accelguy

Having installed a new MAF 996.606.124.00 + reset ECU, the problem didn't go away.

Car has the following
Throttle body cleaned & New stock spark plugs, Injectors cleaned with Redline Si-1 3000km ago
Billet DV
UMW remap
200 cell exhaust
Stock hollow wheels n tires

My car has developed 3 symptoms recently

1. engine rev hunting @ idle (almost stalled feeling) &
2. engine rev rising and dropping (bouncy rev) under 2000rpm
3. ABS/PSM comes on @ off throttle + bouncy pot holes.

To better describe symptom #2, the car drives perfectly at WOT or with a slightly heavier right foot. There is no boost leak or power loss. It sits at 1.1 bar at peak boost and no vibration or engine rev rising or dropping during WOT. All bouncy engine happen rev below 2000rpm at cursing speed.

Does symptom #3 suggests new a ABS sensor kit?

What should I do to cure symptom #2 the bouncy rev?

accelguy

Symptom #1 Just been out driving and found the car to idle at a around 800 rpm and whenever it drops to around 750 rpm, it revs up to nearly 950-1000 rpm. The whole process simply repeats itself most of the time at traffic light.

Symptom #2 happens mostly on highway in 5th gear under 2000 rpm. It does so in 2nd, 3rd and 4th too. The rev counter just goes up and down between 1700-1900 rpm.

"02996ttx50

sounds like a boost leak to me. you can still hit full boost with a minor leak in many cases. i would check the turbo inlet hoses for one being partially pooped off. hunting idle even with new maf are the clues

edit: though your second sentence in your second post would seem to contradict my guess. ( i wouldn't drive under 2k rpm )

( MY 2000?! )

drh

Check the boost hoses where they connect to both the plenum and the intercoolers

accelguy

Hi 02996ttx50,

Thanks for your reply.

Where is the turbo inlet hoses located? Are those the 2 great big black plastic tubes that can be seen connected to the intercooler above in the engine compartment?

Thanks again

drh

http://www.renntrack.com/forums/show...boost-hose-diy

"02996ttx50

yep follow em down to the i'c's as drh has also noted. bumper off is best, as i'm not sure they can be reached otherwise. exact symptoms as you described and that was the cause. minor yet noticeable in the way you described. gl w it.

accelguy

Hi 02996ttx50 and drh,

Thank you for your replies.

Am I right to think boost leak must affect boost values at WOT? i.e. at WOT, not being able to hit max boost or boost surge or over boost or hesitation.

Where can I buy those Samco boost hoses? They do look good.

Thanks again

"02996ttx50

one would think so.

enzowho

From my experience, a boost leak does not impact the reading on the boost gauge on your instrument cluster. My stock x50 hit 0.9 with a pretty severe leak. Had lots of idle hunting issues desire new maf, plugs, coils, ect. Immediately went away when the leak was fixed.

LLTurbo

Dumb question but what is the maximum boost on a stock non-x50 and in what rpm range and or gear do you achieve it? I like watching the road when I'm flooring it, and I've typically just looked in 2nd and 3rd gear haven't seen above 0.6 bar.

"02996ttx50

you're pretty close to max boost on the gauge but you should see .7 on a k16 and .9 in an x50. it's the spikes of .1 extra on cold wet days that bring that extra fleeting moment of joy lol.

don't be dismayed if you only get .6 though, proper conditions should see the .7. esp above 2750 at wot in 3rd or 4th should do it

Kevinmacd

The UMW should probably give you max boost around 1 bar. Drop any codes?

Macster

Max. boost varies based on the torque demanded by the driver and road/climatic conditions.

I live in the same general area as you and I can see 0.7 bar boost when hard (and I mean hard) accelerating in 4th or 5th gear starting at 2K RPM climbing the Dublin grade on I-580 west bound just past the I-680 freeway. Max. boost shows up at over 3K RPM and drops off as RPMs climb to 4K and beyond. Things happen pretty quickly when on boost so I can't offer much detail as I'm pretty busy steering the car and watching what little traffic there is when I do this.

At higher elevations like climbing the grade -- in either direction -- heading up to Tehachapi on 58 highway or at various "passes" on I-40 west of Barstow on into AZ and NM the boost display will show 0.7 bar even 0.8 bar and not just a brief time either but the reading will remain for a few seconds.

At various places I've seen 0.8 bar even 0.9 bar at elevations above 8K feet -- on I-80 in Wyoming.

accelguy

Hi Kevinmacd, Macster and everybody,

My UMW is giving me max 1.1 bar at WOT. Even with the suspected vacuum leak, the boost shown on the dash is stable and power delivery is smooth. I do not feel any power loss and the car is still as fast as before according to my accelerometer.

Since the new MAF, I have done 100km. The car threw ABS/PSM CEL on the dash occasionally and the P0102 Factory Fault Code 115 - Mass air flow sensor, below limit was read. Furthermore, No other fault code with engine, tiptronic or abs/psm was read by the durametric. Have you got any idea why it had caused the P0102 code?

In the attached photos, the 2 hoses that I circled in red are in fact linked together with part of it linking to the great black metal y-pipe that connects to the throttle body. Having sprayed some crab cleaner to these 2 hoses, I found that the rev counter definitely dropped and therefore I suspect there to be leaks. Fortunately, I was told that hose is the breather hose from the oil tanks mounted on the turbochargers. I also sprayed some crab cleaner onto the F hose that connects the 2 DVs, the Intercooler hoses and the hoses on the N75 boost solenoid but found no rev dropping. Do you think this breather hose is the culprit? And should I go out and datalog any particular value to narrow down the issue?

Thank you very much for your help