*Car details :91 Z28 that is bone dry stock (exhaust and all) with the automatic TPI 305 with 140k on the clock.

Recently I have been having an issue with bucking after roughly 10-15 minutes of driving. It has stalled when bucking when changing from "drive" to "reverse". Luckily it just barely started enough to back it in my spot. It runs great then starts bucking after a little bit of driving then gets progressively worse if I keep going, the idle in "park" is extremely rough. If I shut the car down after it starts bucking it won't start and sounds like the car has absolutely no life at all. If I let the car sit for atleast 2 hours or long enough to cool down completely it starts up and would run like nothing is wrong for the rest of the day.

*Note: this happens atleast 1 to 3 times a week. When a whole week without the problem last week until friday. I noticed that if I don't really get on it at all and drive 100% civilized it doesn't act up as often. It doesn't buck when not on the accelerator. It has been showing me that the engine has been getting hot but not 100% sure if the gauge is accurate because my cluster is off and on on the speed o meter and 1/4 off on my gas gauge.

** My buddy and I were thinking a clogged cat or muffler. I ordered the Borla cat system for now and thats on its way. Hoping that will help. It has had a metal on metal sound coming from the exhaust but I hadn't had the $ to take care of it untill recently.

Any idea what is going on? Thanks for any help guys!
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Any new word on this issue?

 

Do you have "Check Engine" light on? Might be A bad coolant temp sensor whacking out and telling the ECM the wrong proportion of Fuel.

 

could be a fuel pump on its way out. that's why it runs fine when it first starts. does it run better on a full tank of gas?