First of all, if this problem has been answered in the past my apologies. I've been searching but I haven't found this specific situation answered. There's tons of information on similar issues but mine seems to be slightly unique.

I recently bought a 2001 996TT, beautiful car. Though the dealer turned out to be lacking...

On the drive home I discovered the Alternator was shot. Got that replaced and the car was running solid... Then I started to notice small surging below 2000rpm.

Over the next few weeks the surging got worse, and during hard pulls I started feeling power drops. If I eased off the gas it'd start to pull again.

I've had a P0491 code twice but that seems to only affect emissions and not drive ability.

Now the car is parked for the year but just to add a little more irritation it's now hunting on idle, surging throughout the power band, and dropping boost.

So to summarize my issues:

- P0491 code
- Hunting at idle
- Minor surging at low RPM
- Boost drops under hard acceleration

Any thoughts? Bad vacuum line? Bad MAF? Bad diverter valves?

My car came with:

- EMS Intake
- Fabspeed Exhaust
- Fabspeed High Flow Cats
- A tune that allows 1.0 Bar boost
(Stock Diverter Valves)

Any feedback / help would be greatly appreciated

 

possible failing maf along with ( possibly ) a minor leak which might also answer the "hunting". doesn''t take much of a leak to lose boost.

 

I was thinking the same two things. Hopefully I can dig down and see what where the problem is so that I don't have to replace the whole kit.

 

although i'm confident those two issues are the cause in some combination? boost leaks are beyond the scope of my ( ahem ) *expertise*

but i have had hunting and bad mafs. part of the joy.. right? if you're "capable", i would do the old boost leak test ( check first at the y-pipe ) and replace ( NOT clean sheesh..lol ) the maf. if not? i hope you have a knowledgeable and honest shop. t-shooting and chasing these kinds of things down can be very expensive if amatuers are involved. but this you know. but those two items are where i would begin, for sure. GL! w it!

 

Thanks for the suggested areas to target! Hopefully I'll hammer out the failures before filing for bankruptcy

 

The MAF check is really easy. Unplug it and then go for a drive. Be aware that your traction control and ABS will be shut off when the MAF is unplugged. It make for a bit of a scary ride. If the drivability issues disappear order a new MAF. I got mine from amazon 3 weeks ago for 152 and no tax but I am in the US so your cost may differ. Amazon was definitely the least expensive for a bosch part.

 

I think I'll try out the MAF test either tonight or this weekend. It'd certainly be the easiest fix, but unfortunately my tune requires a Hitachi MAF which I believe is a little over $600. I'd still rather operate with the pay to play easy fix over tearing apart my Secondary Air Injection system.

Worst case, it'll be the ol' corroborator cleaner vacuum leak test / soap and water boost leak test.

At least with the snow coming and the car more or less put away I'm not itching yet.

 

If your tune has the hitachi MAF, may not be the MAF. However, the hitachi MAF is about the same price as the Bosch unit. I believe if you search around here it is the same as the Audi S4 from early 2000's unit. If you can get a hold of durametric, you might be able to see what is going on. Look at secondary air pump and vacuum leaks as another possibility. Boost leak would be pretty obvious I would think

 

Yea I'm looking at getting the Durametric cable soon regardless of if I get this fixed. Anyone know what the part number is on the Hitachi MAF off hand? I'd have to pull it to see the part number as it's situated in a bad position.