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2000 chevy impala 3.8 . after the car sit’s and cool’s down the gas pedal or I should say the throttle plate sticks closed .bunch it once and it’s fine until it cool’s down again . I cleaned the throttle body twice but it still does it so I was thinking since I don’t have anything to loose maybe I would port and polish the throttle body . but my question is . is it worth doing that ? does it really give you more crisp throttle and a touch more hp. ? I most likely will put a new throttle body on it but I thought i would experiment for the fun of it .
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If you make the throttle opening larger without precisely fitting a larger throttle plate, the throttle will no longer seal when closed. This will cause a high idle which will also cause a check engine light when the computer determines it’s no longer possible for it to regulate idle speed to the specified range. Looking for a performance gain by upgrading the throttle (whether properly or improperly) on a otherwise stock engine is also not going to turn out to be a useful effort.
Just give it a polish , porting it will give the problems outlined above , and if can find find that has been ported to suit your car the PCM will play up , and you may find your transmission won’t shift quite as good .
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before you polish that throttle body consider this, if you have the N/A L-36 3800 series II engine, the Supercharged L-67 Series II has a larger throttle body that will bolt right on, get a new throttle body, or maybe one used or used and clean it up make sure it works correctly, bolt it on… this may…. give you a little more top end power, but also consider the fact the 3800 has long narrow intake runners going to each cylinder inside the upper intake plenum, so naturally its going to have a lot of low end pickup naturally, you trying to get more top end power with a throttle body will have little effect on performance, especially polishing.
in this process you can kill two birds with one stone, properly replace a sticking throttle body, free up any restriction that may be caused by the smaller N/A throttle body.
If you go the L67 TB route, remember that the L36 upper intake opening is oval shaped, while the L67 TB outlet is round. You’ll need to fill the openings on the back of the L67 TB with rtv, and use an L67 gasket to get it to seal. You’ll also need a tune for the additional airflow, your ltft’s will be positive for sure.
When porting/polishing the TB, you don’t touch the area around the blade for reasons mentioned above. Just the inlet and outlet, but that won’t solve your problem. Your EGR is what’s causing your TB to get gunked up, that’s one of the first things I remove on 3800 powered vehicles (makes plug changes easier, too). Can also use a tuner to set the egr disable air temp really low so it never activates, if you need it there for emission inspections.
If you haven’t done them already, your lower intake gaskets will need replaced at some point. They’re plastic, and the dexcool softens/weakens them, they switched to metal gaskets in the ’04+ 3800’s. Felpro makes a metal gasket set, that’s the one you want when you replace them. Attached a pic of a ’98 regal gs w/167k miles I did LIM gaskets on, completely shot. (Haven’t attached a picture on this forum before, so yeah)
Never knew the intake for the L-36 was oval ported, now i know…
Lower intake manifold gasket leaks on the 3800 are a very common known issue covered in my patter failures post, and its not just caused by the dexcool, i have seen cars converted to Glycol do it as well, including my old Regal. the simple issue is the gaskets are plastic as GrandPrix46 has stated, the engine gets hot and cold, hot and cold, the plastic gets brittle, and the little rubber parts that are designed to seal the coolant in crack and leak, it fails, coolant leaks out the sides of the engine from the intake manifold lower plenum or pool in the valleys through the bolts between the heads and the upper plenum, and worse case scenario the coolant leaks into the oil, and can ruin your rod and main bearings, shortening the life of your engine. The replacement gaskets have nice thick rubber seals much more adiquate for sealing than the thin rubber seals on the plastic gaskets, and the frames are made of metal, most mechanics i know recommend the Felpro brand, and that’s what they are commonly called “Metal Felpo intake gaskets.”
If you are going to replace the lower intake manifold gasket with the throttle body i would highly suggest also replacing the coolant elbows that link the lower intake manifold and front cover to the belt tensioner assembly that route coolant to the heater core, these are also made of plastic, and also get brittle and crack and leak, replace them with the newer aluminum replacement parts, for maybe a couple of bucks you will never have that issue again, VS having to frequently replace them, I have done this personally to my own Grand Prix.
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