Although I am a nueb on this site I have been working with this car for over 2 years. I did a search and found a few similar problems but no solution. I will try to be brief.

Problem : No heat from vents at idle, increase rpm and heat blasts out. ..simple enough

Atempts at repair.

1 Repaced thermostat , water pump, and coolant, bled coolant umpteen times with no results.
2. Replace cap from coolant syatem, replace heater hoses from fire wall to engine ( what a freakin nightmare )
3. Actually removed entire dash and replaced heater core and checked flapper boxes, everything functioning correctly and new core installed. Same problem.
4. Bled coolant sytem again.
5. Used thermal laser and found that coolant temp going into core just not hot enough , increasd RPM and coolant line temp increased by about 20 degrees.
6. Engine gains and manintains normal temp on instrument panel. cAn actually indicate a lower temp on the highway and be blasting out the heat , and a higher temp while idling yet blow cold.
Checked head gasket for leaks, no pulsing at the expansion tank , engine runs strong, no coolant usage at all, and each time I bleed no air comes out.
7. Bled by overfilling expansion tank untill fluid came out of bleed hole , caped off bleed screw and returned expansion tank to normal level.

The Audi 90 has no heat control valve, just straight from the engine to the firewall.

Other than this problem the car is SOLID, but it is undrivable in Canadian winters in bumper to bumper traffic. Occupants will freeze to death. CAr has to be parked for half a year.

HAs anyone experianced or has a resolution to this or is this a design flaw to which ther is no resolution ?

Thanks in advance

PS since this is my first post thought I would atatch a pic. I have practically rebuilt this car from scratch and this is the only problem that eludes me.

 

I actually did that to my car. I had a problem that becouse I had too much flow through my heater core I got a freaking heat waive during winter. So I took a plug made a small hole in it, and pluged my heater core. Now I have warm air on idle and hot air just giving light gas.

Other problem was that my engine keeps overheating, and that gave more flow through the rad. Now no higher that 95C.

check that the tubes that go to the heater core are in fact not bended or cloged. If you used water there that might have created problem. Use a small long wire and poke the system through. By inserting the wire into the heater core tubes and uncloginf anything there might be. A heave gauge wire should do that.
Also checj the heater core if there anything in the path of the flow.

 

To me it still sounds like a bad thermostat. Did you check the thermostat in a pot of boiling water? Just because it is new it doesn't mean squat. Other problems could be with blocked passages or a problem with the water pump.

 

Thanks for the response guys .... and just to recap since I was not clear on a couple of points.

I replaced the heater core and both hoses that run to the heater core, one comes from the coolant pipes that come from the head and the other goes to the return pipe to the water pump.

I replaced both the water pump and the thermostat. the original thermostat I tested as fine. I don't think it is an engine heating problem given that the engine comes up to temp fine and regulates fine. If I am running along the highway the temp is actually in the 80 -90 range and will melt you if you out it on full blast. idling the engine goes up past 90 say 90 - 95 or so yet blows feakin freezing. I do believe it has to be a blockage somewhere but I am running out of places.
Do you guys have ample heat at idle. ?

Also what was tha about the plug and what does it do ?

I almost want to belive that the pump isn't running fast enough at idle to draw the fluid through the core, like there is a path of least reisitane somewhere else. This one has me totally stumped.

On a somewhat realted note do I have to pull the engine or intake manifold to check the pipes that my hoses fasten to ?

 

If the pump and thermostat are OK then it has to be the climate control. On my 91 100Q I had a similar problem but it was totally random. The problem was due to servo flap that was worn out, instead of blowing air through the heater core it was bypassing it and blowing outside air. The controller has a diagnostic feature, when it is blowing cold air try reading the codes.

 

Hi TheIceman,
did you already solve the problem?

I have exactly the same problem with my 1988 Audi 90 (5 cyl, 2000 ccm).
I've also changed water pump, heater core, thermostat and hoses.

Still the same :-( On idle it blows cold air.

Does anyone have a solution, please?

THANX
buzz

 

-- double post. removed --
buzz

 

Hello! My A6 has just started with the same problem! Did you ever solve the problem? Just read something about the servo blowing air which ive noticed mine giving off air once i turn the car off!

 

+1 to 0fframp: did you test AC errors? Any temp flap related failures?

 

Well Guys I have still not resolved the problem .. The 90 does not have climate control . it does not even have a heat control valve. I am hearing of more and more cars with this issue but very few have answers. I used my thermal laser and see a definite decrease in temp from run to idle .... get this i did discover something important .. if I take the hose off the heater core at idle .. nothing comes out .. ther is hardly any flow .. if you touch the gas it spews out ... sort of like the coolant is by passing the heater core .... and guess what .. my Audi A6 with the same engine is now doing the same thing .. there is just not enough heat to regulate .. I am suspecting some type of blockage in the block of the engine .. the hard coolant pipes or the pipe that runs under the intake manifold .. I have allmost given up on this problem now as I am out of things to check or change .. but i do know it is a flow issue ...