[MatrixE93]

I was getting random misfires, eventually causing the car to go into limp mode every time it reached operating temperature. I am at 30K miles now and I knew the previous owner had a tune on it, so rather than play around with troubleshooting, I decided to tackle the obvious stuff all at once:
-cleaned intake valves using crushed walnut shells
-installed 6 ignition coils (replaced Bosch with Bosch)
-installed 6 spark plugs (replaced NGK with Bosch)
-new air filter
-my car has the Cobb AP installed and has been on map 0 since it started misfiring a couple months ago.

Here is a before and after of the valves:



After putting everything back together, when I start the car it immediately starts revving between 1000 and 1500 rpm and the throttle is completely unresponsive. View My Video of this happening

I am getting the following codes:

P2CF9 - A throttle potentiometer
P2CFA - Throttle potentiometer 2
P2D09 - Throttle control - faulty air (group error for TPS)
P2CFB - Choke adaptation value

So far, I have tried:
-throttle adaption reset procedure
-reflashing map 0 from the Cobb AP
-disconnecting the battery overnight
-removing and reinstalling the airbox and chargepipe, double-checking all sensors are plugged in.
-checking all the 30 amp fuses in the glovebox

The next thing on my list would be to completely uninstall the Cobb AP. I welcome any other suggestions, I am running out of ideas and there doesn't seem to be many posts with the codes I am getting.

[NOTM3]

did you gap the plugs properly?

[MatrixE93]

Originally Posted by NOTM3

did you gap the plugs properly?

No, I wasn't aware they needed gapped. I thought all plugs are pre-gapped these days and the Bentley service manual doesn't make any mention of having to adjust the gap. I did install Bosch model ZGR6STE2 so they should already be the correct specification for the N54.

[mankytron]

Seems like something is not plugged back in or has been bumped loose by the r and r of the intake.

[Bme30]

something sounds unplugged.

[NOTM3]

my bad i read it backwards i thought u said u added ngk, yea bosh don't need to be gapped, something may be unplugged , I'm just not sure what, when I did mine i didn't have an issue

[kfrazie1]

My guess would be maybe a damaged throttle position sensor?

[MatrixE93]

Originally Posted by kfrazie1

My guess would be maybe a damaged throttle position sensor?

I did open the throttle plate by hand a couple times while cleaning it. Could that have damaged anything?

[DuDai]

I used to get that exact same thing on cold starts. Cold being anything below -30C. Would let it run for about 2-3 minutes, shut it off, restart it, and ran perfect. Never got a single code ever. Put the jb4 on and never have had the issue since. No idea. Very weird. I'm curious to know what happens.

[peter91118]

Originally Posted by MatrixE93

I did open the throttle plate by hand a couple times while cleaning it. Could that have damaged anything?

You might have sent current back into the motor drivers on the circuit board. I wouldn't be surprised if your throttle body was toast.

[kfrazie1]

I've moved the throttle by hand before too and never had problems after. I believe they disconnect the Throttle Position Sensor when they remove the manifold. If not done correctly It can be damaged. Double check it wasn't screwed up.

[pwr hungry]

Did you make sure to reconnect both map sensors and both vacuum hard lines going to the throttle body?

[cwarren]

has to be a connection issue ive done at least 10 walnut blast jobs and i always clean the throttle body hence moving the plate and never had an issue .

[dbjb]

Originally Posted by pwr hungry

Did you make sure to reconnect both map sensors and both vacuum hard lines going to the throttle body?

I'm thinking loose vacuum line. I cut the very end for a fresh connection.

[Tiago@VRSF]

Check the vacuum line and the TPS harness.

The NGK's need to be gapped, Bosch plugs are pre-gapped.

[Tzu]

Thats indicitive of either the throttle body connection or vacuum line to the throttle. Likely was not plugged back in. Do a DME reset after.

[dannygee90]

Most likely something isnt plugged in. Check all sensors and lines. Might have missed something. Good luck.

[Tony@vargasturbotech]

This will happen if you forget to plug in the TB, which is the big square plug on the bottom, very easy to not get seated all the way. A vacuum line will cause a lumpy idle but will not remove all throttle control. Meaning its a plug not a vacuum line. Check all your plugs including both map sensors. After you insure they are all plugged in, go into your Cobb AP and reset the ECU.

[shawntech]

TPS isn't plugged in

[MatrixE93]

Well don't I feel stupid. TB was not plugged in correctly.

Thanks for all of your replies!

[shawntech]

now that that's resolved, any noticeable difference after the port cleaning? I'm at 93k and mine is being done Monday. I have a stumble/shake @ cold idle that goes away after a few minutes but no misfire codes and runs perfect warmed up, no faults stored.

Mine haven't ever been done and surely much worse than yours pictured, but we'll see Monday!

[MatrixE93]

It is noticibly smoother. No stumbling at idle on cold starts, no more jerky acceleration, hasn't misfired yet.

I did get a p29dc code "cylinder injection shutdown" once the engine warmed up today. I had gotten that code a few times before but thought it was because the dme detected too many misfires. No misfires codes though this time. It happened in fourth gear getting onto the highway as soon as I gave it about 70% throttle.

How likely is it that the HPFP is starting to fail?