Posts: 758
Joined: 3/9/2004 From: Swamplands of NJ Status: offline
If the car is able to idle normally, hot or cold I doubt that it is dirty throttle valve. Can you start the car with part throttle or WOT only? When you press the pedal all the way you engage the WOT microswitch on the throttle body, this tells the computer to operate in the “open loop” mode bypassing some of the circuits. The 0.010” clearance gap rule may not apply to modern engines. Quite often the throttle valve is supposed close completely. There might be a separate idle port and maybe even a secondary idle control bypass. Check the air bypass circuit and the idle control valve as it is known to stick with time.
Offramp, when the engine is hot it will only start at WOT. Infact it starts prefectly at WOT. When the car is cold however, it starts great without touching the gas at all. -Matt
Posts: 758
Joined: 3/9/2004 From: Swamplands of NJ Status: offline
Since your car starts cold and WOT when hot this could be due to problem with engine temperature sensor. A missing signal could fool the ECU into thinking that the engine is cold and dump too much fuel. Check the connector for corrosion and verify that the sensor works within range. A new sensor is about $40.
When you get your manual try to pull some codes off of the ECU. There should be a procedure for doing it and you could do it without the expensive VAG tool. Do a search on the web and I am sure you will find some information and how to make a test light.
That does seem likely that the engine is dumping toom much fuel in on hot start up. I believe WOT turns off all the injectors, is that right? If so then I see what you're saying. Turning off all the injectors would keep it from flooding which seems to be what's happening, that's why when it finally starts, it blows out so much smoke. As if it's running rich...
Can you tell me where the engine temp sensor is? I know on some cars it threads right into the coolant passage on the lower intake manifold... But I'm not sure where it is on this car.
Can't wait till my manual arrives so that I can look these questions up!
I realized that the only way i finally get the car to start when hot is to put the accelerator all the way to the floor when cranking. So, I just started doing that first. Instead of trying to start the car the normal way first, now I just start it with the pedal all the way down everytime when it's hot. The car starts perfectly when hot everytime when I put the pedal to the floor, so this is what I do now. I'd love to actually fix the problem, but I don't feel like spending about 70 dollars an hour to have my local Audi dealer find the problem.
On a side note... It has recently gotten cold here (upstate New York). When I go out first thing in the mourning it's about 30 degrees out, and I have a hard time getting the car to start. When it does start it runs very rough and sometimes stalls out.
Before it got cold here the car started great 1st thing in the mourning. I never had to give it any gas or anything when the engine was cold. But now the car is giving me problems starting when very cold (30 degrees) Any ideas? Is there a "cold start injector" on this car that may not be working? It's a 1992 Audi 100 2.8 V6.
Any suggestions would be appreciated!!
Thanks alot,
-Matt
< Message edited by 1992audi4life100 -- 10/11/2005 7:10:26 AM >
I am speaking from the point of view of my 1988 Audi 90, 4 cylinder, non-quattro. Appologies in advance as I am not sure if this applies to your particular model, BUT...
OK, I am betting that for some reason, your cold start injector (only active while cranking, and engine cold/cool) is active when hot as well. The cold start injector is located coming out at an angle on the intake manifold (my engine). To test this theory, when the engine is hot, before starting, disconnect the connector to this injector. If it starts fine - bingo, then you must determine WHY it is operating when it should not (engine hot).
It is controlled by the ECU, inconjunction with an engine temp sensor/thermo switch (my car).
I am currently working on the reverse problem - my cold start injector NEVER fires, but the injector itself works fine. I am just about to start replacing temp sensors, will keep you informed...
Posts: 1561
Joined: 8/24/2005 From: Brooklyn, NY Status: offline
I have some sort of same problem or even something smaller like syndrom or even smaller behavior. when the engine cold and fully hot it takes a sec to start up. I mean its harder to start when hot or cold that when its warm or child a little. not as you though. it takes about double time that when warm. wark 1 sec and it starts, cold or hot it takes 3 sec of cranking to start. I would recomend using siries of diagnostics to find out the problem. using lamps and testers cheking when the CSI is working and more.
How about if anyone says your millivoltage, square waves and the like do not explain all there is to these machines?
