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Audi 5000: 1984-1988, 100, 200: 1989-1991 (C3) Help: Audi 100/NF/88 Instable idle, fault code 2121, but idle switch is OK


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Last Post: Aug 26, 2006 4:38 PM Last Post By: erikw
erikw

Posts: 10
Registered: 03/06/06
Help: Audi 100/NF/88 Instable idle, fault code 2121, but idle switch is OK
Posted: Mar 26, 2006 9:22 AM
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Hi,

Audi 100 (5000) from 1988 with 2.3E NF engine is having problems.
Since a month there are many problems with the CIS-E-III fuel injection. It started with the mixture that became so rich that plugs chocked in black tar, and car stopped. After that i cleaned intake manifold, and replaced all seals in intake system. Air filter, plugs, oil, temperature reader, ignition runner, idle-switch and OXS-sensor (lambda) have been replaced. Air distributor has been adjusted and seems to run fine and smoothly. Fuel distributor has been cleaned.
Following can be observed:
1) Engine starts fine in the morning, although exhaust stinks on gas.
2) It idles fine, until temperature = 50C.
3) When engine is getting warmer, idle starts oscilating between 1000-1200 in a high frequency (vroom-vroom-vroom) with short intervals. Idle speed is not a moment stable.
4) Fault code = 2121.... I tried two used sets of used idle switches before a new one was installed, same result.
5) Measuring idle switch on throttle body shows expected results, switch closes when throttle is moved.

Although 2121 is shown, i doubt if it is idle switch related.
What are other sympthoms:
1) Idle Stabilisation Valve is not used, when disconnected nothing changes, idle keeps oscilating as before.
2) Current to Idle Stabilisation Valve (ISV) = 35 mA. It should be 500 mA ??. On the connector to the ISV 13V is present.
3) Checked wiring from Control Unit to ISV wire (green/black), connection seems to be fine.
4) When i connect ISV to battery, it opens, and car starts oscilating between 1000-1600 in same short intervals.
5) Car drives very nice, takes gas well, and does not seem to have lost power.
6) Fuel consumption is 30% higher then before problems started showing.

Does somebody have a clue where to look now ?. All help is very much appreciated, i do not know what to do anymore. Spent $400,- on parts, 50+ hrs. in debugging and cleaning everything, but result is still bad.

Thanks in advance.

Erik
Fixit

Posts: 866
Registered: 08/31/04
Re: Help: Audi 100/NF/88 Instable idle, fault code 2121, but idle switch is OK
Posted: Mar 26, 2006 1:43 PM   in response to: erikw in response to: erikw
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If there is no difference when you disconnect the ISV then maybe the crankcase breather system is clogged up.

You should clean the system. see my post on the subject here....

http://tech.bentleypublishers.com/thread.jspa?threadID=19093&messageID=176376#176376
erikw

Posts: 10
Registered: 03/06/06
Re: Help: Audi 100/NF/88 Instable idle, fault code 2121, but idle switch is
Posted: Mar 30, 2006 3:23 PM   in response to: Fixit in response to: Fixit
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Hi,

Thx. for the answer, i read your excellent article on this.
I had cleaned the tubes for a few weeks, and based on your answer, rechecked if everything was fine. Only little stuff was in there, mainly rust particles from the metal pipe.

There was no change, car behaves the same. Also i changed injector inserts O-rings and seals... no change. I will open a new post on this, since a month i am busy with the car. I slowly get the feeling that it out smarted me.

