1987 suburban 454

[eat1sleep8blink2]

hi im new to this part of the forum i have a 68 burb and just got a 87 burb with factory rear air and a 454 tbi in it. but it has a really high idle like 3000 and i was thinking its the tps. but then i noticed it sprays alot of fuel constantly out of the injectors at idle an ideas.

[tvblazer78]

I would try replacing the idle switch on the side on the TPI. Some times they go bad.

[JEM]

Originally Posted by eat1sleep8blink2

hi im new to this part of the forum i have a 68 burb and just got a 87 burb with factory rear air and a 454 tbi in it. but it has a really high idle like 3000 and i was thinking its the tps. but then i noticed it sprays alot of fuel constantly out of the injectors at idle an ideas.

It helps to be able to do some datalogging out the ALDL port to see what voltages are coming back from the TPS, what the ECM sees as engine RPM vs what it's trying to command, and whether the IAC is where it should be.

I think you can check TPS voltages, etc. with a multimeter but it's so much easier to plug in a laptop if you're set up to do it...

Fast-idle after startup should be ~1200RPM or so, 750RPM in gear as it warms up (those numbers from my '91, expect all the TBI L19s are the same.)

Do you actually have a tach on it? The big fan on the things sound like they're spinning 3000RPM at fast-idle.

I assume you've checked the mechanical stuff like the throttle cable for binding and verified that the plates are closing. There's also a procedure for setting the base idle (shorting two pins on the ALDL to force the IAC closed, unplug the IAC to keep it there, then set the throttle stop for ~625RPM.)

Yeah, the injectors do look like they're spraying a lot of fuel at idle, but all the fuel in the world can't make it idle at 3000RPM unless it's getting air somewhere - throttle plates, IAC, or a big-ass vacuum leak - it'd just bog and run super-rich.

The 8600GVW 454s stay open-loop at idle and up to about 1500RPM IIRC though I've got mine going into closed-loop at ~900RPM right now, may play with closed-loop idle, it seems to work just fine that way with a heated O2 sensor.

[eat1sleep8blink2]

no it doesnt have a tach but ive been around bb before it might not be 3000 but its higher then 2000. i also think its the tps and i would hook it up to a computer if i had one but i dont got a scan tool.