SURGE AT 35 MPH..IT HUMS AND STOPS ONCE I LET OFF GAS

[AZCertified]

Hi, I'm Brandon...If anyone could lend an opinion, i would greatly appreciate it...so..the car runs FINE..that is until i throttle up to about 30-35 mph to keep it at 35 mph...the car jumps down to 1500 rpms and a noticeable humming/slight grindin noise is heard..still will pick up speed, just slugishly and the noise intensifies while trying to throttle through it...when i release the gas pedal it stops immediately..then i can re-apply the gas and throttle normally...it also stops when i tap the brake pedal while throttling as well...in fear of wasting money...i haven't done anything yet besides cleaned the throttle body really well...and changed the TPS...which resulted in minimal difference...could it be the throttle body itself??...because when i open the butterfly plate...then let it go it kinda bounces back when i release it instead of a snap/pop lol...TCC solenoid or some sh*t..lol someone help me..

[Zeik75]

Try the catalytic converter first it sounds like that could be plugged. If you get under and tap it and hear rattling it is bad. I would start there first As it doesn't sound transmission related to me.

[AZCertified]

Ok...so before i just change it ill be sure to knock on it a little...is there anyway to clean/unclog/repair the converter or is changing it the only way..? See i work at Autozone so i know cat converters can get quite expensive...Thanks man...i kinda ruled the converter out because i thought the converter wouldnt show the symptoms im having...i appreciate it man

[Zeik75]

No problem.

As far as i know there is no fixing a bad cat, however you can get an aftermarket one for about 80 bucks. Don't go OEM it's a waste of money i know there is a magnaflow heavy metal cat that works for our cars and won't throw a code. Ill try to dig up the part number.

[Zeik75]

Here is a link for one CAT that will work without throwing codes.

http://www.amazon.com/gp/aw/d/B001HMJUD ... 25410_item

If you determine that the cat is fine let us know and we can probably figure it out.

[Zeik75]

Also i think the humming/grinding noise you mention is just a normal 3800 noise. Both of mine will make a low hum when under load at low rpm's but moderate speeds. Usually the torque converter kicks in and more of the engine vibrations will be transferred to the rest of the car. A slight incline where you would be going 45ish but in 4th gear for example.

[AZCertified]

Thank you guys so much...ill change the cat con with the one from amazon and ill post here and let you know how it goes...and people have been telling me it is normal...lol i wouldnt know exactly...because the three pontiacs i owned before this one were 4cyl...this is my first 3.8...anything else anyone suggests to do to it being new to a 3800..?

[Zeik75]

Lower intake manifold gaskets, get the new style aluminum ones and change the coolant elbows. Both are a plastic that doesn't get along with dexcool and the intake gaskets can hydraulic a cylinder.

Here is a general list.
http://www.pontiacbonnevilleclub.com/fo ... 40156.html

2000+ common problems:
http://www.pontiacbonnevilleclub.com/fo ... 25362.html

Torque specs: http://www.pontiacbonnevilleclub.com/fo ... ic215.html

[bfaye87]

Will that cat converter work for the 1999 SSE? I am looking for a new converter... just wondering, I am not a mechanic so just trying to find one that will fit right before I go spending over $100 on a part?

[Zeik75]

Start a new thread please!

But it would work as long as the pipe diameter is the same, idk if it is though.