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MBC question...

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mbc question
1K views 14 replies 5 participants last post by  Steve in Chicago 
#1 ·
Hey everybody,

I just had one quick question that maybe someone who has tried it can answer.

I just put on a MBC nothing fancy just a valve behind the n75 and everything was working ok then I started getting a misfire and now my throttle body is going haywire and wont calibrate properly on the vag-com it just errors out. I was wondering if the boost controller is the cause maybe it couldn't handle the extra boost? Its an ebay aftermarket throttle body I think I paid 80-90 for it. The car is a 99 passat AEB 1.8t 193k miles.

Thanks for the help.

Matt

Also the misfire is on cylinder two.
 
#2 ·
Misfire, cylinder 2, on an AEB almost always means that the ICM is dying--get the cheap Huco version, unless you have deep pockets.

If you have a stored DTC (your misfire), VCDS can't run the throttle body alignment. So replace the ICM first.

Are you chipped? And how did you plumb in the MBC--series or parallel to the N75?
 
#4 ·
Hey,

No chip although I wouldn't mind getting one. The car is stock. I put a valve basically inbetween the waste gate and n75 valve. Gezz I hate those ICM pieces of junk. Can I put a fan on it or something?! Would the icm cause the tb to go bad though?

Thanks

Matt
 
#3 ·
IMHO a manual boost controller is rarely the best idea, but I'm not sure how it would cause throttle body and misfire problems. The obvious check is to remove it and see if things go back to normal. But first, try a new ignition control module. AEB, misfire, and cylinder #2 fairly screams a failing ICM.
 
#5 ·
Hey,

Ya I was just trying to get a little more boost out of her not go crazy with it. It was working actually really good until the misfire and tb problems started. I actually want to say the tb problems started before I did the MBC. It seemed like at very little throttle it would jump and stutter then the misfire started. So I will try the icm first and go from there.

Thanks for the help.

Matt
 
#6 ·
Ok, so if you are not chipped or anything, lose the MBC. And if you want more boost, chip it (still leaving the N75 alone). You'll go from 150 to 200 hp--a 33% gain at 50 hp. Unitronic can also flash your ECU, so see if there's a dealer near you. I also think GIAC can flash the AEB's ecu.
 
#7 ·
2.0T ignition coil conversion may be cheaper than replacing your ICM alone.

Also, the AEB stock has TINY injectors, and the safe limits to how much you can boost is incredibly low. How high were you actually boosting? (I trust you have a boost gauge hooked up)

Throttle body is *probably* still okay, but as said, with any DTCs, it can't properly calibrate, so clear them, don't start it, and try again.
 
#10 ·
If you have an eBay throttle body it should always be considered suspect. As should any component you just installed; how long ago did you do so?

No matter what price you get on anything, there's always a cheaper one out there. A $399 tune (like the one from APR) should indeed give you the gains it specifies. There's a lot of research behind it, and a lot of reputation at stake. A "cheaper" option, or a "custom" tune, not so much.
 
#11 ·
I installed the tb along with a bunch of other new parts probably 3-4 months ago. The icm is a huco, after buying a cheap one from ebay and deciding that one was bad but it actually was my spark plugs. I need to re look at the plugs. I doubt the tb is still under warranty. I have my old tb but I accidentally broke a wire inside.

Thanks for the help.
 
#12 ·
Note that the 1.8T is quite picky about spark plugs. Most of the ones they sell you at a generic auto parts store won't work properly, and indeed cause misfires. Unless you have a very good reason not to, always use the factory-recommended plugs. For your car, I believe that's a Bosch FR7LDC+.
 
#14 ·
Ok so I just checked the spark plugs a little while ago before I started replacing a bunch of stuff I didn't need to and low and behold the number two plug had actually blown out. I pulled the plug and the shield or whatever it is around the center conductor had come apart and was just loose inside the plug. So I replaced all the plugs and that fixed the misfire issue. I am assuming the plugs didn't like the extra boost coming in.

The throttle body however I have come to rule that it's bad. I took the intercooler hose off the throttle body and turned the key to the on position. While the key was on I could hear a loud buzz from the throttle body and checked to see if the butterfly was opening and closing and it was doing nothing. Also the vag-com is giving me the basic fault error so hopefully I can get a replacement soon.

Thanks for the help.

Matt
 
#15 ·
What make and model of plugs were in there? What did you replace them with?

The AEB isn't more prone to go into limp mode. Due to it's more primitive array of sensors and fewer controls, it's less likely. That might sound like a good thing but what it means is, if you draw too far outside the lines with your modifications, the management system is less able to act as a safety net for your mistakes. Instead of auto-correcting or going into protection, it'll keep going even if it tears itself up in the process. I wonder if you were detonating hard enough to shatter that #2 plug ceramic?

First get it running proper, then find a tune. The AEB has no immobilizer so a chipped AEB ECM from the classifieds would swap right in. Or price out a Reflect tune. Or see if there are any tuners local to you and shop price. Some tuners only do AEB tunes by soldering on a chip. You don't want that if you can avoid it. You'd rather find someone who will flash the software upgrade into the ECM via the OBDII port.
 
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