Throttle Response
 

Starting a new thread on this...

2003 C4S
52k miles
Manual

So I have a lag in throttle response that I cannot seem to rectify. Looking for any thoughts on this.

The issue is, I need to rev RPMs up to around 2500 or more to ensure the car will not stall out from every stop. Seems to happen when its cold and hot, at all times.

Recently I have had a new clutch and new MAF, new plugs, new AOS and more installed. Smoke test(s) and consequential vacuum leaks repaired. There is less than 100 miles on it all. The air cleaner is new and fresh (note, cold air intake).

I noticed when I pull the plug on the MAF, the problem goes away! The initial clutch engagement and acceleration are exactly what I would expect. However, after a mile or two, the car starts to run terribly and I must shut off and reinstall the MAF plug.

As soon as I do, the problem re-appears.

What suggestions do you have? I was thinking coil pack(s) but I think the MAF test eliminates that potential.

Thanks in advance!

Insure you have the correct MAF sensor, try your old 1 if you have it. Clean throttle body...

Is it andrect replacement clutch or a single mass, light weight one?

If the symptoms appeared after the work was done them something was upset/disturbed. If this is the case then I'd take the car back where the work was done and have the symptoms diagnosed.

With no CEL and no misfire error codes I don't suspect coils, unless it is possible the coils were not connected to the plugs right or the coil connection at the wiring harness is not secure. Since the plugs were changed the coils could just not be installed/connected properly. While I would expect this to cause misfires and turn on the CEL and log misfire error codes maybe not.

I do not know when the symptoms first appeared but that cold air intake raises a red flag especially if the symptoms appeared concurrent with the CAI going on.

If the intake is not right air flow past/actually through the MAF and past the hot film sensor can be upset and the MAF can get confused, so to speak.

Adaptation values get out of whack. If this were happening you could see this by looking the short term fuel trims as the engine is acting up.

However, that the symptoms appear with the MAF disconnected kind of lets the CAI off the hook. However, I just can't help but distrust these since there's no colder air anywhere but where the stock intake is located. A CAI really can only deliver cooler air if the intake system was insulated to reduce the amount of heating the intake air gets from the manifold warming up from the hot engine compartment air. In short I believe this CAI business is bunk, but if you're happy...

Anyhow, fuel supply and pressure have to be considered, along with (longer shot "bad gas"). (Did you put some diesel in the tank?)

Since the engine was worked a fuel line might have gotten damaged/pinched or the fuel filter is just bad, though that MY may not have a serviceable fuel filter, the filter being a part of the fuel pump.

You probably should have an OBD2 code read/data viewer/logger to monitor various engine sensor/derived values while the engine is running ok and when it is not for a clue as to what is going on.

There could be two problems, too. For instance the MAF may be bad even though new (or you could have the wrong MAF or a substandard MAF) and there's another problem that causes the same or nearly the same symptom to appear when the MAF is disconnected.

Oh, you can try to recalibrate the E-gas. Disconnect the battery. Be sure to follow the proper battery disconnect steps. Then reconnect the battery and then recalibrate the E-Gas.

This might be in your owners manual but for some cars it is with the foot off the gas pedal turn the key to on. Do not attempt to start the engine.

Leave your foot off the pedal.

Leave the key in the on position 60 seconds. Turn the key off. Wait 10 seconds. Start the engine.

Window limits will have to be reset as well.

Wrong maf installed?

With the blower on that thing, who knows what the fuel map looks like. Honestly either get it re-flashed by the manufacturer or turn it back to stock.

Went back and checked and didn't see any mention of a SC but if that's the case then I agree with you.

https://rennlist.com/forums/996-foru...asy-on-me.html

With the maf unplugged, the ecu will switch to the default map that uses the expected values of the airflow and will generally be rich (ie so you don't fry ****).

So I would venture a guess and say that that whatever fuel map is on the car right now is garbage.

Aftermarket, used or defective MAF may cause this.

I've found only a new genuine Porsche/Bosch MAF to work as it was designed.

Thanks for the feedback! Excellent. My apologies for not mentioning the SC.

This issue has been since I bought the car about a month ago. I was hoping the vacuum leak fixes and new MAF would cure the issue. The issues are improved, but not resolved.

I just got a CEL tonight as I pulled in the garage, P0442 - a fuel vapor leak in the EVAP control system (Gas cap???) I have seen this before. Re-seated the gas cap and seems to be ok for a while. Could this be the culprit?

I expect my Durametric in the mail this week - is there a specific test I should run, or things to look for regarding this?

I think my next step is to take a short drive to TPC Racing (manufacturer of the SC) in Maryland to have them troubleshoot. I spoke to them and they gave me a few suggestions which I am trying now.

But still seems interesting to me that the problem almost goes away when the MAF is disco'd. Suggests to me that the MAF is functioning because removing it I get the opposite.... Where the start from stop is near perfect, as I would expect, but all other performance is gone.

Also the MAF is the exact part number that is called for from Porsche. is a Bosche ($311).

I hate to get rid of the SC because other than this issue, it is very driveable and frankly is amazing fun and sounds very cool/different. Though, I'm not that stubborn that I would consider removing it too if need be.

Who can do a fuel map flash? Dealer - Maybe a local Porsche tuner?

