Poor Acceleration

[IrY100Fan]

Hi Everyone,

I'm new to this forum and hoping somebody can shed some light on my problem. (Before I try going to the dealer.)

Lead -up...
I was driving my 2004 Audi S4 (91k, Auto) on a back road a few days ago and had someone in a older Honda CR-V behind me that was upset that I was only doing 10 over the posted speed limit of 25. He decided to pass me on a two lane road and I thought "no you don't" so I put my foot to the floor. (Yeah I know, poor/unsafe judgment on my part.) Well the CR-V passed me without any problems.

For the past few months I kept thinking my car seems slower than I remember but I thought it was just my imagination. (When I own a car for a few years, I tend to get "used to" the feel of it.) So a family member and I went to a empty 4-lane highway and I "drag raced" my car and a 2003 Subaru Outback (4-cyl, 160k, Auto) from the stop light. I couldn't keep up with the Subaru. Now I'm really disappointed.

Other details...
I have no "Check Engine" light on and my generic OBD-II reader says that are no pending error codes or stored codes. I have noticed a dramatic decrease in fuel economy over the last few months. (I used to get 17-18 to work and 22-23 on highway, now I get 11 to work and cannot get past 18 on the highway.) Also, I have been slowly loosing coolant over the past month. (I had to put about a half-gallon in. I don't know where it's going, but it doesn't seem to be getting into the oil and there's no white smoke so I wasn't immediately worried about it.)

I am hoping that the collective intelligence of this board may be able to shed some light on my dilemma before I have to take it to an expert or dealer. I can try and supply more information if needed.

I appreciate everyone's input on this issue.

Thanks.

[bakedcorn]

Hi...

Have you performed a tune-up lately i.e. spark plug replaced, oil change, motor flush, air filter replaced, spark plugs cleaned, gapped etc? You may also have carbon build up on the valves, pistons, plugs which could potentially lead to diminished power. Engine compression could also be a culprit here.

I'd do the simple / basic items first i.e spark plugs, oil flush, air filter followed up by a fuel additive solution to clean out the injectors and valves.

I'm no pro or pretend to be but I figure the logical route to take is usually the best solution.

[LINDW4LL]

LOL. This is brutal.

Sorry, OP.

[Glennb]

i am ot sure whether or notthe 2004 s4 has a throttle cable or if it is a signal to the engine from the throttle.
If it is a signal throttle than there are rare cases when the signal is lost and it can interfere with the acceleration.
your best bet is to take it to a mechaic so that they can reset the signal. (this is only if your throttle is an electronic connetion to the engine.

for a throttle cable it could be that it is loose. this happens alot in old muscle cars. you can simply tie som zipties around the trottle cable to make up for the slack in it, but this is only if you are on a budget haha.

good luck!

[QIKRNU]

Your car does not have a throttle cable. It is all electronic.

[JayDog747]

Hi...

Have you performed a tune-up lately i.e. spark plug replaced, oil change, motor flush, air filter replaced, spark plugs cleaned, gapped etc? You may also have carbon build up on the valves, pistons, plugs which could potentially lead to diminished power. Engine compression could also be a culprit here.

I'd do the simple / basic items first i.e spark plugs, oil flush, air filter followed up by a fuel additive solution to clean out the injectors and valves.

I'm no pro or pretend to be but I figure the logical route to take is usually the best solution.

You will not get carbon build up, they are NOT direct injection engines.

OP, You should perform the 95k service, plugs, filters, oil, brake fluid change if its been 2 years. Consider replacing the coil packs. I recommend BG 44K fuel cleaner, it goes in the gas tank and works well. You will have to get under the car to find the coolant leak. If you don't know if the transmission fluid has ever been changed, change it. Along with the rear diff, front diff and center diff.

[LINDW4LL]

Sorry for my unhelpful earlier post.

If the coolant isn't leaking, it must be burning. A head gasket leak causing low compression is what comes to mind. I know you say you don't see smoke or milky oil, but it's an easy place to start.

I'd start with a compression test and see what you find. Something has to be seriously wrong for you to be losing so much power. My only other thought would be badly clogged catalytic converters or a timing issue, but the latter would throw codes.

[SprintBlueWorld]

Start with air and fuel filters followed by fuel injector cleaner. Tune up spark plugs coilpacks, early s4 models had bad coilpacks that were revised many times. Clogged cats could also be an issue as mentioned above. Piggy em out and the car will breath much better. If you really want to get wild rebuild your fuel injectors.

[IrY100Fan]

Everyone,

Thanks for the fast replies.

Here's what has been done...
* Changed the spark plugs and air filter at about the 60k mark. (Had a rough idle at the time but that fixed it.)
* I change the oil about every 5000 miles or so. (Changed it about 1000 miles ago. Everything looked normal with the used oil. The dipstick isn't showing any indication of oil contamination so far.)
* I run a bottle of Chevron Techron about every 6-8 fill-ups.

Here's what I'll do when it stops raining around here...
* Check the air filter. (I do live in a very dusty area.)
* Change the spark plugs. (They're pretty cheap plus I'll take a look at the old ones and see if anythings look suspicious.)
* Check compression. (A buddy of mine has a compression tester so I can check that while I'm doing the spark plugs. I hope it's not a head gasket but that would explain the dwindling coolant level. I doubt burning a half-gallon of coolant over a month would be noticeable in the exhaust.)

I have never changed any fluids except for the oil. Pretty sure the brake fluid needs to be changed but that certainly isn't causing my trouble. The coolant in the expansion tank still looks really clean but I'm sure it's do for a change.

Coil packs did run through my mind but I wasn't sure what the symptoms would be. (FYI: My sticker in the driver's door jam says "03/04" so I'm guessing it's a early production '04 car.) Does anybody know how to determine if it's and original or "upgraded/replaced" coil pack?

Also, I never thought of clogged cats. The sound of the car is very different from when I bought it. I remember hearing the "overrun burble" if you were hard on the gas and then quickly let off. Lately my car just sounds like a leaf blower.

What astounds me is that with this much performance loss that the car isn't throwing a "Check Engine" light.

I post back when I have some more details. In the meantime, thanks for the help.

And,
No problem having a chuckle at my expense. That's what I get for trying to be just as much of a jerk as the guy in the CR-V.

[xhackerekx]

make sure u have v8 engine under the hood.
subaru and crv smoke u each of this slow cars no have more like 180hp .

[badger.]

With that much of a performance hit and the loss of the burble sounds like it is either fuel or exhaust related. My $ is on exhaust. If your gas mileage is that shitty I doubt it's a fuel delivery issue

Do you have an exhaust leak? Maybe one of the flex joints let go. Idk if that could cause such a serious loss or not. That would be pretty easy to hear though.

My bet is a clogged cat, I know when that happened on my old car it absolutely killed performance. This seems like the most probable given all the info so far. Although you'd think it would throw a code for O2 sensor...

Will be interesting to hear what it is! Good luck

[SprintBlueWorld]

Latest revision on coilpacks is "T"

[SuperAvant]

My money might be on coil packs.

[Tugboatguy]

Quick test for coolant is to have a freind follow behind you with his heating fan on hi, if your burning coolant he'll smell it.
Your car is an auto, is it shifting properly?
Is the intake flapper stuck in the wrong position?
"Sounds like a leaf blower" vacuum leak? Broken / disconnected vac hose?,

[jr1415us]

Coolant loss aside, low power can result if the intake manifold changeover flap isn't functioning as intended. Search around this forum, you'll find plenty on the subject.