Mk4 jetta mass air flow sensor
 

My 99 jetta keeps throwing off the code p1128. Could this be because of my cai? Or do I need to get a new one?

Try cleaning it first. Get a bottle of that mass air sensor cleaner, like at oreilly, napa or any other car parts store. Also, look for any vacuum leaks on that intake booth.
If you do end up needing a new mass air sensor. go to germanautoparts.com. They have good deals on parts for VWs.
Hope this helps. :)

Alright I'll give that a try and see what happens. Hopefully it does just need to be cleaned.

My car also threw the code b0423. I know his is for the body but I'm not sure what exactly for or how to fix it.

What's the year of the Jetta and what size of engine, if i may know??

It's a 1999.5 2.0l aeg. I was doing some research on it and i found that depending on what scan tool is being used it will give different codes. It also said that the b0423 code could also be p1176. Is this correct?

Yes, your correct. That code doesn't even exist, if you look it up starting with the P.
So.. that's the only code.
The code your giving me actually means SAEVAGDescriptionP112817536Long Term Fuel Trim mult., Bank 1 System too Lean
Which it could be lots of things.. You should deff. inspect all the vacuum hoses, specially the braided ones. Check the exhaust for any leaks.
Also, check the secondary air inj. system. I sure hate that system cause is worthless...
The other thing check the fuel pressure. It could also mean that the O2 sensor might be going bad. But, yeah first try cleaning that mass air meter sensor and go from there. I can access alldata. Let me know if you need instructions on anything.

I cleaned the MAF it had a good bit of dirt on it. I also erased the codes on my car and so far the light is staying off. I just hope it stays off.

I agree with you.
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I did clean the maf. It worked good for about a month and a half. However now my car is giving 4 codes this time. P0440, p1582, p0171 and b0423. I did a little research and it looks like they are all pointing to the tb. Is this correct and if so what should I do?

Take a look at the TB and if you see dirt, try to wipe it of with a rug and spray some of that mass air cleaner on it....

P0440 is part of the Evap. system. Have you checked all the hoses for air leaks?? Specially the intake booth??

Ok I'll take a look at the tb. I didn't yet. Thats located right behind the maf correct? I did an oil change about a week ago I did find a loose hose going to the intake manifold. I put a clamp on it. Could that cause the p0440 code?

Yeah, it should be behind it... I know that your air intake is on the right side. That loose hose could have triggered one of the codes.. Mostly the one that has to do with the TB.

The hose that I found was loose was on the left side of the intake manifold. It hooked on right next to the engine block. Could that cause all these codes by any chance? Also I do have an after market exhaust put on. I replaced the downpipe and cat, also the rest of the exhaust. My old cat was competely hollow, could that have caused any of these problems?

It shouldn't cause any problems. I hope there are no exhaust leaks somewhere. Did you install it yourself?

I did do it myself. Would an exhaust leak cause these problems? If so would a leak anywhere in the exhaust system cause it or would it just be a leak before the last o2 sensor?

A leak before the cat. could trigger a code, because of the O2 sensors. Usually, the exhaust would be very loud, if there was a leak..

I can take a look at it tomorrow quick. My exhaust is pretty loud, however the only place it could leak out is at the flange for the headers. I did replace the gasket and made sure everything was very tight. But if I have a leak after the cat and o2 sensor that won't effect it, correct??

It shouldn't have any effect. did you put a performance exhaust or just the stock type??

Porformance exhaust

Yeah, it should be ok. I put a performance exhaust system in my Jetta too and i havn't had any problems.

Was the TB dirty??