Problem with idle...jumps up and down, on its own.
 

I have a 99 Corvette with a 408ci. its has a ls2 ported 90mm TB. 6-speed. Car was running great. Made a 3 hour drive to FL last night mostly interstate. Once I got into town the car acted like it wanted to drive itself. with foot off the gas the car is revving between 1500-2500 rpms and as high as 3500 rpms. It threw a (reduced power )when it happened. But the only code i have is a P0507 & P0151. but im sure i remember a p1516 before i cleared the codes. the only work ive done to the car as of late was a Fast 102mm intake... Could it be a vacuum leak from the long drive? I would think if it was a vacuum leak the idle would be constant, not a up and down on its own.

Any help would be great, as im only here for 3 days for a wedding.

Eric

OK...So i pulled the Fast 102 intake off and cleaned the TB...took the whole intake apart and resealed the whole thing, new o-rings on the injectors. put the car back together, and i can hear the leak from the driverside very well....but its still there and there are no codes at all this time. what is going to be the best way to figure this out....im running out of time to play with this thing.

Thanks, Eric

U might need a retune .. My buddies ls1 cammed stalled needs a better tune.. It was running well then out of the sudden it started to do the needle jump at idle...it also started running a lil rich

Car has been tuned for the intake, sorry forgot to add that. Car was running great then bam started acting crazy.

My 98 Z28 did this and I had to replace the IAC. Not sure if this helps but it fixed my problem

well ive taken the intake back off...made room where the ARP head bolts were hitting. took the guide pins out (incase they where to long) and reflashed the tune. Its running better, but the car still wont idle steady (jumps around like i have a really big cam).

Sounds to me like ur iac ,and or clean ur maf. It might of gotten dirty for some reason on ur trip

I dont have an IAC on my car. Im running a 90mm tb on my corvette.

It might be a transformer.