# Studdering badly at low rpms



## ShadetreeSHOguy (Jun 25, 2006)

Hey guys(and gals).

I'm relatively new to this CIS stuff and ive narrowed it down to an issue with the fuel.

I've got an 84 MK2 GTI that I'm having troubles with.

What's happening is at below 2500ish rpm at part throttle the car misses and studders VERY bad. If i go WOT or above 3k it goes away. 

I'm guessing it might be a frequency valve or the injector orings leaking, but im not sure.

Any help would be greatly appreciated


----------



## cuppie (May 4, 2005)

First off, everyone here (myself included) is going to recommend that you buy the Bentley for your car. They're a wealth of information, including how to troubleshoot the fuel system.

Second: whatcha working on? Year, model, engine? 

When does the issue occur? Cold? Warm? Both? 

Check it for intake leaks yet? Grab a can of carb cleaner, and start the engine (not when it's screaming hot!) Start spraying at points on the intake - if you hit a leak, the idle will change.

Injector o-rings are a common leak point, are (theoretically) easy to change, and are cheap.
Vacuum hoses deteriorate. Just change them.
Intake boots are known to split, and will play absolute hell with driveabilty. Remove them, and carefully inspect inside and out - flashlight helps. Find cracks? Replace boot.


If the issue occurs _only_ when the engine is (about) at operating temp, a dead O2 sensor is a good possibility. Umplug it (the single-pin plug on the firewall), and take her out for a drive. Run better? Replace O2.


----------



## ShadetreeSHOguy (Jun 25, 2006)

Heyy, THanks for the advice.

THis is an 84 mk2 GTI 

8v with cis of course, lol.

I've done the carb cleaner test and the rpms do not change.

and it's more noticeable when it's cold. but it does it at all temps

I'll try the o2 sensor tommorow


----------



## erty67 (Feb 23, 2010)

why your checking out the injectors rings, lift the plate and see how good they're spraying. You could also have a bad injector.


----------



## cwismk4 (Oct 11, 2010)

did you ever figure it out, i have the same problem and cant figure it out:banghead:


----------



## vdubz06 (Nov 10, 2006)

*84 Rocco 8v CIS*

All this sounds much like my issue with the Scirocco.. below ~2500 it studders, when I open throttle I get a loud sound from my air box as if I had a million holes drilled in it, then it passes that point and revvs like a champ. When I put it into gear to drive it bucks and hesitates like the engine had a choke on it. I unplugged the O2 and the engine ran worse.. If you figured anything out I could really use some direction. Thanks- Keith


----------



## cuppie (May 4, 2005)

How does the engine start? How does it idle?
Has it been 'tampered' with?
Is there any temp range where it does run correctly? Or, engine temp doesn't matter?
Any backstory on this that we should know about?

Generally, low-throttle / low-speed issues are intake leaks; high-throttle / high-speed issues are fuelling issues. Generally.

Standard advice is as follows:
- clean up the grounds on the back of the head (engine management), and at the B- clamp (ignition.) Make sure that the coil ground strap is present, and in good condition.
(While you're at it, it's not a bad idea to just go on a cleaning kick with all of the battery cable connections, clear to the alternator. It probably needs it.)
- inspect engine very thoroughly for intake leaks. Grab a can of carb cleaner, and start spraying places. Injector seals are common failure points. 
Just replace all of the small-diameter vacuum hoses. Hose is cheap.
Remove intake boot, and very thoroughly inspect it, inside and out, for cracks. Replace if needed.
*Reminder on intake leaks:* a missing or broken oil dipstick (or dipstick funnel) is an intake leak. A cracked/broken/missing engine-vent line (or elbow, or even the grommet in the valve cover) is an intake leak. A leaking oil cap is an intake leak (even a leaking valve-cover gasket can piss it off.) Repair or replace parts as needed.


----------



## anthonymar1 (May 12, 2009)

i bet its your airflow plate in the airbox. had the same exact problem


vdubz06 said:


> All this sounds much like my issue with the Scirocco.. below ~2500 it studders, when I open throttle I get a loud sound from my air box as if I had a million holes drilled in it, then it passes that point and revvs like a champ. When I put it into gear to drive it bucks and hesitates like the engine had a choke on it. I unplugged the O2 and the engine ran worse.. If you figured anything out I could really use some direction. Thanks- Keith


----------



## ps2375 (Aug 13, 2003)

Sounds to me like one or two bad injectors. Before I changed my car to MS, I had a similar problem (based upon your description), and it turned out to be one bad injector. It was fairly easy to determine the cylinder by pulling the spark plugs, after running it with the miss. That plug was fouled, it seems as that injector was spraying too much and when the rpm's came up, the A/F mixture for that cylinder got better and the car would take off. But, that is just one of many things it could be.


----------



## Glegor (Mar 31, 2008)

ShadetreeSHOguy said:


> Heyy, THanks for the advice.
> 
> THis is an 84 mk2 GTI
> 
> ...


 
if its a mk2, its NOT an 84.. 

if its an 84, its NOT a mk2.. 

so, witch is it? mk1, and mk2 GTIs came with very different fuel injection systems..


----------



## WaterWheels (Aug 14, 2005)

Glegor said:


> if its a mk2, its NOT an 84..
> 
> if its an 84, its NOT a mk2..


I know, I know, but maybe, just maybe he is not located in The United States of America. In Europe an 84 can very well be an mk2. Might be wise to post something more like, "Where are you located because here where *I* live 84's are mot mk1's but rather mk2's?" Just a thought.


----------



## vdubz06 (Nov 10, 2006)

*FIXED!!*

All of my symptoms described were fixed by replacement of the ignition control module.. $62 part and very easy to install. Thanks guys! and good luck to the rest of you!!


----------



## jetta1986 (Dec 27, 2004)

I'm having the same problem


----------



## Glegor (Mar 31, 2008)

WaterWheels said:


> I know, I know, but maybe, just maybe he is not located in The United States of America. In Europe an 84 can very well be an mk2. Might be wise to post something more like, "Where are you located because here where *I* live 84's are mot mk1's but rather mk2's?" Just a thought.


ShadetreeSHOguy... that doesnt sound too european to me.

im gonna go out on a limb and just say hes a newbie, and really doesnt have much of an idea what his car is, besides its an 84 VW.


----------

