High idle/sputter after warm start


New Member
Aug 23, 2015
Looking for some suggestions to help diagnose what's going on with my car.

I recently changed to 60# injectors, added a RJC Powerplate, and had my stock throttle body cleaned and ported to 62mm. I also had my chip updated to reflect those changes.

The car starts right up after sitting for several hours, overnight, or for several days. It idles where it should, and seems to run fine. However, when I try to start it after I drive it for a few miles and it gets warmed up and I shut it off and let it sit for a little bit, it doesn't immediately turn over. I have to crank it two or three times, and when it turns over, it sputters a little and then the idle shoots up to 1800-2000 rpm and doesn't settle back down.

I've read/heard to look for a vacuum leak, but wouldn't that affect it starting all the time and not just after it has warmed up?

Any help or suggestions are appreciated!
Yes and no. A vacuum leak will cause problems both hot and cold, BUT hot and cold have two different sets of operating parameters for fueling/spark/etc

There's a chance that you just get away with a leak better when cold than when hot.

I know that really doesn't answer your question, but vacumm leaks are VERY important to police on these cars. They can literally mean the difference between hauling ass or owning a POS.

There are many of these cars that still have the original lines on them and they honestly should ahve been replaced over a decade ago. Here's a quick test you can do...

Pop the hood and touch the ilnes running inside the drivers fender to the vac can, CC can, etc... If your fingertip turns black, replace the lines yesterday. Also blow through the check valves, if they won't stop air from flowing out, they're bad and allowing boost to reach areas that should never see pressure (like CC, charcoal can, HVAC, etc...)