Symptom: when this 1987 300D is fully warmed, at a stop light, foot on brake.... purring smoothly at idle, the engine RPM jumps (up) for a fraction of a second (maybe 1/10 second). Like somebody tapped the accelerator pedal. Happens unpredictably and only occasionally, seems to be getting a little more frequent. Currently, happens maybe once or twice per drive cycle at the most, often never. Also, it's been tossing a couple in a row, not necessarily back-to-back but within moments of each other. I thought (was hoping) it was a passing minor thing, but seems to be going in the other direction hence the post.

It's over so quickly I can't get a reading on the tach to see how much RPM is gained, but it's not huge or anything. Reminds me of a heart palpitation or a flutter that pumps a couple extra squirts and then calms down, like something is skipping ahead a couple beats. It's always an RPM gainer, never a dip. Normal idle at all other times, normal pedal to power response in all other regards. No knocks or ticks or abnormal rattles. Only seems to happen on a warm engine.

What is going on?

Some particulars I know you might be thinking of... EGR is removed and blocked off, associated pods gone and associated vac lines plugged, intake tract reasonably clean last time I looked (month ago), trapox done long ago, cat converter is gone so no exhaust pluggage. Injector nozzles (Monark) have less than a year on them, balanced when they went it and set to 2000psi. I'm guessing this new thing is IP related??

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Cheers!
Scott McPhee

1987 300D