LT1 acting weird

[FireChicken]

When Im driving around at say 40mph it tends to stay at higher rpms (3200 stall???) then when i let off it holds high rpms (like its engine breaking or something) for a second or two then suddenly and drastically drops below 900rpm or so only to shoot right back up to a normal above 1000rpm. At slow speeds such as coming to a stop or slowly reversing the car sometimes stalls. The idle can also get pretty bouncy from time to time at low speeds. The car has a pcmforless tune and the only code it throws is for the evap because they forgot to tune that out. Any ideas?

[Formula413]

My first guess would be the idle air control valve. You could try taking it out and cleaning it.

[ILuvPizzaTimes10]

TPS is fucking with the tranny shifting from the sounds of it. read the TPS reading on a scan tool.

seems like its holding in high gear thinking its at a higher pedal then it actually is. again scan all your sensors for normal range of operation.

[irockidz28]

not to hijack your thread or anything but my car does the opposite...if im driving at constant 40-ish the rpms will drop to like 800-900 and just chuggs like your driving a standard in too high of a gear...idk has done it since i bought it, pisses me off to no end, rpms come back up if i just barely press the brake. was told it was a stock converter, put a "lock-up delay" thing in it adn didnt help...end rant lol sorry good luck with yours!

[Suicidal racing]

Your rad low?..mine spit an piped an couldn't get out its own way one day..pulled over an motor was shaking an spitting..then she went back to norm drove around the block an all was fine..next thing i new she ran like a dog..parked her an she had a miss at 3500rpms..i figured it was my opti at first but more i read i could of been the rad senses..i never tucked around to check for sure though..said f it im going carb

[84ta406]

TPS is fucking with the tranny shifting from the sounds of it. read the TPS reading on a scan tool.

seems like its holding in high gear thinking its at a higher pedal then it actually is. again scan all your sensors for normal range of operation.

Agreed, that was my 1st thought..

It's pretty simple to test:
Take a paperclip and backprobe the connector going into the TPS, you're going to need to know which is the signal wire.. try the middle one 1st.

Use a Voltmeter and move the throttle with the car keyed on ONLY. It should be 0 at rest and 5v or just under(4.8/4.9) at WOT. You can test for deadspots or issues if you slowly move the throttle and notice a dip in voltage.

Repeat test with the car RUNNING and see if theres any spikes, or dips or anything. If the TPS is the problem you'll find it doing it this way.

Would be awesome if you had a scope or a graphing multimeter though lol

[FireChicken]

Thanks for all the quick replies guys. I will try all that and let you know how it turns out!

[DemonWithin99]

it's an LT1... could be the cold air... lol

[jayws6]

well if your close buy or willing to drive I have a GM tech 2 ,and a scanner tool that reads data of all sensors just get my number from the members page or pm me .

this way you see all data with out back probing the connector

[ILuvPizzaTimes10]

^^^^^ best possible way to see what's going on!

[84ta406]

Tech 2 is awesome!