daysls

Hello,
This is the problem:
When I start my car it will idle normally for about 5 minutes then the rpms will slowly rise until 1800ish and the drop to 1000. but the strange thing is it is very inconsistent, sometimes it will just hover around 1000 and not change. Now this may or may not have anything to do with it but i cleaned the throttle body because it was idling low. it fixed that problem now its idling high. I did notice that when i pulled off my air hose to the throttle body it had alot of oil (coming from the air cooler on the bottom of the car) i assume this is because the last guy that changed my oil overfilled it by a half quart.
This is what I have done:
-Throttle body adaption (VAGCOM)
-replaced throttle body gasket (twice to be sure)
-cleaned MAF
-checked all vacuum lines with starting fluid
-checked evap valve thing that clicks ontop of the airbox (forgot the name)
-replaced thermostat
-replaced coolant temp sensor
This is where I am at:
all of the things listed above have greatly improved my mileage, before i had heat but no temp gauge so thats why I replaced that. now my temp gauge reads. I have no codes. my car has 120k and was redone at 100k. I have no performance mods. I noticed that my voltage is about 14v but when i turn the A/C on and headlights It drops to about 12v. I also noticed that when I take the gas cap off after a long drive there is a large pressure release.
My question is:
What do I do now?

daysls

Also I have cleaned the IAT sensor.

4Driver4

Pull some codes?

daysls

There are none did a full scan with the vagcom and nothing.

Prospeeder

Check all the PCV plumbing under the intake. Theres a large black plastic pipe, a rubber 'T' and a PCV valve stuck in with a hose coming off. If you see oil and grease caked on all these parts replace all 3 peices. PCV valve is plastic and will break and cause a wide open vacuum leak and high idle also.

I have also seen throttle bodies fail and idle hunt like crazy, but its usually not temperature sensitive but resistances change with temp so why couldnt it. They sometimes never set codes either and adapt fine.

daysls

Thanks Prospeeder
I will check these later, do you have an image of this? maybe it would help.

daysls

So I replaced the PCV check valve. noting changed I did how ever notice a new problem. When I pull off the oil cap while the car is running, there is a large amount of positive pressure. What can cause this? also I read that it would be a good idea to check the N75 valve. When I unplug the valve(the wire plug) and drive it, it makes no difference in the car. What should I do next?

daysls

So here is an update. after checking for vacuum leaks, I found that I had a bad diverter valve. I replaced the valve with an upgraded version and she runs like new.

David.Norton

Either the PCV system is plugged, or you have a lot of blow by. Hope for the first, the second is an engine rebuild.

sonny17

Did you ever figure out the positive pressure issue? I have the same issues.