Intake Manifold Snowball Effect? Help!

[siml8r5]

Here's my story...

 

I bought a 99 Silverado 1500 w/ 5.3L V8 in 2001. Last winter, my truck started surging really badly in the cold weather. When starting cold, it would surge to 2500-3000 rpm and back down and almost die until it was at operating temp. Then it would surge minimally at idle. When I took it in, they told me that it was most likely a bad intake manifold gasket. When they told me how much it would cost for labor, I decided to wait. They told me it wouldn't be a huge deal, but that it needed to be done in the next year or two. So, I drove it with no problems in the summer at all and kind of forgot about it until the SES light came on telling me that bank 1 and 2 were both lean. Also in the last 2 to 3 months, the transmission felt like it was slipping badly when accelerating from a dead stop and between 3rd and 4th gear up a hill. So, this weekend, I bought a new gasket, plugs, wires and a new blower motor resistor. When pulling the manifold, I noticed that the bolts were VERY loose, so it could not have been running well. Didn't seem that bad, but after changing the gasket, it was better than the day I bought it in 01. Idle is smooth as a baby's butt and acceleration is unreal...oh, and the transmission problem is gone for some reason! When I started it up the first time, the SES light was out from me disconnecting the battery during the procedure. Drove it, ran awesome and took it back home to do the plugs and wires. Did the plugs and wires and it started throwing a code for a bad evap vent solenoid...so I changed that (PAIN IN THE ARSE!) and cleared the code. Got gas yesterday morning to fill the tank and drove about 30 miles to make sure all was well. No codes.

 

Woke up this morning, left for work and was excited to see that the SES light was still not coming back, so I thought things were great. Drove about 30 min to work and the SES light came back on. At lunch I went to Autozone to check the code and it was throwing p0430 which leads to a bad catalytic converter. WTF? I swear this is a bad dream. When I got out of the truck this afternoon, I happened to look at the gas gauge before I got out of the truck and it was almost a 1/4 tank down!!! Could a bad CAT cause horrible gas mileage? I'm scared to change the CAT when it might not be the problem, but it ran lean so long, could the cat be screwed now from running rich suddenly? I really could use some advice. I'm lost and don't want to blow $600 on a new CAT and now fix the problem. Oh yeah, and my state emissions test is due in 3 weeks. if it fails, I get my license suspended...fun!!!

 

 

Thank you guys so much for the advice in advance...I'm really lost and could use some help.

 

Mike

[mattgob86]

Have you changed your o2 sensors lately, this could be the problem with the cat code. the sensor is reading wrong and thinking that the cat is jacked.

 

And man that does sound like a terrible dream.

[siml8r5]

Have you changed your o2 sensors lately, this could be the problem with the cat code. the sensor is reading wrong and thinking that the cat is jacked.

 

And man that does sound like a terrible dream.

 

I was thinking of that...any way to test them with a code scanner to see if one is bad? I just think it's really odd that all this happens right after I fix the gasket...

[jerseymike68]

interesting story!

[gmtech4]

code readers do just that ,it does not read data ,which you need ,take it to get diaged by a technician with a real scanner ,do not throw parts at it ,your only guessing ,I don't care what code it is ,one thing causes another ,a back pressure gauge will tell you in a split second if your cats are plugged but there are more things in play here ,good job on the intake ,it'll work out eventually!! good luck