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Discussion Starter #1
I have an intermittent problem with my 91 (3.9, TBI).... most of the time it drives fine, well, fine for a 91, but on occasion it won't accelerate from a stop. You hit the gas and the RPM drop off and if I don't baby the throttle it will stall, even babying it it will only accelerate extremely slowly and it will sputter and back fire.

It seems to happen more frequently when the truck is cold, the last couple days have been below zero in the morning and even tho I wait for the truck to heat up before I leave it still acts up for the first few lights I hit. After I get on the highway and the truck gets hot it's usually fine, but it does happen randomly on occasion.

Plugs/wires are new, oil is new, trans was checked out and fluid is new. I cleaned the TB as best I could without removing it.... I also put 1/2 a can of seafoam down the TB and the other 1/2 in about 1/8 of a tank of gas
 

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Turns out the TBI 3.9's use an IAC as the Magnum's. That's your problem, clogged or bad IAC.
 

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I have an intermittent problem with my 91 (3.9, TBI).... most of the time it drives fine, well, fine for a 91, but on occasion it won't accelerate from a stop. You hit the gas and the RPM drop off and if I don't baby the throttle it will stall, even babying it it will only accelerate extremely slowly and it will sputter and back fire.

It seems to happen more frequently when the truck is cold, the last couple days have been below zero in the morning and even tho I wait for the truck to heat up before I leave it still acts up for the first few lights I hit. After I get on the highway and the truck gets hot it's usually fine, but it does happen randomly on occasion.

Plugs/wires are new, oil is new, trans was checked out and fluid is new. I cleaned the TB as best I could without removing it.... I also put 1/2 a can of seafoam down the TB and the other 1/2 in about 1/8 of a tank of gas
Does it always happen after sitting for a period of time??
 
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Discussion Starter #7
doens't seem to matter how long it sits.... only really happens in the morning now on my way to work.... I have 4 or 5 lights before I hit the highway amd it happens almost every time i get caught at one... once I get on the highway tho I have no problems.

Doesn't seem to help if I let the truck warm up before I leave either....
 
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doens't seem to matter how long it sits.... only really happens in the morning now on my way to work.... I have 4 or 5 lights before I hit the highway amd it happens almost every time i get caught at one... once I get on the highway tho I have no problems.

Doesn't seem to help if I let the truck warm up before I leave either....
Been trying to get my head out of the MFI gear and get it in the TBI gear. Your TBI TB, IIRC, operates more off of vac than a MFI TB does. That being said, you may have have some vac galleys clogged up with carbon and just plain crud.

Remove the TB and check the bottom and ALL the vac ports for blockages. I may be all wrong in my thinking, but it may be worth a shot. :huh:
 

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Damn mines been doing this as well. My solution was let it idle for about 2 minutes before leaving :D

Guess its time to slip that V8 TB on :D
 
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Discussion Starter #10
I would take the TB off but there is A LOT of crap hooked up to it..... the problem is intermittent, if the vacuum was messed up wouldn't it act up more regularly?

It seems to come and go in patches, it drove like crap for the first couple weeks when I put in on the road.... then it was fine for almost a month, and now it's acting up a little again.
 
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I would take the TB off but there is A LOT of crap hooked up to it..... the problem is intermittent, if the vacuum was messed up wouldn't it act up more regularly?

It seems to come and go in patches, it drove like crap for the first couple weeks when I put in on the road.... then it was fine for almost a month, and now it's acting up a little again.
Could not be the problem, but you'll never know until you remove the TB to see. This was just a suggestion. :huh:
 

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I had a similar problem several years ago with a '77 Olds Cutlass. It would cough and sputter on acceleration. Anything more than light throttle and it would stall. Always restarted. It turned out to be the distributor pick-up had a broken wire. I put in a used distributor and it never acted up again. Didn't figure it out until it died and wouldn't restart.
 

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A cheap idea might want to run some Chevron fuel system cleaner through it for a couple tanks. TBI is one big fuel injector and if it's crudded up it won't get a proper spray pattern to atomize the fuel correctly. When you get on the gas it tries to dump more fuel in and ends up choking on big droplets of fuel instead of a fine mist. Plus it'll clean some of the crud off the valves.

And of course check all your ignition components... wires, cap/rotor, plugs, etc. Reminds me of when my wife borrowed her Dad's '91 Buick. It had a horrible idle and hesitation when accelerating cold. When I changed the plugs I asked him when he'd done the plugs last, and he said "change the spark plugs?"

A TBI or carb would be the only cars I'd ever put a TB spacer on, especially one of the "swirl" ones to help with fuel atomization...

MattB
 
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