Almost the same as a 454


ALDL connector under dash



How to calibrate the TBI IAC Motor

1-Engine warmed up, key OFF, tranny in PARK

2-Put a jumper wire from pin “A ” to pin “B” on the ALDL connector (should be the black wire & white wire) A metal paper clip works good for this.

3-Turn key to ON, do not start engine , wait 10 seconds. This
will extend the IAC pintle and close off the air passage in the
body of the TBI. Remove the electrical connection to the IAC
by pulling it straight out. Turn the key to OFF and remove the
jumper from the ALDL connector.

4-Start engine, and let it settle into idle speed. You may need to give it a little throttle to get it running. Connect the scanner to the ALDL and check the engine RPM. You want the engine RPM to be at least 125 rpm less
than what the “target idle speed” is set for in the chip. Use the throttle
screw to obtain the “125 rpm less” idle speed.

Example:Target idle speed in the chip is 700 RPM less -125 minimum idle speed = 575 RPM

5-Turn engine OFF. Connect the IAC connector.

6-Start engine and run for seconds, turn engine OFF and wait at least 30 seconds. This will reset the IAC control.

7-Start engine, in PARK, let it idle. Idle speed should be close to the “target idle” set in the chip, if the IAC is being controlled by the ECM.


Desert

[Nodnarb76]

Originally Posted by Desert1957

Small Block Chevy / Almost the same as a 454
Attachment 1216503

ALDL connector under dash

Attachment 1216504

How to calibrate the TBI IAC Motor

1-Engine warmed up, key OFF, tranny in PARK

2-Put a jumper wire from pin “A ” to pin “B” on the ALDL connector (should be the black wire & white wire) A metal paper clip works good for this.

3-Turn key to ON, do not start engine , wait 10 seconds. This
will extend the IAC pintle and close off the air passage in the
body of the TBI. Remove the electrical connection to the IAC
by pulling it straight out. Turn the key to OFF and remove the
jumper from the ALDL connector.

4-Start engine, and let it settle into idle speed. You may need to give it a little throttle to get it running. Connect the scanner to the ALDL and check the engine RPM. You want the engine RPM to be at least 125 rpm less
than what the “target idle speed” is set for in the chip. Use the throttle
screw to obtain the “125 rpm less” idle speed.

Example:Target idle speed in the chip is 700 RPM less -125 minimum idle speed = 575 RPM

5-Turn engine OFF. Connect the IAC connector.

6-Start engine and run for seconds, turn engine OFF and wait at least 30 seconds. This will reset the IAC control.

7-Start engine, in PARK, let it idle. Idle speed should be close to the “target idle” set in the chip, if the IAC is being controlled by the ECM.


Desert

Thanks, I will need to do this once the new IAC arrives.
I have a friend with a code reader who will let me borrow it.

[kalbert]

Have you done the easy stuff like check for vacuum leaks? 8 out of 9 TBI idle and driveability complaints can be traced back to a vacuum leak. Stuck EGR, baked EGR base or intake gaskets, rotten hoses, worn throttle shaft bores. Don't relearn the IAC until you do or it will learn wrong and you'll really have trouble finding the problem.

[Nodnarb76]

Already replaced the tbi and adapter gaskets. Have replaced a few vacuum hoses. Where can I get the small hard vacuum lines that go from the tbi unit to the egr solonoid and from the solonoid to the valve.
They are really small and look like the are going to be hard to find.

[kalbert]

The hard plastic lines can be replaced with regular hose, so long as its not kinked and fits snug on the barbs.