My 1994 VW Golf (2.0L) has 200,000 miles and is still going strong with the exception of an idle fluctuation problem. This car typically idles around 800 to 900 RPM, but it now intermittently will idle as high as 2000 RPM, and will often fluctuate randomly between these rates.
I was pretty sure this problem was caused by a dirty/ stuck Idle Air Control Valve, especially since I could tap on this valve (with a metal tool) when the engine was idling high, and it would drop right back down to 800 RPM.
I have replaced the IAC valve with a brand-new Bosch OEM part, and the problem still exists. I can even ‘tap’ on this new valve at high idle, and the RPMs will drop down to the correct level, just like the old part did.
In addition to replacing the IAC valve, I have also cleaned the big throttle valve and the intake manifold around the throttle valve.
I am interested in finding out what other problems can result in a fluctuating idle condition, and if anyone can help me understand why the new IAC valve would behave the same as the old valve when I tap on it. Did I just get a bad part, or is the root cause of the problem more likely something else?
Any help would be greatly appreciated.