Crankcase pressure, deceleration "pulsing"

Hey all,

I've recently run in to an issue that is baffling both me & my local dealer.

After hard acceleration & in higher gears (5, 6) over 3k RPM, the car "bucks" on decel, almost as though the throttle is being lightly opened, then closed & so on. The problem is intermittent, but happens regularly when the car is hot.

Accompanying this problem is what seems to be excessive crankcase pressure, pushing oil past the seals in the valve cover/girdle. This was verified with UV dye. They may be unrelated.

Boost gauge reads normal vacuum at idle & it makes great peak boost (22+ lbs).

I pulled my GFB DV+ thinking that may have been the issue & it did have a worn seal & I didn't reinstall it, but with the stock rev. D valve, the problem persists.

I've replaced the PCV valve (latest rev.) & the PCV hoses.

I was running an ECS catch can, but bypasses it for the colder weather (it tends to fill & freeze). The problem seemed to appear after this, but that may be a coincidence.

It's a 2012 CBFA, K04, AWE boost hoses, Golf R intercooler, Fluidamper, Cobb Turbo-back, modified Volant intake, red top coils, Stratified ProTune via Cobb Access Port. Carbon cleaning was done with intake manifold replacement at 50k miles. It currently has 73,xxx miles.

The RSR clutch slips at torque peak, but that's being replaced in the spring.

Any insight would be appreciated.

Any codes? Could be throttle body or throttle body wiring issue. There is a bulletin for replacement of throttle body wiring (TSB 01-09-04).

I had same symptoms plus EPC light and code P0121. Dealer replaced throttle body and re-pinned the wires but symptoms are coming back once engine gets hot. Just replaced coilpacks to see if that makes a difference.

No codes (yet), I do have VAG-COM. I pulled the TB yesterday & cleaned it, though it was hardly even dirty. Ran a TB alignment afterwards. I'll ask my dealer about the TSB.

Edit: looks like that TSB is for '08-'09 vehicles. Mine's a 2012 (edited my OP)

I'm having compression & leakdown tests done next week just to rule out rings.

in 4 deets

out of curiosity, what type of oil are you running? My symptoms started after I used 0W oil for the 1st time (always used 5W since car was new). Probably a coincidence but who knows.

5w-30, dealer oil changes & OEM filters every 5k miles

Rings are good. Compression & leak down tests passed at my local dealer. Going to check the throttle body wiring next.

I was able to capture the phenomenon on my Access Port & I've sent it to Alex to have a look. I'll update once he replies. Looks like the ECU is both requesting & applying throttle in very small amounts randomly during decel.

I’m not having the bucking problem but there are sometimes some weird noises around 3k on decel. I am having the excessive cc pressure problems. My mechanic called me today of another car having the same problem as me. The only thing the three of us have in common is the Ecs cc kit. Don’t know if it’s weird coincidence or not but they’re suggesting I either go back to factory or get a cc that uses an Africa plate

redubbed said:

I was able to capture the phenomenon on my Access Port & I've sent it to Alex to have a look. I'll update once he replies. Looks like the ECU is both requesting & applying throttle in very small amounts randomly during decel.

Click to expand...

hmmm... odd that the tune would start acting this way all of a sudden. Keep us posted.

I'm going to clean my MAP, MAF, and AIT sensors this weekend. Not sure if things will improve. :iono:

That catch can is removed and it’s still occurring.

Alex at Stratified (can’t say enough nice things about these guys) sent me a revised tune. It seems to be helping, but I’m looking at replacing the throttle body if we can’t solve it.

I think you’re right about the tune, though. I’ve been on this rev for several thousand miles.

The car is also getting a clutch upgrade & intake manifold (IE) in the spring, so the tune will need to be “topped up” anyhow.

Car was checked for vacuum leaks, none found. Sent some more logs to Alex.

Throttle pedal has become a consideration.

redubbed said:

Throttle pedal has become a consideration.

Click to expand...

Interesting. Updates?

Nothing concrete. Replacing the throttle pedal this week at some point (when it arrives).

I’ll continue to update the thread.

Alex at Stratified has been a big help in trying to get it sorted, but even he thinks it’s hardware at this point.

I had that kind of bucking at low RPMs in first gear for years. It was the kind of bucking you get when you let the revs drop too low in a manual transmission equipped car just before you killed the engine. With mine the problem was it would happen at just over 1000 RPMs, and the car refused to cruise smoothly in traffic at low speeds. It was like my foot said “I want this throttle position” and the throttle body was hunting for it by sharply opening and closing the throttle. I had to ride the clutch to smooth it out so the engine bucking didn’t transfer to the rest of the car. I also saw an odd combination of warning lights every now and then.

For me the effective fix was to extend the wiring harness leading to the throttle body and replace the plug. Smooth as silk at low RPMs now. I can’t believe I put up with that for years.