'91 100 rough engine shut off

samanthac02 · 05-13-2012, 06:08 PM

my 1991 Audi 100 is shutting off rough, not every time, and I don't know why. I turn the key, remove it and the engine rumbles out one or two more revolutions then stops, reminds me of stalling a standard. It doesn't happen all the time and I can't seem to find any correlations to anything when it does happen.

Only other problems I'm having are needs a new IAC valve, rough/idle and dies and it's starting to look like I need a new alternator, starting hard and dash lights getting dimmer.

Could it be the IAC valve too, is it normal for this model, something more sinister?

This is my first Audi and I'm loving it
Thanks for your responses!

yodasfro · 05-13-2012, 07:46 PM

The running on after shut down you are describing is known as dieseling.
It could be caused by a leaking fuel injector or injectors. The injectors could also be contributing to your idling problem. It could also be the ISV as described try unplugging it and see if the car still does the same thing. You can clean the idle stabilizer valve(ISV)with carb cleaner and then lubricate it with WD-40. You should also check all the hoses for vacuum leaks. The staring hard could also be the fuel injectors. A tune up, new plugs >wires> cap> and rotor may be helpful too. Dash lights getting dimmer hard to say what you are describing. But if they are flickering it could be the voltage regulator in the alt. much cheaper than a whole new alternator. Of course make sure the belt is good tight and check to see if it is charging with a multimeter.

Kneale Brownson · 05-14-2012, 05:07 AM

Check alternator output at both the front and the battery. You COULD have a corroded "splice" in the line from front to back. Splice is under the carpeting in the passenger footwell.

I use throttle body cleaner on ISVs. It includes the lube you'd get by using brake cleaner and following up with WD40.

samanthac02 · 05-15-2012, 10:04 AM

I had already cleaned the IAC valve with carburetor cleaner and tested it unplugged but hadn't lubed it with WD-40 so I did that this morning and checked the alternator, it's putting out a pretty weak charge but the belt seems good. I think I'll take care of these two problems and then look into the fuel injectors.

Thanks for the responses, I had no ideas about what would be making it shut off rough and now I have somewhere to start.

one5k · 05-15-2012, 10:30 AM

i had a bad ignition switch causing a similar issue. when i pulled it out it was cracked

05-13-2012, 07:46 PM	#2
yodasfro AudiWorld Super User Garage is empty, add now Join Date: Mar 2005 Location: CT Posts: 2,400	The running on after shut down you are describing is known as dieseling. It could be caused by a leaking fuel injector or injectors. The injectors could also be contributing to your idling problem. It could also be the ISV as described try unplugging it and see if the car still does the same thing. You can clean the idle stabilizer valve(ISV)with carb cleaner and then lubricate it with WD-40. You should also check all the hoses for vacuum leaks. The staring hard could also be the fuel injectors. A tune up, new plugs >wires> cap> and rotor may be helpful too. Dash lights getting dimmer hard to say what you are describing. But if they are flickering it could be the voltage regulator in the alt. much cheaper than a whole new alternator. Of course make sure the belt is good tight and check to see if it is charging with a multimeter. __________________ Austin 92 urs4 91 200 20v 90 90q 20v 88 5ktq avant Last edited by yodasfro; 05-13-2012 at 07:51 PM.

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05-14-2012, 05:07 AM	#3
Kneale Brownson AudiWorld Super User Garage is empty, add now Join Date: Apr 2003 Location: Full-time Coloradoan now Posts: 3,365	Check alternator output at both the front and the battery. You COULD have a corroded "splice" in the line from front to back. Splice is under the carpeting in the passenger footwell. I use throttle body cleaner on ISVs. It includes the lube you'd get by using brake cleaner and following up with WD40.

05-15-2012, 10:04 AM	#4
samanthac02 AudiWorld Newcomer 1991 Audi 100 Join Date: May 2012 Posts: 2	I had already cleaned the IAC valve with carburetor cleaner and tested it unplugged but hadn't lubed it with WD-40 so I did that this morning and checked the alternator, it's putting out a pretty weak charge but the belt seems good. I think I'll take care of these two problems and then look into the fuel injectors. Thanks for the responses, I had no ideas about what would be making it shut off rough and now I have somewhere to start.

05-15-2012, 10:30 AM	#5
one5k Audiworld Junior Member 1988 Audi 5000 Join Date: Mar 2008 Posts: 81	i had a bad ignition switch causing a similar issue. when i pulled it out it was cracked