911 3.0 litre engine hunting

[tjasj]

I recently encountered a problem with my 1978 3.0ltr that continually had the engine hunting (continually idling at 900rpm then moved 3000rpm droped back down and moved up again every 2 seconds - this would go on indefinately). Took it to my local mechanic who could not diagnose fault after 2 days of continually working with it. Handed it back to me with the idle set fast (2000rpm to overcome the hunting effect).

After searching the web and many informative threads about engine hunting and possible causes, I eventually convinced myself that the problem was electrically related. My problem, as I self diagnosed it and subsequently fixed it, was related to zero voltage going to the vacumm controlled warm up regulator. Tracing this back, lead me to a dry solder joint in the main engine harness connector, which when I resoldered it and started the engine it was like a new motor.

I posted this in the hope that it may offer others another avenue of fault finding with engine hunting issues as I had read many, many different possible causes from fuel to air flow to electrical.

I lived with this problem for almost 3 months, had my car out of action with mechanics for a total of 2 weeks, the problem took less than 5 mins to fix.

Edited September 6, 2007 by tjasj