I own a 1990 745 turbo with 286,000kms on it. Ever since summer, the car's run rough when cold. Idles very low. (Idle is normal when the engine is warm) And I can smell an extremely strong rotten egg smell of the cataletic converter at stoplights even when I've been driving conservatively.
This would indicate to me that there is unburnt fuel coming out the exhaust.
I think the low idle when the engine's cold and the cat working overtime are related as they happened at the same time. I might add, the car's getting AWFUL gas milage.. seems to have plenty of power, though.

I thought I may of melted a valve last summer when I pushed the engine extremely hard in very hot weather. (maintained 15psi boost for several minutes during extremely hot weather), But I just did a compression check and all 4 cylinders are all reading 162-170psi. That all seems normal.. I'm relieved, but that doesn't solve the problem. The plugs looked perfect when I pulled them out to do the compression test.

One of the first things I did was borrow my dad's fuel mixture readout that connects to the oxygen sensor lead to check the mixture. The mixture is right where it should be. I think maybe the oxygen sensor is bad. But I can't afford to replace it at the moment.

Any ideas? I'm desperate for help soon as I have to take the car through emissions testing soon in order to get insurance.

Thanks!

I have never heard of having to smog test before getting insurance, can you explain this?
As a police officer I deal with many uninsured drivers and know the importance of insurance however I can find nothing in the lawbooks that requires a smog test, only a test to get renewals on plates.
MN used to have a smog test (CO+HC/NOx) however that went away and you had a pass/fail only.

No insurance in MN gets you a 30 day suspension, revocation of plates and/or $700 fine. Future offenses get you jailtime and revocation

As for the cat, it's toast

Badge 988

Bad fuel economy usually means rich mixture. See the FAQ for information on rich mixtures. One thing I have noticed is that gasoline varies by brand: when I use the local Kum&Crap convenience grade, the throttle body and injectors plug up and the car smells like rotten eggs. Amoco reverses this. First try changing gasoline brands and putting a bottle of Techron in the tank.

Rotten egg smell doesn't mean rich mixture. It does usually indicate a bad cat though, and if the engine previously had problems, then it could have damaged the substrate, even melted it. Cat's are not cheap, but it's not the end of the world either- $120 or so, depending on where you get them. I would definitely get the right one, rather than the "generic" ones that Meinass will weld to your car and screw up the rest of the exhaust.

I've never heard of needing the test to get insurance.... you get insurance FIRST, which allows you to drive the car to get a test, to get permanent registration or renew your old one. Insurance companies don't give a #### whether you pass emissions or personally cause a bad air quality day with your car.
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Rob Bareiss, New London CT ::: 86 244DL, 87 244DL, 88 744GLE, 91 244: 808K total