Rough idle - Hard starts - Cold starts

[SoCalSlaughter]

Always something with this truck.. haha Well the truck is a 1990 Chevy V2500 4X4 Suburban, 350 tbi. The truck recently has been having a problem during cold starts. Go to crank and motor will turn and it will try to run, but stumble and die. It will only run if I hold the gas slightly. After holding the gas for awhile til it starts to warm up, I can then let off the gas and it will stay running on its own. Also, once it is warmed up, and I go to the store, or get gas, and go to restart the truck, it will turn over and run just fine, but starts up with a low idle, about 500 rpm. Once I throttle it the idle will come back up to around 700 rpm. Put the truck in park after its warmed up and the idle will be around 1100 rpm. I also noticed a drop in gas mileage. ALSO! lol I notice when the truck is started cold, it has a slight miss. I can hear a pop or puff from the exhaust every few seconds until it warms up then seems to run better. Ive already swapped out a IAC unit, reset computer, sprayed carb cleaner around tbi and intake. Thanks!!

[Lee H]

Is the check engine light on or been on recently? When was the last time it had a real tune up?
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[SoCalSlaughter]

No check engine light, last time it came on for for a code 42. That was about 3 months ago. Hasnt come on since. And the dizzy cap, plugs, wires, oil, pcv, and coolant was changed about.. 2 months ago? The truck had been running fine since all that was changed.

[Rollo McFlurry]

A 1990? I thought they all ran like that.
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[68gmsee]

Lot's of possibilities on these: fuel injector, TPS, fuel pump (check pressure), MAF sensor, ecm, on and on. Best thing is to take it in to have everything checked out so it won't cost you an arm and a leg replacing all the sensors.

[Special-Ed]

Iac valve. It's a stepper motor with pintle and seat. Take it off and clean the surface

Also with motor off make sure the trottlebody and butterfly are clean.
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[Marv D]

Originally Posted by Special-Ed

Iac valve. It's a stepper motor with pintle and seat. Take it off and clean the surface

Also with motor off make sure the trottlebody and butterfly are clean.
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DITTO, The IAC is a problem with the early TBI. Carbon builds up on it and it doesn't want to come to 'rest'. If you start having high idle issues, the IAC is always suspect.

Also my old tried and true standby. Change the fuel filter!! If ANYTHING even starts to be a hit of a problem on the TBI motors I change the fuel filter (even if it's only been a few months since changing)