So I just bought this 01 monte carlo ss and after bringing it home I discoverd a shake or shudder at around 35mph. At first it only did it when it was warmed up, but then it took a week off, and then it came back to where it will start acting up after driving for a min. then stop once it's warmed up. I read a service bulletin the other day on alldata saying the tps will cause shudders or "fishbites" at highway speeds so i took a chance and threw one on this weekend. Went all weekend with no problems, ran like a champ, but then it came back today. Only does it when driving slow doing around 35, and when you put a load on the car going up hills. Goes away once i'm on the open road, or give it a lot of gas. There's no tranny codes. Call me crazy I would swear the first time it happens each day i can smell something. Could be my imagination. Any ideas?

 

first guess: bad catalytic converter........

 

I've been thinking it sounds a little loud or louder but don't have much to compare too though since i just bought it. Would that throw an emissions code if it were bad or not?

 

if it were bad it may throw a code, I would run it hard for a while and see if the cat glows from beneath

 

Might be unrelated, the car runs at or slightly above 170 degrees, seems odd to me.
The cat going bad is something i haven't heard yet but I definately see that with smell and all. I've also heard it could be a bad coil, maf sensor, or at worst a failing tranny solenoid or t.c.

 

That doesn't sound too off to me, the cats go bad all the time honestly, wouldn't be a solenoid if it's just randomly in the middle of the powerband in 1st or 2nd gear at 35 mph so you don't have to worry about that.

If it was a coil it would be more consistent, not just when warmed up.

MAF Sensor could also be an issue but i'd check the cat first, you can check to see if the MAF is dirty, you can clean it with some MAF cleaner

 

Well I took it to my companies chevy store, they couldn't get it to do anything, no codes, they claim the cat and maf sensor are ok too. Guess i'm gonna have to find a time when it's doing it and try to bring it back before it stops. Got to drive an 09 Si sedan for a loaner so i don't feel too bad

 

So it started up again today, this time i really tried to pay attention to the tach as i'm driving to see what it's doing. Basically at any speed below 50 what happens is you'll be driving at 15 grand, give it a touch of gas to maintain speed and it'll shoot to 2 grand and then instantly drop back down to 15 and jerk when it does it. Now it's not as bad as it was before, and also it's starting up again when my gas is low, which seems like a trend, probably unrelated though. Ideas? Vacuum leak? I had a lot of condensation on oil cap when i bought it maybe a bad pcv?

 

It wouldn't hurt to check for vacuum leaks. Have you given the car a tune up ever?

 

I'm changing the fuel filter today whether it's the problem or not it needs to be done. I'll go from there I guess