Audi 100 1990 NF engine cold start issues

[GabrielB]

Hello everyone. This is my 1st thread here. I fixed an oil pressure problem not long ago (was a bad sensor) and now I have problems with the cold start. Problem started a while ago and I thought was because of a defective ICV. I replaced the ICV ( have 2 spares) and nothing. Engine starts and idles fine for a few seconds, and stalls if I don't hit the gas. Even pressing the gas pedal, engine runs rough and sputters, and I can smell gasoline out of the exhaust. After 1 or 2 minutes, when it warms up, everything goes back to normal. No more smell, good idle, good response. I checked for vacuum leaks (replaced all small hoses and tested the whole intake with propane. OK), replaced the valve cover gasket (was "wet" with oil) and intake gaskets, new distributor rotor and cap, new wires and plugs, new OEM high pressure fuel pump, new filters, cleaned throttle body and valves, cleaned airflow sensor, checked WOT and idle switches...I even replaced the dipstick o-ring and the DPR o-rings. Tested voltage feeding ICV (getting full battery voltage) and connectors all around. Tested coolant temperature sensor and readings are falling within factory specs for cold/hot engine. I found that the O2 sensor, instead of fluctuating between 0.2 and 0.9v as it should be, reads only 0.24v most of the time, and changes only between 0.2 and 0.34v (cold and hot, same thing. Tried leaning the mix or adding propane, no change). But I was reading also that the O2 sensor does not "kick in" until the engine is warm, and when the engine is cold it operates on open loop mode, with default settings and without the help of the O2 sensor. If that is correct, then a bad O2 sensor should not have anything to do with my cold stalling problem. Anyone can confirm this? Thanks in advance...

[GabrielB]

OK. After a few weeks chasing the problem, I got it finally nailed. Problem was on the air shrouded system (NF engine, CIS III). The crankcase vent recirculation system put a lot of oil on the intake manifold over the years (I've never cleaned this before). It was awful around the injectors. The injection pattern without the air shroud assistance was horrible. So what I did is I took both parts of the intake manifold out, steam cleaned everything, replaced all gaskets and injectors o-rings and cleaned the injectors. Also I rerouted the hose from the crankcase vent. I took it out of the intake boot ( I don't want oil on my intake anymore), plugged the hole on the intake and put a breather filter at the end of the vent hose. Working beautifully now. Hope this info helps somebody.

[Harinder Singer]

I just cleaned the intake area near MAF sensor and throttle body[two throttles], where the crank case vent connects.

But
[1]. The car behaves different after cleaning the intake area which was quite dirty due to junk coming in from the Cr. Case vent...creating starting problem.The car starts fine now.

The vent from Crank case was loaded with crud, and was cleaned.
The idle rpm now is upto 1200 instead of 750 /800 normal.

The boot input connected to filtered air output, via an annulus vertical throat[connected to fuel injection pump]was also cleaned where a plate moves up with suction[throttle opening] actuating the injection system.

No light to light up the Instrument Cluster. ...irrespective if light switch is on park/full beam/high beam.But the display on Cl. Control shows the temp setting and the LED for econ and other selections.
[The Climate control sometimes turns the heater fan on sometimes not....]
When you turn the parkg lghts on, the display on Climate Control disappears....meaning whatever is supposed to dull the panel light when night[park select], cuts the power to the C Control display.
Also the clock display and the diagnostics display[OK or radio data]...disappears when aprkg light switch is turned on.

All fuses in the fuse box under the hood checked, and are ok.

[2].Old problem: [Going on since 100,000 miles].

As we know the Radiator fan has three speeds.
On AC selection [or Defroster]the first speed comes on, as it should...BUT the fan willnot come on[with AC off...heat on/off], when the coolant temp on the gauge on dash shows the needle past thick bar, nearing vertical. Only going further in temp say 1 o'clock position that the second speed of fan comes on..which is late. Can it be that thermostat is stuck.

The radiator sensor has been changed.

The separate gauge for oil temp still shows near 100 deg C approx...and doesnot move much while the coolant temp gauge moves from say 70 deg C to 100 deg C[the sensor locations being different].

What is wrong electrically in [1] above, and how to fix it,
and what is wrong in [2]...sensor/thermostat what ever ?

Thnx

Swedllander

Country: United States
Make: Audi, Miles 155,000
Model: 100 cs
Year: 1991
Engine: 2.3L/5 cyl

Already Tried:
checked all the fuses... The radiator temp sensor is changed.

[Prospeeder]

Your temp issue could be the thermoswitch in the radiator that controls the fan is bad, and is only allowing the high speed at the higher temp. Thermostat...ehhh no. Radiator could be clogged up too. But it sounds like the fans just coming on late so i would start with the 3 wire thermoswitch at the radiator. They are actually 2 speed fans. Low and High. Thus why the switch has 3 pins, 1 power low, 1 power high, one ground

[Prospeeder]

I would like to add

You said you replaced the switch on the bottom of the radiator for the radiator fan. Your certain it is the right one, you can purchase one speed and higher temp and lower temp ones too. Depending on when they want the fan to come on. Next, the only thing i can think of is the "hot" for the low cicuit on the switch could have an open, or poor connection. There is also a low and high speed radiator fan relay.

[Prospeeder]

About your climate and clock stuff going blank, Sounds like the signal wire (wether they use it as a power or ground) from the light switch to each of those displays has an open. or it could be as simple as the light switch is bad.

[Harinder Singer]

Thnx folks.

I agree, think its the switch or relay for the fan low speed.

[I remember seeing the circuit for III speed...meaning lets say the two speed thermo switch at radiator does go dead total, then a separate engine temp sensor[NOT radiator]...blasts the fan like a jet engine...].

For display...yes it does seem something doesnot send the power[low illumination]to the dash board.

But does anyone understand the idle speed at 1200 rpm...?

[Harinder Singer]

Still fighting with idle speed above 1200...

Several other indicators may be pointers ........that you can review and advise !

The engine stalls when you suddenly deccelerate/brake, obviously the vac in the intake goes down or almost dies....so it seems the idle control system/valve is not functional ...so the idle [and regular] mixture is running rich.

Checked the mpg today...it has dropped from 25 hwy to 19, and city from 19 to 15 for this 2.3L engine...simply disgusting.

So either the MAF sensor, is sensing wrong and thus failing to control the fuel/air ratio...and running it rich may be the cause of fast idle also....possibly.

Besides cleaning the MAF sensor and surrounding area, is there something electrical I can check to confirm that sensor is misbehaving...?

And what exactly is the idle control system...?

[Harinder Singer]

Can any one identify the idle control/stabilizer hardware...?
[in the Audi % cylinder 1991/100].

The prblem with 1200 idle speed has to do with it...since there are several ocassions when you deccelerate, the engine idle[with Xmission in drive], goes down to 500 and then dies.

Thnx

[x19]

Can you back prove to 02 sensor and what are you seeing from 0.2V ~ 0.9? or
If you see the good swing you have to adjust the throttle. x19