idling weird

[alxjhn]

have a 1998 volkswagon jetta 2.0, 5 speed. i took the throttle body off and cleaned it because the previous owner never changed the air filter so there was a lot of oil in the air line. i took everything a part and cleaned it. i installed a new throttle body gasket and cleaned everything. now the idle is really wierd it idles up and down. it goes up to 1200 and then it comes down to 800. the rpm just goes up and down, up and down. it happens sometimes not all the time. i searched couldn't find anything. ANY IDEAS.

PCV valve??????
or that little sensor that connects from pcv valve to air tube??????

[MKIIVR6]

Check you wire harness connection point for the MAF (mass air flow sensor) or other harness connections in/around where you were working. Let the car idle, gently push/pull the harness connections. If the idle suddenly changes or smooths out thats where the problem may be. On both my digifant II and my currentl motronic setup both maf connection points have seem to have had issues at one point or another.

Another possible issue could be vaccuum or an air leak behind the MAF sensor. An easy way to diagnose this is to lightly spray carb cleaner in the areas where you were working. If the idle changes you'll be able to find the issue pretty quickly.

[Mr_Diesel]

Another thing that could cause a wierd idle is the ISV. I think the OBD 2 2.0L engines don't have these, but you never know. Check and make sure that all the tubes and connections on the air intake hose are tight. Also, check for tears in the air intake tube (it happens frequently with this design). Also, make sure there is no residue on the MAF sensor board.

FYI, you will always get oil on your throttle bod and in the air intake hose... It is just the nature of a high mileage engine with heavy blowby. My 2.0L engine had a fair amount of blowby and it always can collect in the air intake hose.

The main thing you need to make sure is that you alway replace the air filter. The oil in the hose is fine. What is NOT fine is when dust and dirt gets past the filter element and mixes with this oil. You'll get nasty greasy buildup that will cause issues with the throttle body. Bigger issues with the EGR too (if equipped).

It would probably be good practice to simply spray some throttle body cleaner down the inside of the air intake hose and on the inside of the throttle body once every year... Probably on your Spring / Post Summer tune up. No need to remove the throttle body.

On another note, welcome to dubnet, man... You have one of Volkswagen's most reliable cars. The 2.0L aba engine is a tried and true design... Very good bottom end torque, and excellent economy at the same time. My 94 Jetta had this engine. I had a lot of experience with many things on this motor. If you have any questions don't hesitate to ask.

[alxjhn]

good lucking out with the info man. i replaced the air filter and everything. people say i have to adapt the throttle. how? i also replaced the battery yesterday.

[Mr_Diesel]

Adapt the throttle??? Dunno what that means. Does your car have an ISV? It's a motor looking thinggy about the size of a....... grenade? (first thing I could think of) it's got 2 hoses going in and out of it. Should be mounted on the intake manifold.

[alxjhn]

i have on of those things

[Mr_Diesel]

I just noticed this was never replied to... Did you ever resolve this?:D

[zukgod1]

If you havent fixed this yet do this.

Turn your key to thr "Run" position but do not start it.
Let it sit for approx 2 min, turn key off then restart.

I'm betting it will be all better.
The ECM needs to Relearn the T Body once it's been unpluged.


Dan