Ricey exhaust!

[1rstbmw!]

Alright I've been having some problems with my car. On idle the car sounds like a 350:eek: it drops rpms a little and then climbs back up.The thing is it only does this part of the time but is getting worse.It has a horrible rattle comming from the catalytic converter part of the exhaust. When i go for a "spirted drive", It will hit 3500 RPM and drop 500rpm and climb back up, I think these problems are all related.It is a 98 ti so I know there is a recall for the cat right? Im getting the supersprint resonator so if that is the problem that will solve it, but I would like to go ahead and get the free cat from bmw:biggrin: .
So I guess the question is does this sound like a CAT problem? CEL is on.
Thanks in Advance

[Viper3812]

It probobalby is the cat if the light comes on because of the second sensor back there. Just to let you know if you dont know already, once you put the resonator on the CEL will stay on because of the second sensor.

pm sent.

[1rstbmw!]

Yeah I was pretty sure on that but as long as it doesn't affect performance, I don't mind the light.

[newagecustoms]

This may sound dumb, but you might check your vacuum lines under the hood, mine was doing that awhile back, I found a vacuum line loose under the hood, pluged it back up to where it came from, and the car runs fine now.

[Mendi3]

This may sound dumb, but you might check your vacuum lines under the hood, mine was doing that awhile back, I found a vacuum line loose under the hood, pluged it back up to where it came from, and the car runs fine now.

You are absolutely correct! BMWs are very sensitive with vacuum leaks. I had a very similar problem and it took me a while to discover I had a vacuum leak coming from the brake boost. I replaced the part and the problem went away.
A good way to check for vacuum leaks is to buy a small propane cylinder and with the car running, open the propane cylinder just a bit and run it under the hood everywhere you can. If there is a vacuum leak somewhere you will notice the car will start running smoother. If you remove the propane cylinder it will go back to run rougher.
I hope this helps.

[Calgary98TI]

If you have a 98 with less than 80,000, the cat should still be under warranty. I just had mine replaced in the fall. 8 year 130,000km (80,000mile) warranty on emissions related items. It is worth at least a phone call to the dealer.

Sounds similar the what my car was doing prior to getting the cat replaced.

[1rstbmw!]

I've already replaced some vacume hoses, but I will check for some others .It still doesn't explain the rattle sounds coming from the mid part of the exhaust.

[Tyler]

If you have a 98 with less than 80,000, the cat should still be under warranty. I just had mine replaced in the fall. 8 year 130,000km (80,000mile) warranty on emissions related items. It is worth at least a phone call to the dealer.

Sounds similar the what my car was doing prior to getting the cat replaced.


There was a recall on the cats from a 98 and it's covered under some federal law that i found in our owners manual . I had mine replaced 3 years ago,it was so bad that my car wouldn't go past 45mph on the highway.

[1rstbmw!]

There was a recall on the cats from a 98 and it's covered under some federal law that i found in our owners manual . I had mine replaced 3 years ago,it was so bad that my car wouldn't go past 45mph on the highway.


Did it start off dropping rpm's in a certain spot or just happen in a few days?

[1rstbmw!]

You are absolutely correct! BMWs are very sensitive with vacuum leaks. I had a very similar problem and it took me a while to discover I had a vacuum leak coming from the brake boost. I replaced the part and the problem went away.
A good way to check for vacuum leaks is to buy a small propane cylinder and with the car running, open the propane cylinder just a bit and run it under the hood everywhere you can. If there is a vacuum leak somewhere you will notice the car will start running smoother. If you remove the propane cylinder it will go back to run rougher.
I hope this helps.


Are there any other ways I can figure out where the leak is coming from I'm pretty sure I have a vacuum leak, anyone have a diagram of where all the hoses are?

[J!m]

vacuum hose routing is on the sticker on the left strut tower.