Greetings from Holland,

Erik
Fixerdude

Posts: 9
Registered: 01/09/05
Re: Help: Audi 100/NF/88 Instable idle, fault code 2121, but idle switch is
Posted: Apr 6, 2006 11:39 PM   in response to: erikw in response to: erikw
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Hi Erik! I had similiar problems with rpm dropping off at 1200rpm and surgeing methodically and rapidly on my 89 Audi 100 Quattro NF CIS-E3. It would only move under it's own power without jerking if I kept it under 1200rpm. Never tested fault codes, but I seem to have it fixed. New spark plugs, wires, distributor cap, and rotor didn't seem to improve condition. New idle stabilizer valve (under $300 US) showed first sign of improvement, got it up to 2000rpm until warm and started surgeing again at 1200rpm. Then I got a new 110 amp alternator (under $300 US) and it's been running great ever since. What I've learned is that with this type of problem it is most important to have a very good battery and alternator as all the electrical gadgets (fuel pump, radiator fan, climate control, etc.) take alot of power and if it doesn't get it, it won't run right. The alternator and battery output is easiest for me to check, too. It helps to have such a great group of people on this site who share! Good Luck, Bryan
erikw

Posts: 10
Registered: 03/06/06
Re: Help: Audi 100/NF/88 Instable idle, fault code 2121, but idle switch is
Posted: Apr 11, 2006 5:38 PM   in response to: Fixerdude in response to: Fixerdude
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Hi Bryan,

Thx very much for the help. All parts you mentioned (and some more) were changed, except the idle stabilizer valve and the alternator.

When alternator is bad, can this problem being diagosed ?.

Erik

nize

Posts: 71
Registered: 04/07/06
Re: Help: Audi 100/NF/88 Instable idle, fault code 2121, but idle switch is
Posted: Apr 11, 2006 6:32 PM   in response to: erikw in response to: erikw
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maybe it could be the fuel injectors themselves? when was the last time the injectors were professionally cleaned and flow-matched?
ErnieBee

Posts: 157
Registered: 10/04/05
Re: Help: Audi 100/NF/88 Instable idle, fault code 2121, but idle switch is
Posted: Apr 27, 2006 1:35 AM   in response to: erikw in response to: erikw
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Erik,
I just went thru something similar. Be sure your throttle butterfly plate can close ALL THE WAY! It's the 5mm adjuster screw with 8mm lock nut, on the right side of TB as seen from front of car. If it can't close, air gets past it and idle control no longer works.

After I did that (and many of the things you also did, too) I finally got control of idle speed with the screw on the top front of the throttle body. Before allowing the throttle plate to fully close, I could screw that all the way in or out and no change. Note: Prev. owner had broken the factory yellow-paint seal, to reset this - wrongly.

But I still had the oscillating rpm between 1100 & 1300 or so: What fixed it for me was to swap out the ISV, which you have done several times. Could it be your plug to the ISV has a broken wire under the rubber boot? Or corroded contacts? Or a leaky hose to it?

Anyway, that's what finally got mine working right. I had to readjust CO (mixture) but then I had got that completely screwed up chasing the rough idle problem the wrong way, at the beginning. Now my 200 idles at 850 rpm, solid.

I also hear that the single coolant temp sensor on top by the rad hose, affects this; it sends a signal to the idle control unit that's mounted behind the panel in driver's footwell (left, vertical), which in turn controls the ISV. This temp sensor body can get corroded and be no longer making contact with the block, so if it reads correctly on your meter, remove it and clean both threads so it's got bare-metal contact. And replace, of course, if it's not reading correctly. Also the wire spade contact on top could be correded, or the wire broken somewhere?

And I guess the elec. control unit in the footwell elec. panel,as mentioned above, can also go bad, just by itself. Dunno, but I've heard that.

Hope this gives you areas to look at, hope you find it.
Ernie
erikw

Posts: 10
Registered: 03/06/06
Re: Help: Audi 100/NF/88 Instable idle, fault code 2121, but idle switch is
Posted: Aug 17, 2006 4:56 PM   in response to: ErnieBee in response to: ErnieBee
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Hi Audi-Fans,

Again thx for all the advice.

Now we are 4 months further, and the story has not ended. Being tired of the instable idle, i replaced throttle body by one from a NG engine which has this magic piece of technology... A manual idle adjustment screw !!. Since then idle does not oscilate anymore.