F'r instance, "well, you don't have the signal to shoot the CSI."
As of the last post, it has gotten down to about 30 F, and it will not start. That indicates that the CSI is disfunctional.
These cars are some of the best starting cars in the world.
I have written this before, once upon a time, my coworkers and I decided to go out to try to start our vehicles, because it was sub zero, the first vehicle, a Mercury, took over half an hour and several cans of ether to get to run, the second car, a Chevrolet Citation, same, the 3rd, I said I am going to my own car, an Audi 5000S Turbo, they went to the next car, a pontiac Fiero, another half hour or more to start.
My own Audi 5000S, Turbo, fired instantly. Drove over to them, they at least got to warm their hands.
You don't think you might just be going a little too deep, maybe so deep into the woods, you can't see the trees?
Evidently we are a little less smart than you, we don't go by sine waves nor square waves, nor millivolts. Hell, I don't know if Bentley's does.
If you are trying to impress anybody, you have, I just don't know whom it might be. Not me. Get your hands dirty, pal.
"How about if anyone says your millivoltage, square waves and the like do not explain all there is to these machines? F'r instance, "well, you don't have the signal to shoot the CSI." As of the last post, it has gotten down to about 30 F, and it will not start. That indicates that the CSI is disfunctional. " - I agree, as I indicated. For example, I removed my CSI, tested it by supplying the correct voltage to it, noted its spray pattern etc. Then I measured the signal (when cold and when hot) to the CSI - none.
"These cars are some of the best starting cars in the world. I have written this before, once upon a time, my coworkers and I decided to go out to try to start our vehicles, because it was sub zero, the first vehicle, a Mercury, took over half an hour and several cans of ether to get to run, the second car, a Chevrolet Citation, same, the 3rd, I said I am going to my own car, an Audi 5000S Turbo, they went to the next car, a pontiac Fiero, another half hour or more to start. My own Audi 5000S, Turbo, fired instantly. Drove over to them, they at least got to warm their hands. " - Nice story George, "heart warming" (forgive the bad pun)
"You don't think you might just be going a little too deep, maybe so deep into the woods, you can't see the trees? " - No, simply applying effective diagnostic approaches. In doing so, I have reduced the possible causes to likely sensor failure.
"Evidently we are a little less smart than you, we don't go by sine waves nor square waves, nor millivolts. Hell, I don't know if Bentley's does. If you are trying to impress anybody, you have, I just don't know whom it might be. Not me. Get your hands dirty, pal. " - George, having a bad day? My references to electrical diagnostics were supplied with the sole purpose of providing as much information as possible for anyone and everyone, which is one of the main purposes of forums such as these. True, my 34 years of experience as an electrical engineer causes me to describe and diagnose more from that experience base. At no time, and in no way have I the slightest interest in "impressing" anybody, just sharing knowledge - George, if I was that "smart", why would I be here asking questions, sharing results? Yes, Bentley's manual does touch on millivolts, ohms, basic electrical diagnostic tools, and other members of the forum have found such references useful. As far as "getting my hands dirty", it is one of my favorite things. I have been rebuilding cars and motorcycles for most of my 56 years of life - dirty is good! Anyhow, no sweat, have a good day!
Ian
Cheers,
George
< Message edited by whimorris -- 10/21/2005 12:41:04 PM >
You're right. It's just that most of us don't have scopes and the like. To get sine waves and the like would require us to go pay the 70 an hour mentioned above, which we're trying not to have to do.
Some things are in mv and R values. Those we can check with a Radio Shack digital multimeter.
As far as this entire thread, I relaized a few up that I may be speaking on a car and engine I have no experience with. A V6, and as to the injectors being dropped out at WOT, sounds as though they are electronic injectors.
My remark, that Offramp must have misread, too, was about the airplate, not the throttle plates, the butterflies. Sounds to me like my remark was totally off, there is no airplate.
I have to leave this one alone, or get a V6 for my next car. I still do read a lot on these cars, if I do find anything pertinent, I'll post, but here I am out of my depth. Hell, I don't even know if the V6 has cold start valve, or valves, one per bank.
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RE: trouble starting when engine is hot - 
RE: trouble starting when engine is hot - 
