Car Running Rough, Need Help.

[blackmirage]

I tried the newbie forum but I Guess maybe they may not know the answers to my question, so I'm posting it here. Sorry for the double post.

Hey guys, I've just purchased not too long ago a 1990 AWD TSI, and it runs rough. When I first got it we drove it home and it wouldnt go above 2800-3000rpm constantly building boost apparently and the fumes it was emitting were herendous. Well once we got it home we found that at the downpipe and the cat there were no gaskets and it was leaking. So right now the car is running with only a downpipe. We checked the plugs and Cylinder 4 the one farthest from the driver side, was full of oil. 3,2,1 were not filled with oil but JET BLACK, so we changed the plugs and all the seals and gaskets on the Valve Cover. Oh and by the way the previous owner had the firing order ALL wrong. So we fixed that. Then we noticed that the Exhaust manifold was smoking/leaking. and this wasnt from the liquid wrench we sprayed on anything because it should have burned off by now, so we took the manifold bolts off and brought the manifold back as far as it would go so we didnt have to take EVERYTHING off and put the new gasket in. No smoke for the most part, there is a very minute amt of smoking now, but we are thnking maybe its cracked on the underside where we cant see. We changed the air filter because well it was NASTY.... Now you know where we stand, my most prevelant problem is that the car wont rev past the mentioned 2800-3000 rpm UNLESS the Air Flow sensor in the intake is unplugged. with it plugged in it throws a CEL and it wont run very well. Do you think that this is caused by a bad Air Flow Sensor? I'm trying to get this running so I'll be coming back to this thread with all my ?'s. But I am reading alot and looking at the VFAQ, so yes I am doing my searching. Sorry for the long post, I appreciate any and all help.. THANKS!

 

[bmwisthekey]

so the CEL light is on only when the airflow sensor is unplugged, ok, while your in the vfaq try looking into doing a boost leak test do the test, inspect visually, listen, spray soapy water. also in the vfaq it shows u how to check the CEL lights just try getting the codes with the airflow sensor plugged in if there is any, or if possible if you know someone u could try swapping sensors with 90-94 talon/laser/eclipse turbo.

 

[blackmirage]

Yeah and it wont let me continue past 3000rpm unless it is unplugged. Has that every happened to anyone?

 

[hidingfrogleap]

So by saying it won't let you rev past 3k, you mean you go in on the throttle all the way and it just holds at 3k? or is it throwing you a CEL when you go past 3k?

 

[yekrahs]

well if you have the maf sensor unplugged it defenelty won't rev past 3k becuase your ecu has no idea of the amount of air thats getting sucked in....If you did a boost leak test, and got no bad results, you can either try new plugs or wires. but your plugs being black indicates running rich, check and make sure all of your exhuast manifold bolts are really tight becuase that wll cause an extreme boost leak? If I think of anything else I"ll post it up

 

[blackmirage]

OK, Hiding to answer your question. When at Idle it wont let me rev past 3k, when driving it wont either. it just looses all power bogs down what have you... CEL is SOMETIMES on SOMETIMES not. Its weird.
Yekrahs, I agree tottally with you, but the thing that boggles my mind is this happens WITH the maf plugged in. with it unplugged I can rev all the way to 5-6k and drives decent enough to get to AutoZone or something down the street. I'm just lost at this point, and dont really wanna just throw all kinds of new parts at it that arent going to solve the problem. I really appreciate you guys brainstorming wit me though, thanks.

 

[1g_TaLoN]

i think that it sounds like maf sensor to me . dont know why it is running without it pluged in though.
PS. a leaking exhaust manifold no matter how bad will never ever cause a boost leak.

 

[blackmirage]

Sounds like the maf to me, but it would make sense if it was turned around. you know what I mean. If It was unplugged and only ran to 2-3k I would understand... but this.. I just dont get... Yeah the exhaust leak may not cause boost leak... but would it not cause an issue with the O2 sensor and what the ecu thinks?

 

[hidingfrogleap]

Yeah, it sounds like a problem with your MAFS. Kind of sounds as if not enough air is getting through or it's sending too much fuel for the amount of air it's letting in. Since with the black plugs indicating you're running rich, your air/fuel ratio must be off which could well have been caused by an incorrect amount or reading of the amount of air. That would explain why if you unplug the mafs it runs fine since air is still getting pulled though the piping regardless. I'd say start at your mafs and work backwards from there.