Since I got my 84 245, it has idled erratically, surging up & dying down about once per second. It's subtle, and overall the car runs fine, but it's worrying. It's worse when the engine is hot.
I recently had the fuel pre-pump replaced. Should I suspect the main pump next, or look to the plugs/electrical system?
If you haven't already, the easiest thing to do is clean the throat of the throttle body with carb cleaner around where the edge of the round butterfly valve closes. Oil/grease buildup prevents complete closure, allowing too much oxygen and sputtering condition that you describe. Also clean the vacuum hose nipples on the outside of the throttle body, using carb cleaner and a thin wire or pipe cleaner.
Though a dirty throttle body is not the only cause of erratic idle, it is very common, and very easy/cheap to correct.
Let us know if the problem goes deeper...
You've almost certainly got a big vacuum leak somewhere under the hood. Check all the vac hoses, particularly the ones to the carbon cannister and the brake booster hose, look for any nipples on the intake manifold that a hose may have fallen off of.
Look at the idle air control valve (under the intake manifold). You may have a pin hole in the air intake hose between the mass air flow meter and the throttle body.
Yep, this CIS valve is one of the prime offenders when you have this type of idle issue.
Thanks very much all, for the advice.
One question: If it IS a pinhole in that hose, how do I fix it? New hose? Is it just any old hose of the proper size, or is it some special swedish hose? :-)
New hose is ideal, it's a custom part you can get from the dealer. You should be able to fix a pinhole with some silicone caulk (make sure you use the sensor-safe stuff) or some shoe goo in a pinch, but usually when there's a hole, the rest of the hose is in pretty bad shape.
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