[ryan_itt]

I have a 1990 GMC 1500 with a 350 TBI and I am having trouble with idling. when i first start it up its hard to start when cold then when the engine settles it starts to die then the computer (i guess) picks it back up and revs up and it does this for about 5 to ten min then settles down and just seems to idle pretty high. then yesterday i went out to start my truck and it would start then die right off then id start it back up and it run a lil bit then die then i give it some gas the next time i started it and when i give it any gas at all it will just die its like i hit a temporary kill switch then when i let off the gas it goes back to osocilating untill it just goes to idle real low and then dies. PLEASE HELP if you can. ANY and ALL help is appreciated.

i have a few mods to the engine like a new blueprinted and bored Throttle body unit, MSD 5 BOX, and others like exhaust and K&N filter, and roller tip rocker arms. the engine has about 154,000 miles on it and i know needs to be rebuilt due to the piston rings gettin burnt up.

 

[bigcheif90]

Ryan,
If your motor was completely stock I would tell you to check the coolant temp sensor to make sure it is installed/connected properly. A co-worker had a temp sensor fail in an 88 suburban (350 tbi) and the engine quit running, or would start but not continue running. I forgot to reconnect mine in my 88 (350 tbi) after I replaced the thermostat and the motor would not start easily, and if it would start it would not idle. Reconnected the sensor and it started right up and idled properly. I believe it is the connector slightly in front of the thermostat housing. I'm not saying this is your problem, just something I've experienced myself and very easy to check! Good Luck. Maybe someone might know how to check that sensor with a meter?

 

[edge]

IAC

Sounds like a bad Idle Air Control valve/motor. This topic has been covered a few times concerning TBI trucks. Greg Latvala and few other members are gurus at troubleshooting TBI problems.

A replacement IAC is not expensive. The coolant temp sensor is cheap too (less than $10) at Autozone, etc. I would replace these and see how it runs. Good luck, Ed.

 

[Restore60s]

Cold start

I think bigcheif is hitting it. Common failures with GM is coolant sensors. You need a scan tool to check the reading but when they go bad they are most of the time reading -52 degrees below zero. That puts the ecm in a full rich command because it thinks it's that cold. Timing gets changed real low to try and compensate. All that extra fuel would account for the stalling which with the stalling the Idle Air control is now in a hunt for a idle position. Seems like this problem always starts to happen when winter comes around but then again I've had Coolant Sensors show -22 degrees when it was 90+ outside.

 

[ryan_itt]

The coolant tem sensor is fine I got it all scanned and the MAP sensor kept coming up so i guess thats the problem