Hi everyone,

I am still struggling with the idle motor speed.
I could graphically describe it as a typical sinusoidal wave. When I start up the engine and its speed goes down below 800 rpms (the engine warmed up) and you might think its idle speed is going to normalize - it starts to act up
The motor idle speed drops below 500 rpms to the point that the entire car starts to shake and you think it is going to stall at his moment - it does not. The rpms almost double and increase up to about 900. Then, they decrease again down to approx. 450 rpms.
The whole cycle lasts about 7-8 seconds.
It happens only while in idle (e.g. waiting on the red light).

The scanner finds two codes as follows:

P0234 - due to a possible leak in the intake air system, an implausible signal was received from oxygen sensor1.


P0153 - O2 sensor circuit slow response Bank 2 Sensor 1.


Intake manifold changeover - SHORT

What I have done so far to fix the problem:
1. I replaced eight old (still the original) spark plugs with a brand new set of NGK Laser Platinum PLKR7A. (Konigstiger, thank you again for the instructions with the torque specs).
It did not help to fix the problem.
2. I replaced the Bank 2 Sensor 1 - O2 sensor after a real and long fight to remove it.

It did not help.

4. I replaced the old air filters with a set of new ones.

It did not help.

Has anyone had that problem before with a positive outcome, solution and is willing to share it with us, please?
Is my next step to "dig deeper", remove the intake manifold and look for some abnormalities there?
Konigstiger, if you are reading this please share the instructions with me on how to remove the intake manifold. I am ready to roll up my sleeves again, and I am determined to resolve the mystery and fix the problem once and for all.

Any help will be greatly appreciated.

Thank you in advance.
Pitek

 

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