Hello,
I just bought a 1998 A4 2.8 NON-quattro from a local lot. I also have a '99 Mercedes SLK230 Kompressor. I know the Audi is not supercharged like the Benz, but it doesn't have nearly the amount of power the benz has. The Audi should have a little more power than the 4 cylinder benz, but it doesnt. Its really weird - when I get on the gas, it pulls strong until about 4000 RPMs, and then it slows way down. It continues to accelerate, but sluggishly, albeit rather smoothly. Smooth in the sense that its not misfiring, but its still kinda chunky accelerating. As long as I stay below 3500-4000 RPMs the engine is very smooth and has decent torque, but, for example, if I'm pulling out in traffic, I step on the gas and it starts to go very quickly, and then hits ~4k and acceleration slows way down. If I keep it floored it will continue to accelerate until ~6000 rpms, and then shift to 2nd gear, at which it regains some power b/c its lower in the RPM band again. The check engine light isn't on, and I know the bulb works b/c it lights up when you turn the key to position 2, but then goes right out when you start the car. I checked the obvious, like the air filter, and its brand spankin new. The car also has just had an oil change, but I don't know about plugs, altough I highly doubt they would be causing this. Any ideas are helpful. Thanks for your help folks.
Daniel

 

Well I beleive in 98 the 2.8 had 190hp how much does your slk have?
Also most 4 bangers powerbands are higher in the rpms where as most 6 banger powerbands are in the mid rpm range Ive never drivn the 2.8 so I couldnt tell yah exactly but its somthing to remember when comparin the two.

 

The SLK has 185hp and ~200ft lbs torque. The thing about the A4 thats weird is that when I'm driving, lets say I'm going 40mph, I step on it and it kicks down to say 3rd gear, ~3500rpm, it GOES, but then I push the gas to the floor, then it'll kick down to 2nd, about ~4500rpm, and then the power decreases. In other words, it has more power when in 3rd gear than after it downshifts to 2nd. I KNOW this shouldnt be, regardless of the peak torque/hp ranges, otherwise why would the transmission downshift at all if the car had less acceleration after the downshift? BTW, I spoke too soon about the Check Engine light. It came on - I went to Autozone and they pulled the codes - it said "Multiple Cylinder Misfire", then "Misfire Cylinder 6", "Misfire Cylinder 4", and finally something about "Mfr. Idle Speed Control Sensor" or something like that. Maybe she just needs new plugs.

 

Yeah those codes explain why you've been having issues with high end hp.

The misfires are critical, they need to be sorted out.
The speed control sensor may be over-sensitive (malfunctioning), thus it would send erroneous info to the ecu; the ecu would then retard the timing whenever the revs get into the high range.

 

Can you explain to me what relation the "Mfr Idle Speed Control Sensor" would have to the computer controlled timing? And is it something I could work on/replace myself? Also, sometimes when I start the car the engine is cold it sounds almost like there is an exhaust leak somewhere. It goes away when the car warms up, but its just sorta a slight rattling/leaking sound coming from right under the passenger compartment. You can only hear it from outside the car, and its pretty quiet, but I wonder if that might have somehting to do with it - especially since the engine pulled misfire codes from only cylinders 4 and 6, which are on the same bank and I assume on the same exhaust route. Thanks for your replies.

 

I don't know if your exhaust sound is directly related to the 4 and 6 misfire; it may be another issue, and it may be minor.
If I'm not mistaken, the sensor may not be shutting off and the info that the ecu gets will cause it to retard the timing. It is not something you can "work on" yourself. If it is bad or going bad, it will need to be replaced.

To be sure, I will double check on this in my Bentley's and get back to you.

 

well if you just bought it Id take it back with codes in hand and tell them they need to sort it out unless youve already had it to long.

 

SlimChriz: I don't think he can do that. It's "...a 1998 A4 2.8 NON-quattro from a local lot."

greaserz: You might want to consider the following tech articles:

Idle Control Valve Tech Article

And this: Throttle Body tech article