My S4 seems slow - any ideas?

[mrditto]

First of all, let me introduce myself. I am an S4 Avant driver in West Yorkshire.

I have had the car for over a year and over that period the performance has been fine. About 2 weeks ago, the car just started to feel slow. There was a lack of urgency away from the lights, and a general lack of power higher up the rev range. The car felt gutless above 4500 rpm and accelerating from 60 in third took an eternity. Also, fuel consumption during this time has gone crap. I only got 175 miles from a full tank where I would usually get 240+ miles.

The car only runs on Optimax - and I do not use any fuel additives.

Does anyone out there have any ideas what the problem might be? I want my old S4 back!!

Thanks

Great board BTW

[Paul-RS]

MAF fault maybe?

leaking/split/loose hoses?

im sure the lads will be along shortly...

[mrditto]

I don't have a VAG COM - how do I diagnose a MAF fault?

I don't think it is a split hose (although this is purely speculative) because when I fill the car up with petrol, even before turning on the ignition, the DIS, which for the last year, would suggest a range of 270 miles, now only suggest a range of 210 miles - almost like it knows there is a problem.

[Dippy]

Welcome to RS246.

I'm sure that you've gathered by now that the K03 turbos on the S4 are not exactly the strongest around. So if you have any problem which can affect the turbos, you need to get it sorted quickly. So as you're not in a position to do much self diagnosis (to be honest, if you don't have VAG-COM then you really don't have much hope), I suggest that you get it to an Audi dealer or an Audi tuner asap.

You already believe that the car is running rich, which at least means it won't be overheating at the exhaust which is good. But unburnt fuel can cause other problems.

It could be the MAF, although typically this fails by reading too low, causing the engine to run lean. The more likely reason for running rich is an air leak, and the TBB the most likely culprit.

Your deduction about the DIS is a red herring. The DIS simply takes a set of recent mpg calculations and projects it. Yes 210 is very low so you are definitely getting a very low mpg. And yes this can be because of an air leak.

To check the TBB you need top remove it. Unless you are confident in doing this you need to take it to someone who is.

[Nige_RS4]

If you haven't got access to a VAG-COM and don't want to be ripped off by dealers, I suggest you start by replacing the parts that fail most often (and are the cheapest). Replacing the TBB (throttle body boot - Y-shaped black hose at the front of the engine) with a SAMCO one from AMD and a set of 710N bypass valves (uprated) from VAGPARTS. Both are an easy DIY fit and will cost less than £70. If you are still having problems after replacing these, then you need to check your MAF - they are £200+, so worth finding out if it is faulty before you replace it. Possibly worth putting a boost gauge on for a couple fo days to see what's happening there too - you may be in limp mode ?

BTW - I had similar problems with power loss above 4500rpm and it was traced to a fault MAF (with no errors codes being thrown), but only a dealer/VAG-COM will tell you for sure what's wrong with your motor.

Good luck [img]images/graemlins/thumbs.gif[/img]