I have a 1.8T with a CVT. During the warmer months, the thing idled PERFECTLY. It read about 950 on the tach (although these things are notoriously inaccurate). Since the CVT is effectively in "neutral" when you are stopped, the idle was VERY smooth. But, every now and then, you would hear a relay "click" and the engine would drop 100rpm (to 850 indicated)and would idle rougher (it was not the cooling fan). After a few seconds up to maybe a minute, you would hear "click" again and it would boost back up and idle fine. Did not matter if the engine was warm or cold. Now that it is colder, it runs rough nearly all the time (below 35 degrees - engine warm or cold). But, every once in a great while, it will "click" again and boost back up for several seconds to several minutes to the "smooth idle, 950rpm" behavior. The click is obviously some relay clicking in and out. What could this be? I want the idle to remain smooth (obviously) but I don't want to give the dealer several hundred dollars to likely tell me that this is "normal" because their VAG tool does not read any problems. When I Vag the thing, I get "intermittent miss, cyl 4" (plug - coil pack?) and "intermittent miss - multiple cylinders. The "rough idle" I get does not feel like a cylinder miss. It feels like an idel air controller on the fritz. The plugs have about 25k on them.

Any clues?

 

these engines are notorious for cold start misfires. I have seen it a ton. One thing that you could be hearing on cold start up is your secondary air pump. It pumps oxygen into the exhaust to heat it up at a quicker rate, to get the oxygen sensor in closed loop. However they do have a cold start misfire issue, it could be several things, i know there is technical bulliten issued by audi to solve the cold start misfire via software update as long as it applys to your vehicle. The issue could possibly be solved by an injection service(cleaning of the intake system and the fuel delivery system, bg makes a decent product). Your throttle body may also be the cause. It takes no more than 10 minutes to take the throttle body off and clean it. good luck.

 

The thing idles slightly rough below 32-35 degrees outside air temperature whether the engine is warm or cold. Above that outside temp, it runs fine whether the engine is warm or cold.

 

Upon further review, the "problem" may actually be related to the cooling fan. I notice that, during warmer weather when the thing idles smoothly, I can hear the cooling fan "winding down" whenever I shut the car off. Sounds like a jet engine spinning down when it is shut off. I thought it might be the turbo spinning down, but I raised the hood and shut it off and saw the cooling fan was the source of the noise. I know that some engine computers boost the idle when the cooling fan(s) come on to stabilize the idle. In cold weather when the thing idles more roughly (and at the 100 or so less RPM), I noticed that there is no noise on shutdown cuz the fan is shut off. In warmer weather when it may temporarily drop down and idle rougher (10 seconds or so), the relay "click" I hear may actually be the cooling fan shutting OFF.

I'm not sure what the operating parameters are for the cooling fan(s). Most VWs have one fan connected to the thermo sensor in the radiator or somewhere in the coolant circuit. And, the second fan is usually connected to the A/C. The usually only come on when the temp of the coolant gets high from idling in hot weather, or you turn on the A/C. I have no idea why it would be on all the time from 32-35 on up.

I had some dealer service work done the other day and I was given a new A4 for a loaner. It was cold out and it also idled crappy, exactly like mine when it is cold. I would have LOVED to pull the new one inside a heated garage for a while to see if the warmup would also make it idle better. When mine is inside a heated garage where it has been overnight, it will idle fine when started and pulled out right up until the outside air temperature on the dash reads about 32 or so. Then, it is back to its crap idle. Yes, this temperature thing appears to be directly related to the INDICATED temp on the dash readout and NOT the actual instant temp outside. It takes these Audi temp gauges several minutes to adjust to a significant change in actual outside temp. So, it is not that the engine is sucking in cold or warm air, it starts to happen (or stops happenning) when the TEMP GAUGE says it is cold or warm.

Any thought on these theories?
Thanks,
Mike

 

audi a 4 1.8t engine amb 2003

intermittent problem, cold about 60 f engine starts and die once , sometimes twice, up to 5 times ,then runs ok, except that when hot at idle after a long time , rpm will flutter very intermittent and only yellow triangle sort of letter ''a '' which is esp or traction control will come on for a few seconds or stays on, sometimes engine will die, no mil , then later mil on , starts up right away , great stable idle , great acceleration, car has only 40,000 miles, 4 new coils from dealer last year, scan with vag com several times, misfires random or on each cyl, 16486 mass air flow too low, 16490 , manifold absolute pressure implausible signal,
18265 in autobox load signal error from ecu, sometimes also get codes 17519 o2 sensor regulation system too lean, if i clear codes, the car behaves perfect for 2 up to 4 or 5 days, then all these codes come back mostly system too lean, cannot find any vacuum leak, put a new bosch maf , there was also p 1128, new coolant sensor green was already green , so cheap , put a new one, new suction pump jet, , i should monitor fuel pressure, and get a smoke machine, since some days it is perfect , so it is not a case of deposit on valves, and sludge, the software update i think is if you have a constant misfire on start up, it seems that everytime i clear all the codes the car is ok for 2 to 4 days, i check throttle actuator, it was not dirty, i cleaned it anyway, did throttle adaptation with success same for autobox, fuel trim most of the time are below 5 per cent for stft and ltft, lambda close to 1
but when bad idle, stft goes up to 20 percent positive, my fuel pressure gauge is broken, will get a new one next week, this is not a typical pattern failure for this amb engine 1.8t or i am deadly wrong , any advice appreciated ...