O.T. - 1990 VW Jetta idling issue

Good morning, all.

I have a 1990 VW Jetta GL (gas) with 160000 miles. The car belonged to my dad who passed away last year and it sat in the garage for about 18 months. I am trying to fix it up and sell it (to drive or for parts).

Problem: when I start it, it runs rough, and it gets worse as the engine warms up. After a while, the idle starts getting erratic and eventually the engine stalls. The other strange thing is that the catalytic converter and part of the muffler pipe towards the back start glowing cherry-red.

I made sure to put some fresh gas and some "dry gas / injector cleaner" in the tank. I checked the distributor, plugs, wires, coil, etc. - all OK. I vacuumed out whatever debris the mice brought in to the air pathway. I took off the cat and tried to clean it out with an air compressor. There does not SEEM to be an obstruction anywhere. I even tried to adjust the idle up a little.

Before I put it out there as a parts car, I was wondering if anyone had any other ideas. Thanks in advance.

To keep this tractor-related, I used my Ford 2910 to push it into the barn...

Look in the tailpipe to see if mice made a nest inside Sounds like a obstruction someplace.

I would check for an EGR issue, then pull and clean the throttle body. My daughters corolla had a rough idle and there was carbon in there.

Also check for a vacuum leak somewhere in the system.

Check fuel rail pressure, sounds like bad regulator over fueling and the excess fuel is burning in the cat.

Catalytic converter clogged?

What happens if you ran it without the cat? Would make noise, but might narrow the problem.

Vacuum leak will typically make it idle fast.

Check for a cracked plastic dipstick tube, it messes with pcv system.

Look it over for any vacuum leaks or crankcase air leaks, and the rubber/plastic duct between the throttle body and air filter. Since it's been sitting, could be dry rot or mouse chewed, look in the unusual places too.

Also look over the wiring harnesses, same thing, chewed or corroded. Might try disconnecting the battery, let the computer start over.

I'm thinking something is making raw fuel into the catalytic converter, I'd check ignition and plugs first.

Hot cat is to much fuel. Over pressure, dirty Mas flow sensor, coolant temp sensor, altitude sensor. cold start injector open. Etc. Should be a one stop repair, if diagnosed. Jim

You certainly got enough wrong answers and short answers.
1) The fellows that suggested too much fuel are most likely RIGHT. That is the primary reason for a catalytic converter to overheat. The catalyst is actually there to finish completing combustion of the fuel that the engine has not completed. If the engine is running too rich, it will overload the catalyst.
2) Whatever someone did to their Toyota or neon 5 years ago has NO RELEVANCE to your problem today. Too lean of a mixture will cause idling problems, but will NOT cause a catalyst to overheat. Vacuum leaks typically cause a lean mixture that will generally NOT overheat the catalyst.
3) As to cleaning the throttle body - CHECK with the service manual. Some throttle bodies are NOT to be cleaned. For example, Fords since 1991 have throttle bodies that will be damaged by cleaning, and have warning stickers on them about it.

Janicholson had the right answer as to where to start. Also look into a ruptured diaphragm in the fuel pressure regulator. It is a smatt device that looks like a small canister on the fuel rail with a vacuum line going to it. Check it by taking the vacuum line off and looking for wet fuel at that point. It should be DRY.

Good luck!