chugging/bucking

[chrisgreber]

so my 85/1 has this bucking crap going on whenever i let off the gas or get back on the gas out of a turn. its driving me INSANE. i don't know where to start. my guess would be injectors. but that is just a guess. other than that it runs perfect.
any suggestions would be greatly appreciated.

[white944cup]

Probably your auxillary air valve is clogged or sticking.......you might be able to clean it with carb cleaner or some other solvent that won't damage it. Iry searching for a cleaning procedure.

[vdubr928]

I think you are on to something with fuel. Injectors are dripping after shutoff and causing you to flood maybe. Id like to see video or somehing to confirm but the way you describe it that sounds legit. Has your milage dropped?

[rick13]

hey chris, when you figure it all out...please report back.

thanks,

rick

[chrisgreber]

im gonna search around a little more. my friends dad use to be a volkswagen/audi mechanic and he definitely thinks its a fuel related issue. i'll let you guys know when i figure it out.

[ERAU944]

on my 944, i have a hesitation when the car is cold (possibly what you might consider 'bucking')... i'm not entirely sure what the issue is, but the car has always done it, and it's not horrible. but i do know it shouldn't be happening.

my guess for my own issue is AFM - i will have to switch to a late DME/AFM to see if that makes a difference. if not, i will pop out the injectors, test them and clean them myself if they need it, and report back with the results. It may be a bit before i can put the other DME/AFM in the car, but i will keep my subscription to this thread and let's see if we can get to the bottom of this issue.

[chrisgreber]

well mine seems to be worse when its warm.

[vdubr928]

Does the car ever backfire? Is there a sound associated? There's so many different problems that could be described that way. Worse warm could indicate leaky injectors and worse preignition. Does it pop?

[chrisgreber]

FINALLY! i can't explain how happy this makes me. I spent about 3 hours in the california sun today, changing that damnn auxilary air valve today, and finally my car will idle again! and no more chugging or bucking. The part definitely was not cheap tho ($75 used), and its a pain in the aasss to get to. but so worth it.

[chrisgreber]

Originally Posted by vdubr928

Does the car ever backfire? Is there a sound associated? There's so many different problems that could be described that way. Worse warm could indicate leaky injectors and worse preignition. Does it pop?

and no, it didn't back fire or anything!

[Porsche924 mi]

Does it stop when you accelerate hard?
It may be a vacuum hose leak, i found a split on one of mine under the intake manifold.

[vdubr928]

Great. Easy fix. Glad your didn't have to bust the fuel rail.

[Porsche-O-Phile]

These cars are very finicky with respect to vacuum. When I bought my first 944 it started doing the same thing (chugging/bucking) after I got it home. The surging was enough to rattle my fillings loose - severe! It was just a small split in a couple of the "Y" vacuum connectors. That's it. Replaced for about 10 bucks and it ran like new. Still does. Just something to keep in mind for future reference.

[ERAU944]

The late DME/AFM doesn't seem to change my issue - and again my problem is only when the car is cold. I will try replacing the auxiliary air valve and see if that doesn't help.

Just for my own dumb arse, the AAV is under the intake, correct? While i'm in there, it'll be a thorough vacuum line replacement session.

[matty89]

Dme temperature sensor

The late DME/AFM doesn't seem to change my issue - and again my problem is only when the car is cold. I will try replacing the auxiliary air valve and see if that doesn't help.



Just for my own dumb arse, the AAV is under the intake, correct? While i'm in there, it'll be a thorough vacuum line replacement session.

[ERAU944]

Originally Posted by matty89

Dme temperature sensor

I just replaced the DME temp sensor. It fixed my on-throttle hesitation but has NOT affected my cold operation bucking.

When I begin driving first thing in the morning, the car falls flat on its face - almost like it's got a slug of water in the gas. car has full tank of fresh fuel and a brand new filter.

what gives?

I will try installing a new aux air valve next...

[rick13]

I have been patient with my hanging idle and bucking. I replaced my TPS and my idle is fixed. Also at highway speeds when I let off of the gas she seems to have settled down for the better. The chugging at highway speeds is virtually non-existant. I am going to replace injectors and put in MAF. I saw a kit at Lindsey racing. 80# injectors, MAF "M-tune" $1400...any thoughts?

[Chunkerz]

Get Josh's M-Tune from Rouge Tuning. It's 20 bucks cheaper and includes the 80# injectors.
http://www.roguetuning.com/951_maf_kit_m-tune%C2%A9