Help CIS-E III expert !! audi 100 88/NF engine gives persistent 2121 and bad idle

My car has gone crazy, and keeps being smarter than me, unwilling to get fixed. Now engine behaves like dr. Jackal and Hyde. Problems: 1) COLDMODE: When started cold, car start fine, runs warm on 800-1000.
When it gets warm, idle gradually drops to 200-300, engine nearly stalls, but mostly catches just in time with flashing dashlights. When driving, it takes gas badly, and hesitates before engine picks up. Engine sounds very hollow when idling, also slight loss of power seems to be present. 2) WARMMODE: When car is started warm, it behaves different. Idle is oscilating fast between 1000-1200. For the rest it runs fine, and takes gas very well. Also no loss of power seems to be present. 3) Generally, car runs very rich. I replaced OXS-sensor, but still it smells on gas, specially when running in COLDMODE. Turning down CO screw only results in unability to restart at all.
Because i don't like breaking with left foot to keep engine alive when car has to stop, i removed ISV connector. Without ISV connector, car shows constant WARMMODE behaviour.
In the last month i changed and cleaned all parts involved in air intake and fuel injection. Fault code 2121 is present, but new idle switch didn't make the problems and fault code go away. Changed parts: 1) Seals of intake pipes. 2) Temp. sensor (black). 3) idle switch. 4) Injector inserts, and o-rings. 5) Plugs/air filter/oil. 6) OXS sensor. 7) Valve conver seal. 8) Fuel pump is 1 yr. old. 9) Changed cold start Valve, original is suspected to leak or not close properly.
Question: I am now at the level where i am desperate. What should i do next ?. All help is very much appreciated.
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that code seems to point to throttle switch. http://www.12v.org/maintenance/dtc.php?code !21
"2121 Closed Throttle Position Switch. Possible Cause Corrective Steps a.. Closed Throttle Position (CTP) switch needs adjustment a.. Throttle valve sticking a.. Floor mat presses on accelerator pedal a.. Accelerator pedal cable needs adjustment a.. Open circuit in wiring to connector A, terminal 9 of ECM a.. Input for CTP in ECM faulty (ECM is faulty) a.. Connector A, terminal 9 of ECM has short circuit to ground a.. Moisture in throttle connector a.. Check CTP output a.. Adjust accelerator pedal cable a.. Repair open/short circuit in wiring
Error is stored if the throttle opening is greater than 7 and the CTP switch is closed for longer than 1 second, or if the CTP switch has not been closed at least once as soon as the engine has been started and there has been a 10 minute drive under 62mph. "
Usually I find that the wires going to the switch break before the plug. Or the throttle is not fully closing. Does your 100 have a secondary throttle plate? Possibly it is stiff and does not fully close.
Do you have the Bentley repair manual? If so you can do a multimeter test from the ECM plug and check out the FI system/sensors/switches.
good luck, dave

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Hi dave,

You ask if throttle does not close well and let pass air into engine although it should be closed ?.
I checked throttle body. connected multimeter to terminals 1-2 of connector, and as soon the throttle is moved little, switch opens. Same holds for full-throttle switch. On the plug ends there is 12V.

I have Bentley manual, and tested cables from ecm plug to terminal, will check again if there is a ground-leak or short.
You have a clue why engine is running in two modes when ISV is connected ?. Sometimes it looks as if ISV tries to regulate engine speeds, but can not hold it because something is out of spec.

Thx very much again.

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REPLIES WITHIN

But if there is a secondary butterfly valve, that 2nd valve could be staying open just a hair creating a problem like you are describing. Sounds like things are good there electrically.

That is why checking from the ECM plug is a good way to find/test out the system electrically. Don't forget that mechanical things can create problems like the throttle body plates, fuel distributor and boot, etc. Does EVERYTHING check out within specs? How is the coolant temperature sensor? How is the fuel pressure? Too much, too little or just right?
That code is pointing you to the throttle body though!! What year is this Audi?
thinking out loud!
--
later,
dave
(One out of many daves)
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One out of many daves schreef:

Throttle body has two plates inside, a big one, and a much smaller one.
To be sure i wil replace it, have another one around. If the plates do not close, then the body is worn out ??, i do not see what can be done about a throttle that does not close well. I replaced original body with one from a NG engine, it looks equivalent, inside it was very nicely polished, and seemed to work fine. On this NG body new idle and full-throttle switches were assembled. I see you point, the original NF body has an extra thicker plate on the small plate, which gives larger closing surface with inside of throttle body. Because the NG body does not have this, air might be passing through the small plate, causing vacuum problems.

Coolant sensor is brand new from audi dealer, haven't checked if it is good. will do. Fuel pressure should be good, first the pump is an original Pierburg less then a year old, second, and that is actually the frustrating part... Car drives like a dream when it is not in idle, takes gas good, and seems to have sufficient power. Since car is not holding back when full throttle is applied at higher speeds, fuel quantity and pressure should be in spec ??, i have no tools for measuring the fuel pressure. Connectors on potentiometer en fuel pressure regulater check ok.

I know, the problems started two months ago, car stopped because it suddenly ran extremely rich, and chocked all plugs in tar. The whole intake system looked as if car was run on coles. Since then i cleaned everything, and replaced all seals, cleaned fuel distributor and checked air distibutor. Everything seemed to be ok, if plunger plate is lifted with fuel pressure, it goes evenly, but heavy. Can fuel distributor be worn out ???

It is a 1988 NF 2.3E, with facelift (new doorhandles). Idle was never as stable as with my simple K-Jetronic 5cylinder quantum (passat) from 1985.

I apreciate your thinking very much, it helps me to get closer to this ghost that is spoiling the pleasure on this great car. So far, actionplan is as follows: 1) Check wires from ecm 2) Replace throttle body, recheck idle switch position 3) Check temp. sensor

You'r the best !.
Erik
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REPLIES WITHIN and edited

WAIT are you saying the full-throttle switch activates as soon as you open the throttle? Shouldn't it activate only at WOT (WIDE OPEN THROTTLE)? Have to check this! ;-)

Corrosion usually causes the throttle plates to slightly stick open here in Chicago. I can usually get them to work properly with some penetrant and elbow grease.

I have not worked on many of your engines so I am not sure if it has a cam sensor or even a crank sensor (Engine Speed Sensor). I would venture to say NO it is not present. Correct me if I am mistaken.

That FPR is electronically controlled and you can monitor current flow with a Digital Volt Ohm Meter AFAIK. I have seen some vehicles run with a bad FPR and some not. Need current to that FPR and I have seen some people mistakenly remove the fuse! 8^o

If the fuel pressure is too high won't that cause more fuel to come out of the injectors? Possibly fuel distributor, but I would not change that yet. Wires to the Oxygen Sensor shorting out can cause a rich mixture

I would check and not replace the TB! ;-)
--
later,
dave
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