Idle Up and Down

quattro4ks · 04-07-2009, 06:47 AM

My 1989 100 CS quattro has been in the garage all winter while i removed rust and repaired other things and now at idle, only when hot, the engine rpm just goes up and down. While its warming up it doesn't do it but i suspect as soon as the Cold start valve turns off, the idle just goes from normal to 1200rpm continuously. Someone suggested that maybe the Fuel Pressure Regulator might be the problem. I unplug it and the car idles at 1800-2000rpm. Unplugging the Idle valve does not do anything. Other than this problem, the car runs fine. Is there a way to check the pressure regulator or maybe someone else has had this problem with the 2.3L inline 5?

audi-driver1126 · 09-08-2010, 08:51 PM

i know this is an old post, but i have been looking for a solution to a similar problem on my 1987 4000S

this is what it does

#1 engine turns over fine but struggles to fire, or doesnt fire at all

#2 if the engine decides to start the idle is very low and goes from 500 rpms to about 1200 rpms repetedly

#3 unless the engine is at about 90 on the temp gauge the car struggles to rev and backfires

#4 once warm it runs smoothly and nicly just as it should

maybe its a related problem i dont know

quattro4ks · 09-15-2010, 04:08 PM

Ok so I finally found the problem....The wires to the Idle Control Valve were broken, well one was and i fixed 'em. Then it was just a matter of the mixture adjustment on the fuel distributor and she has been workink fine for a year now, other than the starters that keep failing (picture me lying under the car once a month hammering on the starter to get it to make contact). Even my mechanics can't believe it still runs...Well winter here we come!

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09-08-2010, 08:51 PM	#2
audi-driver1126 AudiWorld Member 1987 Audi 4000 My Garage Join Date: Jan 2010 Location: Vancouver island Canada Posts: 340	i know this is an old post, but i have been looking for a solution to a similar problem on my 1987 4000S this is what it does #1 engine turns over fine but struggles to fire, or doesnt fire at all #2 if the engine decides to start the idle is very low and goes from 500 rpms to about 1200 rpms repetedly #3 unless the engine is at about 90 on the temp gauge the car struggles to rev and backfires #4 once warm it runs smoothly and nicly just as it should maybe its a related problem i dont know

09-15-2010, 04:08 PM	#3
quattro4ks AudiWorld Newcomer Garage is empty, add now Join Date: Apr 2009 Posts: 2	Ok so I finally found the problem....The wires to the Idle Control Valve were broken, well one was and i fixed 'em. Then it was just a matter of the mixture adjustment on the fuel distributor and she has been workink fine for a year now, other than the starters that keep failing (picture me lying under the car once a month hammering on the starter to get it to make contact). Even my mechanics can't believe it still runs...Well winter here we come!