This is not a third gen but is related since it's my tow vehicle. On my 95 Tahoe I have a rough idle and a code 35. The SES light is on only in Park at an idle. Code 35 is IAC valve but I have changed that out twice. When it is running there is a nasty smell coming from the exhaust like rotten eggs. I just did a tune up with all AC parts. Set timing and everything. Also, the gas mileage isn't too good either. About 12 mpg.


1. Will a bad catalytic converter cause a code 35 or do I have a vacuum leak?

2. Do I have 2 problems? Vacuum leak and a bad cat.

 

Rather than the Tech/General Engine forum, I'll move to TBI.

If the boys there let it live, it will live.

 

We will pretend that your TBI is in a 3rd gen since it is no different than the truck line-up. Rotten eggs are a sing of a bad cat. How does the vehicle run overall. Does the cat glow after you have been driving awhile. Dissconnect the cat and let the exhaust run open and see what that does. Did you play with the IAC at all when you intalled it? There is some good info on adjusting the IAC in the stickies above.

 

First of all thanks for not locking this because I really need help with this. It runs fine overall but just at idle it sets the SES light off and runs extremely rough. As soon as you put it in gear and take off it shuts off the SES light. I plan on getting the cat replaced or deleting it altogether since I have no inspection here. Also, why is there two air cleaner studs on this tbi instead of just one? Is it different? The cat doesn't really glow after driving it. I also did all of the adjustment and calibration like the instructions said to do. My original thoughts were that I have a leaky intake gasket.

 

The truck TBI's had two studs. I believe it was because the air cleaner housing was much larger and the intake tube went into the fender. It just makes it more stable that way. It still has the middle provision for a single stud if need be. Did you replace the 02 sensor during your tune-up? A bad 02 can cause a car to run really rich when warm and not throw a code.

 

The parts guy gave me a one wire O2 sensor instead of a 3 wire. He has ordered the correct part and that is next on my list.

 

TBI's use a single wire. I wouldn't worry about a 3 wire 02 just yet.

 

There is a 3 wire on there now and I just wanted to replace it with what it came with.

 

Yeah the newer vehicles came with the 3-wire sensor. Sounds like to me your cat is on its way out. I say your iac code is because your ecm is having to open your IAC all the way up to keep the motor idleing, hence tripping the light. Once moving the ecm won't really know why or care why the motor is running like crap. We had the cat go out on our 2000 blazer and it didn't trip a light till the cat blew into the muffler, even then it only came up with a smog error. The newer vehicles use a 3rd sensor to monitor smog.

 

The last of the TBI trucks did?

 

don't quote me on that, but my buddies 95 did, and all 96 and up did.

 

I know this thread is kind of old but still am battling this problem. I now have a new O2 sensor and a new cat that I just put on tonight. Runs much smoother and has a definite increase in power but still at idle the iac code turns on. It comes on at stop lights and go's off when you take off. It comes on in Park also.

 

I've got this figured out now. I pulled off the throttle body and found that the throttle body gasket was blown out. This was the problem all along.