i have a cam and it usually idles at 1500. got a 90 350 with tpi... hsr to be exact. i washed the motor the other day and it ran fine for a day so i don't think anything's wet. then i did an oil change and added seafoam to the gas tank and half the bottle to the brake booster vac line. i was going to work the other day and it ran terrible. it would try to die with any throttle and cut off on me for a millisecond every 1/4 mile like the cylinders all quit at once and came back alive. so i parked it immediately at a gas station, 10 minutes later started it and ran it in perfect condition home. i started it the next day and it idles up to 4000-4300. i tried to drive it like that about a mile hoping it would go down or at least throw me a code and no codes no fixes. i unplugged the ecm for 30 minutes while checking things out. all my vac lines are good, took the air filter off and throttle's working and closing. gasket's new on that. started, no codes/high idle. now i need help. all my connections are connected too.

 

IDK if an IAC will let it go all the way to 4k but you could check that.

 

any more ideas

 

Check for vacuum leaks under the plenum. Seafoam tends to eat gaskets.

 

ok solved. tested tps, and low voltage of 2.24 volts, high of 4.6

replaced it and idles great