Things clearing up when the MAF is disconnected is an "old" trick for verifying that the MAF is bad. If things get better when the MAF is disconnected, something's wrong with the MAF or how the MAF is installed.

Forgive me if I'm overstepping my bounds, but from reading this and your original thread, you have thrown a great deal of money at this car in hopes that something would stick. Verifying that the blower is working right with TPC should have been the first thing to try. Defer to the people who should be able to verify how the car ought to perform with the supercharger installed.

Since a blower stuffs more air into the motor than the good lord intended, is the OEM MAF the right part for use with the TPC kit? I would expect over-voltage or other input the car doesn't understand, since the volume of air being ingested is drastically different than what the ECU would expect with a n/a 996. Air is half of the fuel-air mix - if the car can't figure out how much air is being stuffed into the manifold, the AFR is going to be crap. Crappy AFR is a great way to ventilate one's block with extra holes - the kid I sold my blown Tiburon to decided to strap a big-bore throttle body onto it a month after I sold it to him but didn't bother retuning it. The subsequent lean-out resulted in lots of shrapnel where rods once were.

I guess what I'm saying in a roundabout way is that (a) the blower and ancillary parts would be the prime suspect for me, and (b) I wouldn't even think about WOT until TPC or a competent speed shop (which is NOT synonymous with a Porsche dealer or Porsche indy, unless they're known to be handy with aftermarket forced induction) has blessed the install and your tune.

...and if you decide to get rid of that blower kit, dibs. :)

sd_boxter - good stuff, understood.

However, as I understand the basics of a SC, I am learning slowly the nuances of this specific SC. Namely, TPC gave me a few suggestions:

The MAF is right after the coned air filter and prior to the TB.. The MAF is brand new (5 days old) and I have seen an improvement (50%) in response and start up immediately. I spoke with the manufacturer of the SC (TPC Racing) and they had several suggestions:

1) Unplug the MAF completely. Drive around the neighborhood a couple miles etc, and note any differences.

So there I stop, but are other suggestions from them are below. My initial notation is that the problem is FIXED! But with caveats:

a. The starts from 1st gear seem to be what I would expect. Smooth(er) pedal response, clutch engaged like any other car I have driven and I feel more confident about lower RPM engagement.

b. Right away, from start up I get CELs saying ABS and PSM failed. Expected some codes - no problem.

c. Car driving in neighborhood ok - starts from "stop" signs warrant what I would consider PERFECT clutch ratio to throttle response.

d. 5 minutes in: idle is becoming an issue.

e. 8 minutes in: Lots of stange idle, low RPM thrusts.

Pull off road - shut engine off. 30 min later, reconnect MAF, small CEL and I am back to the regular behavior = my inital complaint.

SO....

TPC Supercharger tech told me a few things on this the other day - RE: the new MAF and a lack of throttle response.

*) He mentioned in later iterations of their design that they use a 2004 Audi S4 throttle Body tube (with OEM Bosch 996 MAF).
*) That the "exact position" of said TB tube form S4 allowed a more specific and optimal "position" of the MAF, based on the SC/MAF needs. Would that make sense to any of you?

2) Restrict the airflow from the cone filter slightly.
He mentioned that the 2004 Audi S4 TB intake tube has a "screen" in it. That was enough to restrict airflow to make the MAF happy. Thus, they started using it. Results were consistently positive so this was an on-going-forward strategy.

My result on attempt of this restriction shows no difference. I may try buying a throttle body tube from an S4.

3) Next, the two additional fuel injectors into the SC. He said to test them by pulling them out, turning the ignition on to see if there were leaks prior to starting. If so = fail and replace. (Trying this today)

4) Lastly, He said there was a separate and additional computer controlling the SC that could be failing. Really said that would be a last resort and that the previous 3 would usually resolve things.

So - any other thoughts are appreciated. I have a tuner near my house I am going to call tomorrow. Since they work on 80% of the Porsche and Audi cars for the local track here, I am guessing they may have some experience.

Thanks again for your help here!

Couple of things...

What the TPC tech told you regarding the Audi TB tube and his mention about the more optimal position fits right in with a point I made about the air flow past/through the MAF.

The screen is not to restrict air flow but to improve air flow. In the past there have been those that have removed these -- in other cars -- to "increase" air flow only to have the engine react in a negative manner. The screen is not to keep snow out, leaves out, or block air flow, but to improve air flow. Hot film MAF are very good at measuring air mass and are about as trouble free a device as you could hope but they need the air flow just right. As the system comes from the factory it is right. But if you mess with it you can certainly make it wrong.

That the results of your putting this screen back in may be mixed due to the other problems. The screen alone may not be able to deal with the excessive air turbulence arising from the shorter intake tube.

Before you have a custom tune or flash done you need to be sure all of the issues under your control are dealt with. The tuner will be pulling his hair out trying to come up with a tune for a sick engine. In fact, I would expect the tuner to want to experience the car before any tuning is done to ensure for himself the car is operating ok before wasting his time and your money on what would likely prove to be a futile effort to get a improved tune.

Excellent advice!!! I will follow. I found a "fairly" cheap tube (with screen and MAF already on it) on ebay. Though I dont expect this MAF would work on my car, right?

This is my next step this week.