Quote:
Originally Posted by Rundtinden
Deleted the codes, unplugged the MAF and started the car. No difference. Car runs, but with the same symptoms as before. Will clean the throttlebody and valve tomorrow. What other possibilities are there? Random misfire reported on all sylinders. No vaacum leak found. Can it be the AOS?
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On a stock engine the symptoms your describing:
Idle hunting from low to high idle.
Rough running at low RPM but improves with higher RPM
Those are both classic symptoms of intake air issues.
The three main causes are:
Vacuum leak
Faulty MAF sensor
And in your case because you have a IACV =Intake Air Control Valve on the throttle body.
The IACV.
Then there are other less likely causes like bad valve timing which again is related to the intake air.
So everything I read in your posts says to me there is some issue related to intake air.
I could be wrong but it seems the most likely based on your info.
You also checked the most likely electrical issues and found them good.
Your misfires:
They can be caused by a vacuum leak.
But they can also be caused by electrical issues.
such as fouled plugs
failing coils
issues with the wiring
bad valve timing
bad ignition timing.
A major issue with your situation is that the intake air system has been modified.
The potential problem being:
The DME/ECU is in a stock configuration and is not able to fully adapt to the larger throttle body and larger or different plenum. And different MAF sensor Or Correct MAF sensor for the stock configuration in a not stock plenum.
So it is possible that the Info from the MAF is just not working with the intake mods.
Because you have mods to the intake air system it makes it very hard to isolate problems like yours because the mods are not configured for the DME/ECU
Vacuum leaks:
A smoke test.
Vacuum test with a test gauge.
using starter fluid
None of them are 100% positive tests.
Here is why: You have the SAI the EVAP system and the AOS. brake booster.
They all use vacuum from the intake. the SAI and EVAP have one way valves that are electrically triggered. The valves can be fine but have a vacuum leak issue on the down stream side. So no vacuum leak tell the valve is open.
A smoke test will not show this because the one way valve is close with engine off.
A Test with a vacuum gauge may not detect the vacuum leak because the one way valve may not be open while testing at idle.
They only use vacuum part time.
Yes it could be related to the AOS but you need to do a PROPER test of the AOS.
That takes a special vacuum gauge connected to a modified oil filler cap.
It tests vacuum in the crankcase.
Some people do this by feeling how easy or hard it is to remove the oil fill cap while the engine is running. But that is not a proper test. It is just guessing.
If cleaning your throttle body and cleaning the IACV do nothing to fix your issue. You may want to consider putting the stock air intake system back on and see if that fixes the issue.
Of course if you no longer have the parts that is not an option.
Hope this helps in some way.
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