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Diagnostic help needed


Paul

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With the nice weather have been able to take the car on a few runs. Met up with Fritz in TV who graciously helped with replacement of fuel pump. On the way to TV noticed the car would have slight hesitation while cruising in the first three gears. No issues while excelerating, pulls strong, only when trying to maintain a constant speed does it feel a bit "jerky" ever so slightly. Initially wrote this off as confirmation that a new fuel pump was needed. However, after install and with subsequent test romps, problem still exists.

 

What could this be? Have new plugs and wires installed, new fuel pump. Could this be a clutch issue? Transmission? Engine? Fuel filter?

 

Have done some research on the pelican forum yet nothing conclusive. Thinking of trying a fuel system cleaner additive (BG 44K).

 

Again car pulls strong in all gears to red line but problem only manifests itself while cruising in a gear.

 

Any suggestions would be greatly appreciated.

 

Paul

‘12 Targa 4S - Amythist metallic

'81 SC Targa - sold but not forgotten

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Thanks Fritz,

 

Did just that and the resounding consensus is that it has to do with the air fuel mixture. On that note I do recall when the car was in for service last summer that the mechanic said he adjusted things to run a little richer as well as adjusting the idle speed (increase). On inspection before putting the car on the road it was noticed that the O2 sensor was disconnected in the engine compartment and the wire wrapped around one of the heater hoses.

 

My question then would be, if the shop disconnected the O2 sensor and then made adjustments to compensate, would this then create a problem as experienced when the O2 sensor is connected? I do not recall having this problem last fall (when the sensor was not connected).

 

I will disconnect the sensor and take the car for a spin and see what happens. Is it a problem to continuously drive with the O2 disconnected? Or is this just going to create even bigger issues?

 

Paul.

‘12 Targa 4S - Amythist metallic

'81 SC Targa - sold but not forgotten

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Paul, I think you should connect the O2 sensor again and than readj. the fuel mixture. I have a Fuel/air ratio meter and we could play around.

You have to find some body which knows a bit more about your fuel injection system. I am more knowledgeable on the older engines.

 

 

Fritz

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Ok, just took the car for a test drive with the O2 sensor unplugged. Ran like a champ. Pulled strong, no jerky feel while cruising at a constant speed and rpm.

 

So, the million dollar question is why would the shop do this? Idle rpm is slightly higher, 1050 rather than 950 at start up. Dips to 1000 after a few minutes.

 

Any long term consequences of running the car with the O2 sensor disconnected?

 

Paul

‘12 Targa 4S - Amythist metallic

'81 SC Targa - sold but not forgotten

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Thanks Fritz,

 

Will phone the shop to get an explanation as to what their line of thinking is.

‘12 Targa 4S - Amythist metallic

'81 SC Targa - sold but not forgotten

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Guest gofaster

Source: http://www.renntech.org/forums/index.php?/tutorials/article/59-diy-throttle-body-cleaning/

 

"One of the problems with many 996/986/997/987 owners complaining about is a lumpy or erratic idle and sometimes sluggish acceleration.

 

The issue is that over time a sludgy gunk will build up in the throttle body where the throttle butterfly opens and closes. This gunk will eventually change the airflow characteristics of the gap between the butterfly and the throttlebody which will cause the erratic idle. In addition, this gunk can cause the butterfly the stick as it opens which will effect acceleration.

 

The car's DME will compensate for this buildup over time, but if it gets too thick, then the "Throttle Adaption" will reach its limit, and will throw a code. Many times people think that it is the MAF that is bad, when it is just a dirty throttle body.

 

Notice that the butterfly valve is slightly cracked open. This is for the idle airflow, and that crack can get clogged because of the gunk buildup.

 

The solution is to remove the air cleaner box for access to the throttle body, and simply clean the throttle body with spray carburetor cleaner.

 

Open the butterfly valve with your hand, and wipe out all of the gunk on the backside of the valve, and the inside of the throttle body. You will see a dark brown ring inside the throttle body. This is the buildup you want to remove.

 

Take a rag, wet it with carburetor cleaner, and wipe out the gunk. Be sure to get the edge and the back side of the butterfly valve as well. You will know when you are done because the surfaces that you are cleaning are polished, and easy to see if there is stuff left on them.

 

Don't worry if you spray too much in the engine, when you fire the engine up, all of that stuff will burn off in the combustion chamber.

 

Where does the gunk come from? It is residue from the crankcase vent opening that is right there behind the butterfly. The reason it is there is because there is high vacuum there that will suck the crankcase oil vapors back into the combustion process of the car. Over time oil solids will accumulate there and will form a sticky lip around the opening.

 

This cleaning should be part of your 30,000 mile maintenance as a minimum. However if you have never had your throttle body cleaned, try doing this weekend. You will be amazed at how much better your car runs."

 

Source: http://www.renntech.org/forums/index.php?/tutorials/article/59-diy-throttle-body-cleaning/

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Keith Adams
Any long term consequences of running the car with the O2 sensor disconnected?

 

Paul

Paul this was a common occurrence in VW Vanagons (the only basis of reference I have!). The only risk to running with the O2 sensor disconnected is that the car will run rich sometimes and then foul the catalytic convertor. If you are running without a cat, it should be fine until you can replace it.

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