Although the annoying idle oscilation is gone, car still does not run great. In the morning it first idles on 1-2 cylinders, the rest gradually jumps in after 1 mile drive. When started warm same story.. breaking with left foot to keep it running.

After 1 mile car runs fine, and has stable idle. However, the idle is stable at varying levels between 550-850, screw set to +-850 rpm. Each time when going from driving into idle, the idle maybe stable at 550-850.

Problem should be solved before winter, otherwise car will not start in the morning.

Does anybody have a clue what is ?. All help is very much appreciated.

Thx in advance.

Greetings from Holland.

Erik
audiqv8

Posts: 211
Registered: 05/21/04
Re: Help: Audi 100/NF/88 Instable idle, fault code 2121, but idle switch is
Posted: Aug 17, 2006 9:53 PM   in response to: erikw in response to: erikw
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DTC code can be caused by the throttle cable being out of adjustment. See Bentley manual D2-320-1 for description. Also see Bentley manual in adjusting throttle cable.

The fault can be generate either by the ICU (ignition control unit) or FIC (fuel injection control unit).

i replaced throttle body by one from a NG engine which has this magic piece of technology... A manual idle adjustment screw !!.

Kind of hard for anyone to help if you start modifying it from stock, since the ICU and FIC are trying to control the idle and also the fuel/air mixture base on operating information being supplied by the sensors.
erikw

Posts: 10
Registered: 03/06/06
Re: Help: Audi 100/NF/88 Instable idle, fault code 2121, but idle switch is
Posted: Aug 20, 2006 6:01 PM   in response to: audiqv8 in response to: audiqv8
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Hi,

Thx for your answer. I put NG throttle body because nothing kept the enigine from oscilating idle 900-1200 rpm.
Spent since February this year 100+ hours on solving bad idling, had my mechanic looking at it, changed airflow meter (used), changed ECU (used), changed Lambda sensor (new), cleaned fuel distribuor, changed fuel filter, cleaned whole air intake system, had CO checked, replaced injector inserts and O-rings, valve cover seals, spark plugs, replaced idle switch for a brand new one, changed cold start valve (used), Checked on vacuum leaks, Posted in this and German sites (got no clear clue how to get rid of 2121), Sacrificed chicken and goats on the hood, but nothing helped.

With the NG body, at least the idle is controllable.
The car is now driveble, but cold and warm starts are not really a smooth.

Greetings,

Erik
audiqv8

Posts: 211
Registered: 05/21/04
Re: Help: Audi 100/NF/88 Instable idle, fault code 2121, but idle switch is
Posted: Aug 20, 2006 6:17 PM   in response to: erikw in response to: erikw
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Seems as though you replaced everything except for the FIC (Fuel Injection Control) unit. The FIC communicates with the ICU (Ignition Control Unit). I don't think that your engine have an ECU since it isn't a turbo.

I would check the FIC at this point.
erikw

Posts: 10
Registered: 03/06/06
Re: Help: Audi 100/NF/88 Instable idle, fault code 2121, but idle switch is
Posted: Aug 26, 2006 4:38 PM   in response to: audiqv8 in response to: audiqv8
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Hi,

Sorry, my mistake, the FIC was replaced, i just mixed them up. You are right, everything was replaced, except the injectors.... Last week i found out that three were bad, based on an amateur test: Take them out, put them in heavy gas (kerosine), put 8 bar on them. Due to the gas, a grey spray pattern will be visible. Three were blowing sideways in a flat pattern, two had nice straight cone-shaped pattern. Based on that i concluded that three injectors were bad, and another $350,- were due for five new ones.

Anyway, this week i sold the moneypit to a Russian, who will export it to Kazachstan (where ever that may be).

Now i drive around in my faithful 85 quantum gl5, which does not have this horrible KE-III but a simple K-Jetronic.

Thanks very much for the advice.

Erik

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