For just over the past month my car has developed an issue where it will hesitate when giving it gas after a cold start. One the rpms settle after startup, when giving it light throttle, the engine will hesitate and sputter for a few seconds around 1200 rmp. If giving it heavier throttle, the engine will rev fine, but gives a nasty backfire when releasing the gas. What's driving me crazy is it will only do it once. After that initial hesitation/backfire the car will run fine, even if restarted. It idles fine and has to cool off for a few hours in order to replicate the issue. So far the plugs have been replaced and the maf and throttle body cleaned with no results. The only mods are a JLT CAI and tune (both of which I've had for years with no issue.) Any advice is appreciated. Thanks.

 

When was the last time you ran a tank or 2 of fuel system cleaner? How many miles on the car?

 

It's been about 1.5 years since I ran fuel system cleaner. 145k miles.

 

I'd try that before you begin replacing things. I run Techron every 10k miles or oil change, whichever comes first. And when i DO suspect an issue, I'll run SeaFoam thru.

I'd also replace the fuel filter if that hasn't been done in the last 30k-40k miles.

 

I'll try running some cleaner through the next two tanks once I run the current one down. Other than what I can check by opening the hood I am really hoping to avoid any exploratory surgery. Any recommended cleaner? I was leaning towards Gumout again.

 

A lot of people like Techron. I'm not a fan of Gumout. In your case, since you're not performing preventive maintenance, I'd use the SeaFoam.

 

Also clean the throttle body ...

 

The OP says he did that. But I'd probably do it again just to be sure.

 

Well, ran cleaner and even checked the throttle body (was still clean) and the issue persists.

 

Fuel Filter and Fuel Pump would be next on my list.